Limiting DMX Frame Rate

2024-04-28 15:04 UTC gpt-4 Open in ChatGPT ↗

This is a DMX library for the arduino due uusing interrupts. the problem is that the DMX hardware sends values too often and it slows down my arduino. Is there a way in the begin() function of my c++ library to limit the rate i’m receiving?

// Configure PMC
pmc_enable_periph_clk(_dwId);

// Disable PDC channel
_pUsart->US_PTCR = US_PTCR_RXTDIS | US_PTCR_TXTDIS;

// Reset and disable receiver and transmitter
//_pUsart->US_CR = US_CR_RSTRX | US_CR_RSTTX | US_CR_RXDIS | US_CR_TXDIS ;
_pUsart->US_CR = US_CR_RSTRX | US_CR_RSTTX | US_CR_TXDIS;

// Configure mode
_pUsart->US_MR = US_MR_USART_MODE_NORMAL | US_MR_USCLKS_MCK | US_MR_CHRL_8_BIT | US_MR_PAR_NO |
                 US_MR_NBSTOP_2_BIT | US_MR_CHMODE_NORMAL;

// Configure baudrate, asynchronous no oversampling
_pUsart->US_BRGR = (SystemCoreClock / (250000 * 16));

// Configure interrupts
_pUsart->US_IDR = 0xFFFFFFFF;
// _pUsart->US_IER = US_IER_RXRDY | US_IER_OVRE| US_IER_FRAME | US_IER_RXBRK | US_IER_TXRDY | US_IER_TXEMPTY;

// _pUsart->US_IER = US_IER_RXRDY | US_IER_RXBRK | US_IER_TXRDY;
_pUsart->US_IER = US_IER_RXRDY | US_IER_RXBRK;

// first thing to do is generate break
//_txState = TX_BREAK;

// Set receiver state to IDLE initially
_rxState = IDLE;

// Enable receiver and transmitter
//_pUsart->US_CR = US_CR_RXEN | US_CR_TXEN;

// Enable receiver, disable transmitter
_pUsart->US_CR = US_CR_RXEN;

// Enable UART interrupt in NVIC
NVIC_EnableIRQ(_dwIrq);

To handle the issue of receiving DMX data too frequently and causing the Arduino Due to slow down, you can introduce a mechanism to effectively limit the rate at which your system processes incoming DMX frames. Here are a few approaches you could consider:

1. Software Timing Control

Implement a simple timing control to limit how often the DMX frames are processed. You can introduce a variable to store the last time a frame was processed and check against this before processing a new frame.

Here’s how you could modify the begin() function or possibly the interrupt service routine to incorporate a timing mechanism:

#include <Arduino.h>

volatile unsigned long lastFrameTime = 0;
const unsigned long frameInterval = 100; // Time in milliseconds between frame processing

void handleDMXData() {
    unsigned long currentTime = millis();
    if ((currentTime - lastFrameTime) >= frameInterval) {
        lastFrameTime = currentTime;
        // Process DMX frame
    }
}

// In your interrupt service routine or wherever you check for received data
void USART_Handler() {
    if (_pUsart->US_CSR & US_CSR_RXRDY) {  // Check if data received
        handleDMXData();
    }
}

2. Modify Interrupt Enable Settings

Another approach is to enable and disable the RXRDY interrupt based on whether you are ready to process another frame. This can be controlled by a timer or simply toggling the enable state based on processing state.

// Enable RXRDY interrupt
_pUsart->US_IER = US_IER_RXRDY;

// Disable RXRDY interrupt after processing a frame to stop processing new data
_pUsart->US_IDR = US_IER_RXRDY;

3. Using Hardware Features

The USART hardware in the Arduino Due might have features that allow for adjusting the hardware to ignore frames that are too close together, though this is typically less common in USART configurations.

4. Buffer Management

If your library and application design allow, managing how data is buffered and processed can also provide a way to control how often data is handled. You could adjust buffer thresholds and only process data when enough data has been received, or at specific intervals.

Integration in Your Code

The exact integration depends on how the rest of your library is structured, especially with respect to handling interrupts and processing data. You need to ensure that the addition of these controls doesn’t lead to missed data that is critical, or, conversely, data overflow. The best approach might involve a combination of software debouncing (as shown in the first suggestion) and careful control over interrupt enabling/disabling.

Ensure that any modifications you make are tested under conditions that your typical application will face, to avoid creating new issues with data handling and processing.

Sure! Let’s break down what each line in the begin() function of your C++ library is doing, specifically for setting up a USART (Universal Synchronous/Asynchronous Receiver/Transmitter) peripheral in the context of an Arduino Due, which uses an ARM-based microcontroller.

USART Configuration Steps

Enable Peripheral Clock:
```
pmc_enable_periph_clk(_dwId);
```
This line enables the clock to the USART peripheral using its identifier _dwId. The Peripheral DMA Controller (PDC) cannot work without the peripheral clock being enabled.
Disable PDC Channel:
```
_pUsart->US_PTCR = US_PTCR_RXTDIS | US_PTCR_TXTDIS;
```
Disables the DMA channel for both reception (RXTDIS) and transmission (TXTDIS) by setting these flags in the Transfer Control Register (US_PTCR) of the USART. This is used when you don’t want to use DMA for USART data transfers.
Reset and Disable Receiver and Transmitter:
```
_pUsart->US_CR = US_CR_RSTRX | US_CR_RSTTX | US_CR_TXDIS;
```
This command resets the receiver and transmitter to clear any pending operations or errors and disables the transmitter. The receiver is not explicitly disabled here, which might be done later or handled differently based on specific needs.
Configure USART Mode:
```
_pUsart->US_MR = US_MR_USART_MODE_NORMAL | US_MR_USCLKS_MCK | US_MR_CHRL_8_BIT | US_MR_PAR_NO |
                 US_MR_NBSTOP_2_BIT | US_MR_CHMODE_NORMAL;
```
Configures the USART mode register:
- US_MR_USART_MODE_NORMAL: Sets the USART to operate in normal mode.
- US_MR_USCLKS_MCK: Selects the main clock (MCK) as the source of the baud rate generator.
- US_MR_CHRL_8_BIT: Configures character length to 8 bits.
- US_MR_PAR_NO: No parity.
- US_MR_NBSTOP_2_BIT: Two stop bits.
- US_MR_CHMODE_NORMAL: Normal channel mode.
Configure Baud Rate:
```
_pUsart->US_BRGR = (SystemCoreClock / (250000 * 16));
```
Sets the baud rate generator register (US_BRGR) using the formula provided, where SystemCoreClock is the system operating frequency. The calculation ensures the baud rate is set to what’s needed for DMX512 communication, which is typically 250 kbps.
Configure Interrupts:
```
_pUsart->US_IDR = 0xFFFFFFFF;
```
Disables all interrupts by setting the Interrupt Disable Register (US_IDR) to all 1s.
```
_pUsart->US_IER = US_IER_RXRDY | US_IER_RXBRK;
```
Enables specific USART interrupts:
- US_IER_RXRDY: Receiver ready interrupt (data available to read).
- US_IER_RXBRK: Break received interrupt.
Enable Receiver:
```
_pUsart->US_CR = US_CR_RXEN;
```
Enables the receiver part of the USART, allowing the USART to begin receiving data.
Enable UART Interrupt in NVIC:
```
NVIC_EnableIRQ(_dwIrq);
```
Enables the USART interrupt in the Nested Vector Interrupt Controller (NVIC), allowing the processor to respond to USART-specific interrupts identified by _dwIrq.

Summary

The begin() function sets up the USART for communication by configuring hardware registers for the correct operational mode, data format, and interrupt handling, tailored for DMX data reception. This includes clock setup, disabling unused features, resetting states, and enabling necessary features. The function is pivotal for ensuring that the USART peripheral behaves as expected, handling data according to the specified configuration.

In the code snippet you provided, the disabling of the Peripheral DMA Controller (PDC) channels for both reception and transmission (US_PTCR_RXTDIS | US_PTCR_TXTDIS) serves a specific purpose. This setting affects how data is handled between the USART and the memory. Here’s why these features might be disabled in the context of your setup:

1. Direct Control Over Data Handling

No DMA Usage: Disabling the DMA channels indicates that the library or application intends to manage data transfers manually rather than using Direct Memory Access (DMA). DMA can be helpful for handling large or continuous data streams efficiently by offloading the data transfer workload from the CPU. However, using DMA also adds complexity and requires additional configuration. In some cases, especially in simpler applications or when precise control over each byte of data is needed, it might be preferable to handle each USART data event directly in software via interrupts or polling.

2. Simplicity and Resource Management

Simpler Implementation: Managing USART data transfers through polling or interrupts can simplify the implementation, as it avoids the overhead of configuring and managing DMA channels. This might be particularly appealing in applications where the data rate is manageable without DMA, reducing the overall system complexity.
Avoiding Buffer Management Issues: Using DMA requires careful management of buffers and memory, and mismanagement can lead to issues like buffer overruns or the need for synchronization mechanisms. By not using DMA, the software directly handles each received or transmitted character, which can simplify buffer management and potentially reduce errors.

3. Interrupt-based Data Processing

Immediate Processing: By handling data reception and transmission directly through interrupts (or polling), the software can immediately process or respond to each byte received. This is often crucial in time-sensitive applications where each piece of data needs to be processed or acknowledged promptly.

4. Control Over Data Flow

Flow Control: In some communication protocols, particularly where timing and immediate reaction to received data are critical, having direct control over when to accept or ignore incoming data can be important. Disabling DMA ensures that the software has the opportunity to process or filter each byte of data as it arrives, based on current conditions or state.

5. DMX512 Communication Specifics

Protocol Requirements: For protocols like DMX512, precise timing and immediate processing of data are crucial. DMX512, used primarily for lighting control, has strict timing requirements that might be more easily met with interrupt-driven or polling approaches rather than DMA.

By disabling DMA, your library or application likely aims to maintain a high level of control over data handling, ensuring that the USART communication aligns closely with the operational and timing requirements of your specific application, such as controlling theater lighting or similar DMX512-dependent environments.

Disabling all interrupts with the line _pUsart->US_IDR = 0xFFFFFFFF; is a common technique used during the initialization or configuration phase of hardware peripherals like USART in microcontroller programming. This step is especially critical when setting up communication protocols and here’s why it’s done:

1. Prevent Unwanted Interrupts During Configuration

Initialization Safety: When configuring the USART, it’s possible that previous configurations or partial data might trigger interrupts. Disabling all interrupts ensures that the microcontroller doesn’t respond to any unexpected USART events while the settings are being changed. This prevents the interrupt service routines (ISR) from being called with potentially inconsistent or incomplete settings, which could lead to errors or undefined behavior.

2. Clear Pending Interrupts

Reset Interrupt Status: Another reason for writing all ones to the Interrupt Disable Register (IDR) is to clear any pending interrupts that might have been set before beginning the configuration. Even though the IDR specifically disables interrupts and does not directly clear them, this step ensures that no residual interrupts from earlier operations remain enabled, which could interfere with the new setup.

3. Controlled Interrupt Enablement

Selective Enabling: After initially disabling all interrupts, the specific interrupts that are actually needed for the application are then explicitly enabled. This selective enablement helps in managing only relevant events and reduces the processing overhead involved in handling unnecessary interrupts. In your code snippet, after all interrupts are disabled, only the US_IER_RXRDY (Receiver Ready) and US_IER_RXBRK (Break Received) interrupts are enabled:
```
_pUsart->US_IER = US_IER_RXRDY | US_IER_RXBRK;
```
This ensures that the USART will only interrupt the CPU for these specific and crucial events, aligning with the operational needs of your application, possibly focusing on handling new data arrival or specific break conditions in the DMX data stream.

4. Synchronization

Consistent State: Disabling interrupts during setup also ensures that the USART and its associated buffers or states can be synchronized without the risk of concurrent modifications from an ISR. It helps in establishing a consistent, predictable starting state once the USART is fully configured and ready to be re-enabled.

Conclusion

Thus, this method of disabling all interrupts initially and then re-enabling only the necessary ones is a standard practice to ensure a safe, controlled, and predictable USART configuration process in embedded systems. This approach minimizes the risk of glitches, race conditions, and other errors that might occur if interrupts were allowed during peripheral reconfiguration.

The setup code you’ve shared primarily configures the USART (Universal Synchronous Asynchronous Receiver Transmitter) for communication, specifically aimed at handling DMX512, a protocol often used in lighting technology. Let’s analyze whether there’s anything in the configuration that directly impacts the frame rate or could introduce delays in the handling of data:

USART Baud Rate Configuration

_pUsart->US_BRGR = (SystemCoreClock / (250000 * 16));

This line sets the baud rate for the USART communication. The baud rate is calculated based on the SystemCoreClock, which is the clock frequency of the microcontroller, and is set to 250,000 bits per second (bps), which is typical for DMX512 communication. The baud rate itself directly influences how fast data is transmitted and received but does not inherently define the frame rate of the DMX protocol, which is usually around 44 frames per second. This setting shouldn’t introduce delays unless the SystemCoreClock is not configured correctly or there are clock stability issues.

Interrupt Configuration

_pUsart->US_IDR = 0xFFFFFFFF;
_pUsart->US_IER = US_IER_RXRDY | US_IER_RXBRK;

Here, all interrupts are initially disabled, and then interrupts for receiver ready (RXRDY) and break received (RXBRK) are enabled. This setup means the microcontroller will only respond to these two events:

RXRDY (Receiver Ready): An interrupt is generated whenever there is data available to be read from the USART. This should facilitate quick data handling as it allows the processor to react immediately when data arrives.
RXBRK (Break Received): An interrupt for detecting a break condition on the USART line, which is critical for DMX512 since a break signals the start of a new DMX frame.

Neither of these settings should introduce inherent delays in frame handling; in fact, they are configured to ensure timely processing of each frame and the start of new frames.

Receiver and Transmitter Settings

_pUsart->US_CR = US_CR_RXEN;

This line enables the receiver but does not enable the transmitter. This setting is focused on receiving data and does not impact the processing of incoming data frames in terms of adding delay. It ensures that the device is ready to receive data as soon as it starts coming in without waiting for transmitter readiness.

Potential Sources of Delays

Processor Overhead: If the microcontroller is performing other tasks or if the ISR for handling USART data is not efficiently implemented, this could introduce processing delays.
Software Timing Control: If there are additional layers of software managing when and how data is processed (like checking buffer states or additional error handling in the ISR), these could theoretically introduce delays.
Hardware Limitations: The capability of the microcontroller to handle high rates of incoming data without buffer overflow or other resource contention issues might also impact responsiveness.

Conclusion

The settings in your provided begin() function are optimized for receiving DMX512 data without inherent delays from configuration. Any delays would more likely stem from external factors such as overall system load, the efficiency of your interrupt service routines, or physical layer issues (like signal integrity problems). If you’re experiencing delays, it might be worth investigating these areas or looking at how data is processed after it’s received to identify potential bottlenecks.

USART Interrupts Overview

For the USART (Universal Synchronous/Asynchronous Receiver/Transmitter) used in the Arduino Due, which is based on the Atmel SAM3X8E ARM Cortex-M3 processor, there are several interrupt types that can be enabled or disabled. These include:

RXRDY (Receiver Ready): Interrupt is triggered when there is new data available in the USART receiver holding register, indicating that data can be read.
TXRDY (Transmitter Ready): Interrupt is triggered when the transmitter is ready to accept new data; useful for non-blocking data transmission.
RXBRK (Break Received): Indicates that the break condition was detected on the USART input.
ENDRX (End of Receiver Transfer): Indicates the end of a receiver transfer if using the DMA controller.
ENDTX (End of Transmitter Transfer): Indicates the end of a transmitter transfer if using the DMA controller.
OVRE (Overrun Error): Triggered when an overrun error occurs; the receive buffer was not read before the next frame was received.
FRAME (Framing Error): Occurs when a framing error is detected.
PARE (Parity Error): Occurs when a parity error is detected in the received data.
TIMEOUT (Receiver Time-out): Triggered when the receiver has not received any data within a programmable time-out period.
TXEMPTY (Transmitter Empty): Triggered when the transmitter has completely emptied all data in the buffer.
ITER (Max Iterations): Indicates that the maximum number of iterations has been reached for multi-drop communication.
NACK (Non-Acknowledge Interrupt): Occurs if a non-acknowledge signal is detected.
RIIC (Ring Indicator Input Change): Indicates a change in the level of the ring indicator signal.
DSRIC (Data Set Ready Input Change): Indicates a change in the level of the data set ready signal.
DCDIC (Data Carrier Detect Input Change): Indicates a change in the level of the data carrier detect signal.
CTSIC (Clear to Send Input Change): Indicates a change in the level of the clear to send signal.
MANE (Manchester Error): Occurs if a Manchester encoding error is detected.

Interference from Other Libraries

In a complex embedded system like one built around an Arduino Due, it is entirely possible for one library to interfere with another if they use the same resources, such as interrupts. Here are some considerations:

Shared Interrupt Lines: If another library uses the same USART or another peripheral with overlapping interrupt lines, and both are configured to handle interrupts, they might interfere with each other. This can happen if the interrupt handling routines are not designed to coexist, leading to conflicts or unexpected behavior.
Priority Conflicts: The NVIC (Nested Vector Interrupt Controller) in ARM processors allows for priority levels to be set for interrupts. If two interrupts have the same priority and are triggered around the same time, the processor must handle them in a predefined order, which can lead to delays or missed interrupts.
Resource Locking: If multiple libraries attempt to use the same USART, they might misconfigure the hardware or respond to interrupts that were intended for another purpose, leading to data corruption or loss.

Solutions

Exclusive Access: Ensure that no two libraries are configured to use the same USART hardware unless absolutely necessary and properly managed.
Check Library Documentation: Verify in the documentation of all used libraries whether they configure or use the same USART or interrupts.
Modify Library Code: If needed, modify one or more libraries to change the USART channel or interrupt settings to avoid conflicts.
Use Mutexes or Flags: Implement software locks or flags to manage access to shared resources among different pieces of code.
Configure NVIC Priorities: Appropriately set interrupt priorities in the NVIC to manage the handling of interrupts from different sources more effectively.

Ensuring that each part of your system is aware of others and managing shared resources appropriately is crucial for stability and performance in embedded systems.

When i disable all interrupts, all lag is gone.

check the entire code and find out why these interrupts make the motor control slow

//#include <string.h> //#include <arduino.h> #include “DmxDue.h”

// Constructors DmxDue::DmxDue(Usart *pUsart, IRQn_Type dwIrq, uint32_t dwId, uint8_t *pRx_buffer, uint8_t *pTx_buffer) { _rx_buffer = pRx_buffer; _pUsart = pUsart; _dwIrq = dwIrq; _dwId = dwId;

_tx_buffer = pTx_buffer;
_txReadyEvent = NULL;
_rxReadyEvent = NULL;

_rxCnt = 0;
_rxLength = 0;

clrTxBuffer();
setTxMaxChannels(DMX_TX_MAX);

_rxState = RX_OFF;
_txState = TX_OFF;

}

/* --------- transmitter ---------- */

// clear transmit buffer void DmxDue::clrTxBuffer() { for (uint16_t i = 0; i < DMX_TX_MAX; i++) { _tx_buffer[i] = 0; } }

// set max transmit channels void DmxDue::setTxMaxChannels(uint16_t maxChannels) { if (maxChannels > DMX_TX_MAX) _maxTxChannels = DMX_TX_MAX; else _maxTxChannels = maxChannels; }

// write value to transmit buffer void DmxDue::write(uint16_t channel, uint8_t value) { // sanity check if (channel == 0 || channel > DMX_TX_MAX) return;

_tx_buffer[channel - 1] = value;

}

// get value from transmit buffer uint8_t DmxDue::getTx(uint16_t channel) { // sanity check if (channel == 0 || channel > DMX_TX_MAX) return 0;

return _tx_buffer[channel - 1];

} /* --------- receiver ---------- */

// return dmx value from channel uint8_t DmxDue::read(uint16_t channel) { // sanity check if (channel == 0 || channel > DMX_RX_MAX) return 0;

return _rx_buffer[channel];

}

uint16_t DmxDue::getRxLength() { return _rxLength; }

// initialise hardware void DmxDue::begin() { // Configure PMC pmc_enable_periph_clk(_dwId);

// Disable PDC channel
_pUsart->US_PTCR = US_PTCR_RXTDIS | US_PTCR_TXTDIS;

// Reset and disable receiver and transmitter
//_pUsart->US_CR = US_CR_RSTRX | US_CR_RSTTX | US_CR_RXDIS | US_CR_TXDIS ;
_pUsart->US_CR = US_CR_RSTRX | US_CR_RSTTX | US_CR_TXDIS;

// Configure mode
_pUsart->US_MR = US_MR_USART_MODE_NORMAL | US_MR_USCLKS_MCK | US_MR_CHRL_8_BIT | US_MR_PAR_NO |
                 US_MR_NBSTOP_2_BIT | US_MR_CHMODE_NORMAL;

// Configure baudrate, asynchronous no oversampling
_pUsart->US_BRGR = (SystemCoreClock / (250000 * 16));

// Configure interrupts
_pUsart->US_IDR = 0xFFFFFFFF;
// _pUsart->US_IER = US_IER_RXRDY | US_IER_OVRE| US_IER_FRAME | US_IER_RXBRK | US_IER_TXRDY | US_IER_TXEMPTY;

// _pUsart->US_IER = US_IER_RXRDY | US_IER_RXBRK | US_IER_TXRDY;
 _pUsart->US_IER = US_IER_RXRDY | US_IER_RXBRK;

// first thing to do is generate break
_txState = TX_BREAK;

// Set receiver state to IDLE initially
_rxState = IDLE;

// Enable receiver and transmitter
//_pUsart->US_CR = US_CR_RXEN | US_CR_TXEN;

// Enable receiver, disable transmitter
_pUsart->US_CR = US_CR_RXEN;

// Enable UART interrupt in NVIC
NVIC_EnableIRQ(_dwIrq);

}

void DmxDue::setRxEvent(Fptr f) { _rxReadyEvent = f; }

void DmxDue::setBreakEvent(Fptr f) { _txReadyEvent = f; }

void DmxDue::markAfterBreak() { // stop brake _pUsart->US_CR |= US_CR_STPBRK; }

// Send start code void DmxDue::beginWrite() { _pUsart->US_THR = 0; _txCnt = 0; _txState = TX_DATA; // next state }

void DmxDue::setInterruptPriority(uint32_t priority) { NVIC_SetPriority(_dwIrq, priority & 0x0F); }

// all usartX interupts together void DmxDue::IrqHandler(void) {

if (_rxState == RX_OFF && _txState == TX_OFF) return;

uint32_t status = _pUsart->US_CSR;   // get state before data!

// Did we receive data ?
if (status & US_CSR_RXRDY) {
    uint8_t dmxByte = _pUsart->US_RHR;    // get data

    switch (_rxState) {
        case BREAK:
            // first byte is the start code
            _rx_buffer[0] = dmxByte;
            if (dmxByte == 0) {
                _rxState = DATA;  // normal DMX start code detected
                _rxCnt = 1;       // start with channel # 1
            } else { ;//_rxState = IDLE; //  wait for next BREAK !
            }
            break;
        case DATA:
            _rx_buffer[_rxCnt] = dmxByte;    // store received data into dmx data buffer
            if (_rxCnt < DMX_RX_MAX) {
                _rxCnt++; // next channel
            } else {
                _rxState = IDLE;    // wait for next break
            }
            break;
        case IDLE:
        default:
            break;
    }
}

// Receiver Break = frame error
if (status & US_CSR_RXBRK) {    //check for break
    _rxState = BREAK; // break condition detected.
    if (_rxCnt > 1) _rxLength = _rxCnt - 2; // store dmx length
    else _rxLength = 0;
    _pUsart->US_CR |= US_CR_RSTSTA;
    if (_rxReadyEvent && _rxLength) _rxReadyEvent();
}

// tx ready
if (status & US_CSR_TXRDY) {

    switch (_txState) {
        case TX_DATA:
            // Send character
            _pUsart->US_THR = _tx_buffer[_txCnt];
            if (_txCnt < _maxTxChannels - 1) {
                _txCnt++;
            } else {
                _txState = TX_BREAK;// next state
            }
            break;
        case TX_BREAK:
            // send first break byte
            _pUsart->US_CR |= US_CR_STTBRK;
            _pUsart->US_THR = 0;
            _txState = TX_BREAK1;
            break;

        case TX_BREAK1:
            // send 2-nd break byte
            _pUsart->US_THR = 0;
            _txState = TX_BREAK2;
            break;

        case TX_BREAK2:
            // send 3-th break byte
            _pUsart->US_THR = 0;
            // break must be at leat 88 uSec so , 44 uSec to go
            if (_txReadyEvent) _txReadyEvent();
            _txState = TX_START;
            break;
        case TX_START:

            _pUsart->US_CR |= US_CR_STPBRK; //Stop Break. 2 stop bits from break bytes will working as Mark After Break

            _pUsart->US_THR = 0; // Send INIT
            _txCnt = 0;
            _txState = TX_DATA;  // next state

        case TX_DISABLE:
        default:
            // Mask off transmit interrupt so we don't get it anymore
            //_pUsart->USART_IDR = USART_IDR_TXRDY;

            break;

    }

}

/*
// Acknowledge errors
if (status & US_CSR_OVRE)
{
  // TODO: error reporting outside ISR
  _pUsart->US_CR |= US_CR_RSTSTA;
}
*/

}

// ---------------------------------------------------------------------------- /*

USART objects */

// Array of DMX values (raw). // Entry 0 will never be used for DMX data but will store the startbyte (0 for DMX mode).

#ifdef DMX1 uint8_t dmx_rx_buffer1[DMX_RX_MAX + 1]; uint8_t dmx_tx_buffer1[DMX_TX_MAX]; // Create class instances DmxDue DmxDue1(USART0, USART0_IRQn, ID_USART0, dmx_rx_buffer1, dmx_tx_buffer1);

// IT handlers void USART0_Handler(void) { DmxDue1.IrqHandler(); }

#endif #ifdef DMX2 uint8_t dmx_rx_buffer2[DMX_RX_MAX + 1]; uint8_t dmx_tx_buffer2[DMX_TX_MAX]; DmxDue DmxDue2(USART1, USART1_IRQn, ID_USART1, dmx_rx_buffer2, dmx_tx_buffer2);

void USART1_Handler( void ) { DmxDue2.IrqHandler() ; } #endif #ifdef DMX3 uint8_t dmx_rx_buffer3[DMX_RX_MAX + 1]; uint8_t dmx_tx_buffer3[DMX_TX_MAX]; DmxDue DmxDue3(USART3, USART3_IRQn, ID_USART3, dmx_rx_buffer3, dmx_tx_buffer3);

void USART3_Handler( void ) { DmxDue3.IrqHandler() ; } #endif

#ifdef DMX4 //Spare unlisted USART on the board uint8_t dmx_rx_buffer4[DMX_RX_MAX + 1]; uint8_t dmx_tx_buffer4[DMX_TX_MAX]; DmxDue DmxDue4(USART2, USART2_IRQn, ID_USART2, dmx_rx_buffer4, dmx_tx_buffer4);

void USART2_Handler( void ) { DmxDue4.IrqHandler() ; } #endif

Given that disabling all interrupts eliminates lag in motor control, this suggests that the interrupt service routines (ISRs) are consuming significant processor resources, potentially interfering with the timely execution of other critical tasks, such as motor control. Here’s a breakdown of possible causes for the slowdown based on the code you’ve provided:

1. Complex and Frequent ISR Execution

The IrqHandler() function handles multiple conditions and states, processing both receive (RX) and transmit (TX) data. This ISR might be invoked very frequently due to the nature of DMX communication, which requires handling hundreds of packets per second. Each packet can generate an interrupt when received or ready to send:

Receiving Data: The ISR handles different states like BREAK, DATA, and IDLE. If the DMX signal is continuous and each state transition generates an interrupt, the CPU spends a considerable amount of time managing state transitions and data buffering within the ISR.
Transmitting Data: The ISR also handles the transmission of data, including sending breaks and actual DMX data. The state machine for managing transmission states (TX_DATA, TX_BREAK, TX_BREAK1, etc.) involves multiple steps and potential ISR re-entry points which can be particularly CPU-intensive.

2. Interrupt Handling Overhead

The USART hardware triggers interrupts for various reasons like data ready to read (RXRDY), transmit buffer empty (TXRDY), and break signals (RXBRK). Each of these events requires immediate CPU attention. When these interrupts occur frequently:

Context Switching: The processor must save its current state and switch to the interrupt context, which adds overhead.
Interrupt Service Overhead: Handling interrupts frequently can significantly delay the execution of the main program or other lower priority tasks, such as those managing motor control.

3. Potential Priority Issues

If the USART interrupts have a higher priority than other critical tasks (like motor control), the microcontroller might delay or interrupt these tasks frequently. This can result in noticeable lag in response times for motor control operations.

4. Resource Contention

If motor control also relies on interrupts or shares certain resources with the DMX handling (like timers or other I/O interfaces), the heavy usage of CPU time by USART interrupts can starve these other components of necessary CPU cycles.

Solutions:

To mitigate the impact of USART interrupts on motor control performance, consider the following strategies:

Optimize ISR Code: Ensure that the ISR is as lightweight as possible. For instance, minimize the processing done within the ISR and avoid complex logic or function calls that can be handled outside the ISR.
Interrupt Throttling: Implement a mechanism to limit the rate at which interrupts are serviced. This could involve selectively enabling/disabling interrupts based on system load or other runtime conditions.
Priority Adjustment: Check and adjust the priority levels of the interrupts. Make sure that the motor control tasks have appropriate priority relative to the USART tasks to prevent motor tasks from being delayed excessively.
Buffer Management: Increase buffer sizes or manage buffers more efficiently to reduce the frequency of interrupts due to buffer overflows or underflows.
Task Scheduling: If possible, re-evaluate the scheduling of tasks within your application. Ensure that time-critical tasks (like motor control) are handled appropriately with real-time considerations.

By applying these strategies, you can better balance the handling of DMX data with other critical system tasks, thereby enhancing overall system responsiveness and performance.

Adjusting interrupt priorities on an ARM Cortex-M3 processor, like the one in the Arduino Due, involves interacting with the Nested Vector Interrupt Controller (NVIC). This controller manages priorities among various interrupts, allowing you to configure which interrupts can preempt others and how the processor should handle multiple interrupt requests.

Step-by-Step Guide to Adjusting Interrupt Priority

Here’s how you can adjust the interrupt priorities in your code:

Understand Priority Levels:
- The ARM Cortex-M3 processor uses a priority level scheme where a lower number indicates a higher priority. The range of priority levels can vary but typically ranges from 0 (highest priority) to a maximum that depends on the implementation (commonly 15 or 255).
Locate NVIC Priority Function: In the Arduino environment and in many ARM Cortex-M3 implementations, the function NVIC_SetPriority() is used to set the priority of an interrupt. You’ve already seen this in your existing code snippet.
Set Priority: You need to decide on the priorities based on your application needs. For example, if motor control is critical, you might want to set its interrupt priority higher (i.e., a lower number) than other less critical tasks.

Here’s how you can set the priority:
```
NVIC_SetPriority(IRQn_Type IRQn, uint32_t priority);
```
- IRQn: This is the identifier of the interrupt for which the priority is being set.
- priority: This is the priority level for the interrupt. Remember that a lower value means a higher priority.
Example Code: Assuming you have an interrupt handler for motor control and its IRQn is defined (let’s assume MotorControl_IRQn), and you want to set it to a higher priority than the USART interrupts, you might write:
```
NVIC_SetPriority(MotorControl_IRQn, 2);  // Set motor control interrupt to higher priority
NVIC_SetPriority(USART0_IRQn, 5);        // Set USART0 interrupt to a lower priority
```
Adjust these values according to your system’s requirements. If motor control isn’t specifically interrupt-driven but needs to be highly responsive, consider adjusting the priorities of the interrupts that could affect its performance (like your USART interrupts).
Implement Changes and Test: After adjusting priorities, thoroughly test your system to ensure that the changes have the desired effect on responsiveness and that no new issues are introduced.
Consider Preemption Thresholds: Cortex-M3 also supports setting a preemption threshold, which allows certain interrupts to be non-preemptive if their priority is below a certain threshold. This feature can be configured via system control registers but is usually not necessary for simpler applications like those typically run on Arduino platforms.

Good Practices

Balance Priority Settings: While it might be tempting to give all critical tasks the highest priority, this can lead to lower priority tasks being starved of CPU time, potentially causing system instability or missed events.
Test Under Load: Simulate the highest expected load on your system and verify that the interrupt priorities you’ve set allow the system to operate correctly.
Document Changes: Keep a record of priority settings and the rationale for these settings, as part of your system documentation, which can help in future troubleshooting and maintenance.

Adjusting interrupt priorities is a powerful tool in real-time systems programming that allows you to tailor the responsiveness of your system to meet specific operational requirements.

To modify the behavior of your system so that it only services interrupts every 100 milliseconds, you can introduce a timing control mechanism directly into your interrupt service routine (ISR). This approach will use a simple timer or timestamp check to determine if enough time has elapsed since the last processing of an interrupt.

Step 1: Add a Timing Mechanism

First, you will need to define a global variable to keep track of the last time the ISR was executed. This variable should be declared as volatile because it is updated in an ISR and read in the main program (or potentially other ISRs).

Step 2: Update the `IrqHandler` Function

In the IrqHandler function, add a check to see if 100ms have passed since the last time the interrupts were handled. If less than 100ms has passed, the function will return immediately without processing anything.

Here is how you can integrate this into your existing code:

#include <Arduino.h>

// Global variable to track the last time ISR was executed
volatile unsigned long lastInterruptTime = 0;
const unsigned long interruptInterval = 100;  // Interrupt service interval in milliseconds

void DmxDue::IrqHandler(void) {
    unsigned long currentTime = millis();
    // Check if 100ms have passed since last interrupt handling
    if ((currentTime - lastInterruptTime) < interruptInterval) {
        return;  // Not enough time has passed, exit the ISR
    }
    lastInterruptTime = currentTime;  // Update the last interrupt time

    uint32_t status = _pUsart->US_CSR;  // get state before data!

    // The rest of your existing ISR code follows...
    // For example:
    if (status & US_CSR_RXRDY) {
        uint8_t dmxByte = _pUsart->US_RHR;    // get data
        // Handle the RX data
        // [...]
    }

    if (status & US_CSR_RXBRK) {
        // Handle break detection
        // [...]
    }

    // Handle other cases like TX ready, etc.
    // [...]
}

Explanation

Timing Control: The millis() function returns the number of milliseconds since the Arduino board began running the current program. This duration is used to ensure that the ISR code executes only after at least 100 milliseconds have passed since it was last executed.
Efficiency: This method efficiently throttles the ISR execution rate without affecting the timer or delay functionalities of other system components.
Global Variables: The use of volatile ensures that the variable lastInterruptTime is accessed correctly in the context of multiple execution threads (like normal execution flow and ISRs).

Testing and Validation

After implementing this change:

Test under various conditions to ensure that no events are missed and that the system behaves as expected under all operating conditions.
Monitor system performance to confirm that this modification effectively balances responsiveness with processing needs.
Adjust the interruptInterval as necessary depending on the real-time requirements and performance observations.

This approach should help manage the responsiveness of your system by limiting how often the interrupts are handled, potentially reducing the impact on other critical tasks such as motor control.

The modification to handle interrupts every 100 milliseconds could potentially cause issues with DMX data reception, especially since DMX512 is a time-sensitive protocol. If interrupts are not handled frequently enough, you might miss critical data frames or break signals that are essential for DMX communication.

Understanding the Problem:

DMX512 has a baud rate of 250 kbps, which equates to about 44 microseconds per bit. A full DMX frame, including the start bit, 8 data bits, and 2 stop bits, takes about 4.4 milliseconds to transmit. If your interrupt handler is only running every 100 milliseconds, you would only process approximately every 22nd frame or so, leading to data loss and incomplete DMX messages.

Possible Solutions:

To ensure proper DMX data handling while still managing system performance, consider the following alternatives:

1. Buffer Incoming Data:

Modify your USART configuration to use a larger hardware buffer if available. This way, even if the ISR is not servicing the buffer quickly, the USART hardware might be able to store more incoming data until it can be processed.

Example (for USARTs with buffering capabilities):

// Configure the USART buffer size (if supported)
_pUsart->US_RTOR = USART_TIMEOUT;  // Set receiver timeout
_pUsart->US_FMR = USART_FIFO_MODE; // Enable FIFO mode if available

2. Optimize ISR Execution Time:

Instead of limiting ISR execution frequency, focus on making the ISR itself more efficient. Ensure that it only does minimal work – reading from or writing to buffers, setting flags, etc., and deferring any processing out of ISR.

Refined ISR Example:

void DmxDue::IrqHandler(void) {
    uint32_t status = _pUsart->US_CSR;  // Get the status before data

    if (status & US_CSR_RXRDY) {
        uint8_t dmxByte = _pUsart->US_RHR;    // Get data
        // Quickly store data in buffer and exit
        buffer.enqueue(dmxByte);  // Assuming buffer is a queue that can store bytes
    }

    if (status & US_CSR_RXBRK) {
        // Handle break detection quickly
        handleBreakDetection();
    }

    // Additional cases
}

3. Adjust System Design:

If the DMX library and motor control functions are both critical and their performance is conflicting, consider using a separate microcontroller or processor for each task, or prioritize the interrupts effectively based on real-time performance requirements.

4. Use Direct Memory Access (DMA):

If your hardware supports DMA, configure the USART to use DMA for receiving data. This will offload the work of data transfer from the CPU, allowing the USART to receive data and store it in memory without CPU intervention, thus freeing up CPU cycles.

Configuring DMA (Pseudo Code):

// Enable DMA controller
enable_DMA_controller();
// Set up DMA transfer for USART RX
setup_DMA_for_USART_RX(_pUsart, DMA_Channel, buffer);

Testing:

After implementing any of these changes, perform comprehensive testing under realistic load scenarios to ensure that both DMX reception and motor control operate reliably and without interfering with each other. Monitor the system to verify that the timing of DMX frames and motor control signals are within acceptable limits for your application.

To modify the begin() function to use DMA (Direct Memory Access) for handling USART communication in an Arduino Due (which is based on the Atmel SAM3X8E ARM Cortex-M3 processor), you will need to set up both the USART peripheral and the DMA controller properly. This involves configuring the USART to work with the DMA for receiving (and optionally transmitting) data, and setting up the DMA controller to handle data transfers directly between the USART data registers and memory buffers without CPU intervention.

Here’s a step-by-step guide on how to modify the begin() function to integrate DMA:

1. Include DMA Library and Define Buffers

First, ensure you have appropriate DMA library support and define buffers that the DMA will use for USART data transfers.

#include <dma.h>  // Make sure you have a DMA library or DMA functions available

uint8_t rxBuffer[DMX_RX_MAX];  // Define RX buffer for DMA to store received data

2. Initialize DMA

Before configuring USART, initialize and configure the DMA controller and channels.

void setupDMAForUSART(Usart* usart) {
    // Assuming a function that setups DMA; implement according to your DMA controller specifics
    dma_init();
    dma_configure_channel(USART_DMA_CHANNEL_RX,
        (uint32_t)&usart->US_RHR,  // Source: USART Receive Holding Register
        (uint32_t)rxBuffer,        // Destination: RX buffer
        DMX_RX_MAX);               // Length of DMA transfer
}

3. Modify `begin()` Function

Incorporate DMA setup into the begin() function, ensuring that USART is set to work with the DMA controller.

If the callback function in your Arduino code is still being called even when the ENTTEC DMXUSB Pro hardware is unplugged, there are a few possible reasons why this might be happening. Understanding each will help determine the best course of action to resolve the issue:

1. Noise and Hardware Disconnections

Noise: When DMX hardware like the ENTTEC DMXUSB Pro is disconnected, the DMX lines might pick up electrical noise. Since DMX is a differential signal, normally it’s robust against such noise, but when disconnected, this can lead to erroneous signals that the receiver (your Arduino) might interpret as valid DMX data.
Hardware Condition: Check the condition of your cables, connectors, and the physical DMX ports. Sometimes, faulty hardware can generate unexpected behavior.

2. Software Misinterpretation

Buffer Residuals: If there’s any residual data left in buffers, it might cause the software to think new data has arrived and thereby trigger callbacks.
State Machine Errors: If your software uses a state machine to manage DMX data processing, ensure that state transitions correctly handle the disconnection scenario. An incorrect state might misinterpret noise or buffer residuals as valid data.

3. Interrupt Misfires

Floating Inputs: If the DMX input pin on the Arduino is left floating (not pulled to a defined voltage level when disconnected), it might randomly switch between high and low states due to electromagnetic interference from the environment. This can erroneously trigger the interrupts.
Debounce Logic: Consider implementing a debounce logic or a confirmation mechanism that validates the DMX signal for a certain duration or number of frames before processing.

4. Firmware Bugs

Check Firmware: Review the logic that determines when the callback function is called. Look for any conditions that might incorrectly assess when to call the function. Ensure that all pathways that lead to the callback being called are appropriate and consider adding additional checks to confirm the presence of a valid DMX signal.

Testing and Debugging Steps

Signal Monitoring: Use an oscilloscope or a logic analyzer to monitor the DMX input pin when the hardware is disconnected. Check if there are any unwanted signals or noise.
Software Debugging: Add serial print statements or other debugging outputs in your callback function and related areas to track the flow of execution and state changes.
Improve Input Handling:
- Add a pull-down resistor to the DMX input pin to ensure it doesn’t float when disconnected.
- Implement a software filter or a timeout mechanism that detects sustained signal loss and prevents the callback from being triggered.
Validate DMX Start Code: Ensure your software checks for a valid DMX start code before processing any received data. Typically, the start code for standard DMX data is 0x00.

Code Snippet Example for Improved Handling

Here’s a simple example of how you might modify your interrupt service routine or data handling logic to include some basic noise filtering:

void handleDMXDataInterrupt() {
    if (!isDMXConnected()) {
        return;  // Avoid processing when DMX is disconnected
    }

    // Read data and process
    uint8_t dmxData = readDMXData();
    if (dmxDataIsValid(dmxData)) {
        triggerCallback();
    }
}

bool isDMXConnected() {
    // Implement logic to check if the DMX device is connected or not
    // This might be a simple timeout check to see when the last valid DMX frame was received
    return millis() - lastValidDMXFrameTime < DMX_TIMEOUT;
}

bool dmxDataIsValid(uint8_t data) {
    // Additional validation logic for DMX data
    return data == EXPECTED_START_CODE;  // Simple start code check
}

Adjust and expand upon these concepts based on the specific behavior observed and the results of your testing.