STM32 DMA badly need working example

[mati294]

Hello, I need a good example for STM32 DMA with data reception and transmission.
I tried something with chatgpt and it partially works, but it's terribly unstable, or the DMA buffer gets ripped apart when the frame starts reading via Modbus so I need help.

[mati294]

Tested for a Slave/Server with RS485 hardware vlow control.

So I made it work (probably fairly correctly) with the computer as the master QMaster.
Modbuspool works in HAL_UARTEx_RxEventCallback with synchronization, or in main(), if you prefer.
DMA Buffer as normal (I couldn't get it to work stably with circular). Tested below 100ms and its work but QMaster is not great for that...
Code is parialy generated by chatgpt and probably reset DMA on error is not necresary.

`
#define RX_BUF_SIZE 64
#define FRAME_MAX_SIZE 64
#define FRAME_QUEUE_LEN 4

uint8_t dma_rx_buf[RX_BUF_SIZE];

/* kolejka ramek */
typedef struct {
uint8_t data[FRAME_MAX_SIZE];
uint16_t len;
uint16_t pos;
} frame_t;

volatile frame_t frame_queue[FRAME_QUEUE_LEN];
volatile uint8_t frame_wr = 0;
volatile uint8_t frame_rd = 0;

nmbs_t nmbs;
nmbs_error err;

uint32_t errormodbus=0;

void HAL_UARTEx_RxEventCallback(UART_HandleTypeDef *huart, uint16_t size)
{
if (huart->Instance != USART1) return;
if (size == 0) goto restart;

uint8_t next = (frame_wr + 1) % FRAME_QUEUE_LEN;
if (next != frame_rd) {
    memcpy((void*)frame_queue[frame_wr].data, dma_rx_buf, size);
    frame_queue[frame_wr].len = size;
    frame_queue[frame_wr].pos = 0;
    frame_wr = next;
}
LedRGB_setRGB(&Led1, 125, 125, 0);
readData();
err = nmbs_server_poll(&nmbs);
 ModbusSync();

restart:
HAL_UARTEx_ReceiveToIdle_DMA(
huart,
dma_rx_buf,
RX_BUF_SIZE
);
__HAL_DMA_DISABLE_IT(huart->hdmarx, DMA_IT_HT);
}
void HAL_UART_ErrorCallback(UART_HandleTypeDef *huart)
{
if (huart->Instance != USART1) return;

__HAL_UART_CLEAR_OREFLAG(huart);
__HAL_UART_CLEAR_FEFLAG(huart);
__HAL_UART_CLEAR_NEFLAG(huart);
LedRGB_setRGB(&Led1, 10, 125, 125);
HAL_UARTEx_ReceiveToIdle_DMA(huart,dma_rx_buf,RX_BUF_SIZE);

HAL_UART_DMAStop(&huart1);

__HAL_UART_CLEAR_IDLEFLAG(&huart1);
__HAL_UART_CLEAR_OREFLAG(&huart1);
__HAL_UART_CLEAR_FEFLAG(&huart1);
__HAL_UART_CLEAR_NEFLAG(&huart1);
__HAL_UART_CLEAR_PEFLAG(&huart1);

memset(dma_rx_buf, 0, RX_BUF_SIZE);

for (uint8_t i = 0; i < FRAME_QUEUE_LEN; i++) {
    frame_queue[i].len = 0;
    memset((void*)frame_queue[i].data, 0, FRAME_MAX_SIZE);
}
frame_wr = 0;
frame_rd = 0;

HAL_UARTEx_ReceiveToIdle_DMA(&huart1, dma_rx_buf, RX_BUF_SIZE);
__HAL_DMA_DISABLE_IT(huart1.hdmarx, DMA_IT_HT); // half-transfer OFF

}

int32_t read_serial(uint8_t* buf, uint16_t count, //działa
int32_t timeout_ms, void* arg)
{
if (frame_rd == frame_wr)
return 0;

frame_t* f = (frame_t*)&frame_queue[frame_rd];

uint16_t remaining = f->len - f->pos;
if (remaining == 0) {
    // ramka w całości oddana → przejdź do następnej
    f->pos = 0;
    frame_rd = (frame_rd + 1) % FRAME_QUEUE_LEN;
    return 0;
}

uint16_t n = (count < remaining) ? count : remaining;
memcpy(buf, &f->data[f->pos], n);
f->pos += n;
LedRGB_setRGB(&Led1, 0, 0, 125);

return n;

}

int32_t write_serial(const uint8_t *buf, uint16_t count,
int32_t byte_timeout_ms, void arg) {
LedRGB_setRGB(&Led1, 180, 125, 0);
HAL_UART_Transmit_DMA(&huart1, (uint8_t) buf, count);
LedRGB_setRGB(&Led1, 10, 155, 0);
return count;
}
`