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dennis2399
dennis2399
Associate II
September 22, 2015
Question

STM32F4 USART2 TX using DMA (with StdPeriph_Driver)

  • September 22, 2015
  • 6 replies
  • 1762 views
Posted on September 22, 2015 at 14:58

 

 

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    6 replies

    waclawek.jan
    waclawek.jan
    Super User
    September 22, 2015
    Posted on September 22, 2015 at 15:14

    Divide et impera: UART Tx alone works (perhaps in a loop, avoiding DMA in the first step)?

    JW
    keaven
    keaven
    Associate III
    September 22, 2015
    Posted on September 22, 2015 at 15:52

    It is not in your post but do you have yourUSART2_IRQHandler() ? You need it even if you are using the DMA.

    Like this 

    void USART2_IRQHandler(void)
{
HAL_UART_IRQHandler(&hUART2);
}

    This is with HAL library but you still need to manage your UART Flags in the IRQ.
    Tesla DeLorean
    Tesla DeLorean
    Guru
    September 22, 2015
    Posted on September 22, 2015 at 15:53

    I suspect there will be issues with pacing (no flow control between two streams), and there's inconsistency in data size, ie 16-bit data, vs 8-bit data.

    So you'll want to think about the disparity between the data rates, consider using HT/TC for the ADC, and then lighting off a Normal DMA transfer to the USART from the alternating halves of the ADC buffer.

    I think I've posted a couple USART TX DMA examples, including ones that cycle through multiple strings (aka buffers).

    Tips, Buy me a coffee, or three.. PayPal Venmo (See Profile) Up vote any posts that you find helpful, it shows what's working..
    waclawek.jan
    waclawek.jan
    Super User
    September 22, 2015
    Posted on September 22, 2015 at 16:24

    > It is not in your post but do you have your USART2_IRQHandler() ?  You need it even if you are using the DMA.

    Certainly not.

    > This is with HAL library but you still need to manage your UART Flags in the IRQ.

    Certainly not; contrary, you need DMA to handle them.

    JW

    keaven
    keaven
    Associate III
    September 22, 2015
    Posted on September 22, 2015 at 17:12

    You are right!  I have it for my transfer complete interrupt on TX.

    dennis2399
    dennis2399Author
    Associate II
    September 23, 2015
    Posted on September 23, 2015 at 11:53

    I appeared to be missing a line in my GPIO config for the TX pin. 

    /* Connect USART pins to AF */
GPIO_PinAFConfig(GPIOA, GPIO_PinSource2, GPIO_AF_USART2);

    After using this I got it working at the 115200 baudrate, after upping this to 2625000 I had to use the oversampling command. Using no flow control seems to work when using a terminal program but I guess it could be added for more stability. I guess I don't need any of the USART IRQ handlers since, I configured DMA1 to handle the USART Tx requests with the following line: 

    /* Enable the USART Tx DMA request */
USART_DMACmd(USART2, USART_DMAReq_Tx, ENABLE);

    Since both DMA streams are not running parallel but one after another this seems to check out. The mismatch of 16-bit ADC values being transferred over an 8-bit USART line is currently being handled on the receiving end where I perform an fread which expects uint16 values. It's not flawless yet but I'm on my way :) Thank you already for all of your responses!
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