Re: [lwip-users] PPPoS: ppp session disconnect if hit bad fcs for LCP packet

[Sylvain Rochet]

Hi Axel,

On Sun, Jul 16, 2017 at 02:51:01PM +0800, Axel Lin wrote:
> 
> I'm running on a STM32F4 platform.
> 
> The driver uses  below settings:
> 
>     /* Fill init structure with common DMA settings */
>     dma_init_structure.DMA_PeripheralInc   = DMA_PeripheralInc_Disable;
>     dma_init_structure.DMA_MemoryInc       = DMA_MemoryInc_Enable;
>     dma_init_structure.DMA_Priority        = DMA_Priority_VeryHigh;
>     dma_init_structure.DMA_FIFOMode        = DMA_FIFOMode_Disable;
>     dma_init_structure.DMA_FIFOThreshold   = DMA_FIFOThreshold_Full;
>     dma_init_structure.DMA_MemoryBurst     = DMA_MemoryBurst_Single;
>     dma_init_structure.DMA_PeripheralBurst = DMA_PeripheralBurst_Single;
> 
>     /* Initialise RX DMA */
>     DMA_DeInit( peripheral->rx_dma_config.stream );
>     dma_init_structure.DMA_Channel            =
> peripheral->rx_dma_config.channel;
>     dma_init_structure.DMA_PeripheralBaseAddr = (uint32_t)
> &peripheral->port->DR;
>     dma_init_structure.DMA_Memory0BaseAddr    = 0;
>     dma_init_structure.DMA_DIR                = DMA_DIR_PeripheralToMemory;
>     dma_init_structure.DMA_BufferSize         = 0xFFFF;
>      // This parameter will be configured during communication
>     dma_init_structure.DMA_Mode               = DMA_Mode_Normal;
>     DMA_Init( peripheral->rx_dma_config.stream, &dma_init_structure );
> 
>     driver->peripheral->rx_dma_config.stream->NDTR  = size; // 4096
>     driver->peripheral->rx_dma_config.stream->M0AR  = (uint32_t)data;
>     driver->peripheral->rx_dma_config.stream->CR   |= DMA_SxCR_EN;
>     USART_DMACmd( driver->peripheral->port, USART_DMAReq_Rx, ENABLE );
> 
> The driver uses DMA with circular mode, (the buffer size is 4096).
> I'm still not clear why always lost 63 chars.
> But it looks like not lwip problem but uart driver problem.

dma_init_structure.DMA_Mode = DMA_Mode_Normal;

Are you sure that's circular ? If I remember correctly STM32 shitty DMA 
controller doesn't support DMA auto restart in normal mode (next pointer 
feature), so you might lost a few bytes when restarting DMA after a DMA 
interrupt in normal mode.

Thank you Patrick for the deep analysis of the bytestream ! :)

Sylvain

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