/** Returns a lower bound on the number of bytes in the DMA receive buffer.
* Also checks for buffer overrun conditions.
* \param s The USART DMA state structure.
*/
u32 usart_n_read_dma(usart_rx_dma_state* s)
{
s32 n_read = s->rd_wraps * USART_RX_BUFFER_LEN + s->rd;
s32 n_written = (s->wr_wraps + 1) * USART_RX_BUFFER_LEN - \
DMA_SNDTR(s->dma, s->stream);
s32 n_available = n_written - n_read;
if (n_available < 0)
/* This strange and rare case occurs when NDTR has rolled over but the flag
* hasn't been raised yet and thus n_wraps hasn't been incremented in the
* ISR. Simply return 0 this time and the next time this function is called
* (or at some point) the interrupt will have been triggered and the number
* of bytes available in the buffer will be a sane amount. */
n_available = 0;
else if (n_available > USART_RX_BUFFER_LEN) {
/* If greater than a whole buffer then we have had an overflow. */
printf("ERROR: DMA RX buffer overrun\n");
n_available = 0;
s->errors++;
/* Disable and re-enable the DMA channel to get back to a known good
* state */
usart_rx_dma_disable(s);
usart_rx_dma_setup(s, s->usart, s->dma, s->stream, s->channel);
}
return n_available;
}
/** Disable all USARTs. */
void usarts_disable()
{
/* Disable DMA channels. */
/* Disable all USARTs. */
if (!all_uarts_enabled)
return;
usart_tx_dma_disable(&ftdi_state.tx);
usart_rx_dma_disable(&ftdi_state.rx);
usart_disable(USART6);
usart_tx_dma_disable(&uarta_state.tx);
usart_rx_dma_disable(&uarta_state.rx);
usart_disable(USART1);
usart_tx_dma_disable(&uartb_state.tx);
usart_rx_dma_disable(&uartb_state.rx);
usart_disable(USART3);
}
