Commit 8a99bd0d authored May 04, 2020 by Benjamin Valentin Committed by Kumar Gala May 05, 2020

drivers: spi: spi_sam0: fix spi_sam0_fast_txrx()



The optimisation in `spi_sam0_fast_txrx()` is broken, loading
two bytes into the `DATA` register in rapid succession will lose
one byte.

This can be observed by running `tests/drivers/spi/spi_loopback`.
The test will get stuck in `spi_sam0_fast_txrx()` forever waiting
for the final byte.

Undo this small optimisation and only load the next byte into the
`DATA` register after the response has been received.

This fixes `tests/drivers/spi/spi_loopback`.

Signed-off-by: Benjamin Valentin <benpicco@googlemail.com>

parent 52a950bb

drivers/spi/spi_sam0.c

+3 −5

Original line number	Diff line number	Diff line
		@@ -269,17 +269,15 @@ static void spi_sam0_fast_txrx(SercomSpi *regs,
		regs->DATA.reg = *tx++;

		while (tx != txend) {
		/* Load byte N+1 into the transmit register. TX is
		* single buffered and we have at most one byte in
		* flight so skip the DRE check.
		*/
		regs->DATA.reg = *tx++;

		/* Read byte N+0 from the receive register */
		while (!regs->INTFLAG.bit.RXC) {
		}

		*rx++ = regs->DATA.reg;

		/* We just received the response, send the next byte */
		regs->DATA.reg = *tx++;
		}

		/* Read the final incoming byte */

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