altos/avr: Clear SPI receive buffer before clocking new data in

I don't know why this is necessary, but the receive buffer gets
'extra' data added somehow.

Signed-off-by: Keith Packard <keithp@keithp.com>

diff --git a/src/avr/ao_spi_usart.c b/src/avr/ao_spi_usart.c
index 1996fcd9e98a9cee798aaaf3ace662c2b623924a..5ea11da6a093527a6ae96cb4caa0f8cd5ccdcaed 100644 (file)
--- a/src/avr/ao_spi_usart.c
+++ b/src/avr/ao_spi_usart.c
@@ -43,15 +43,17 @@ ao_spi_send(void __xdata *block, uint16_t len) __reentrant
 
 /* Receive bytes over SPI.
  *
 
 /* Receive bytes over SPI.
  *

- * This sets up tow DMA engines, one reading the data and another
- * writing constant values to the SPI transmitter as that is what
- * clocks the data coming in.
+ * Poll, sending zeros and reading data back

  */
 void
 ao_spi_recv(void __xdata *block, uint16_t len) __reentrant
 {
        uint8_t *d = block;
 
  */
 void
 ao_spi_recv(void __xdata *block, uint16_t len) __reentrant
 {
        uint8_t *d = block;
 

+       /* Clear any pending data */
+       while (UCSR1A & (1 << RXC1))
+               (void) UDR1;
+       

        while (len--) {
                while (!(UCSR1A & (1 << UDRE1)));
                UDR1 = 0;
        while (len--) {
                while (!(UCSR1A & (1 << UDRE1)));
                UDR1 = 0;