cpu/cc2538: mask length byte before checking CRC

Author: HavingaThijs

cpu/cc2538/include/cc2538_rf.h

@@ -41,6 +41,7 @@ extern "C" {
 #define CC2538_AUTOCRC_LEN          (2)
 #define CC2538_RF_FIFO_SIZE         (128)
 #define CC2538_PACKET_LENGTH_SIZE   (1)
+#define CC2538_LENGTH_BYTE_MASK     (0x7F) /**< Mask for the length byte in the packet */
 
 #define CC2538_RF_MAX_DATA_LEN (CC2538_RF_FIFO_SIZE - CC2538_PACKET_LENGTH_SIZE)
 

cpu/cc2538/radio/cc2538_rf_radio_ops.c

@@ -412,9 +412,11 @@ void cc2538_irq_handler(void)
 
     if (flags_f0 & RXPKTDONE) {
         handled_f0 |= RXPKTDONE;
-        /* CRC_OK bit is in the last byte in the RX FIFO */
-        uint8_t crc_loc = RFCORE_XREG_RXFIFOCNT - 1;
-        if (rfcore_peek_rx_fifo(crc_loc) & CC2538_CRC_BIT_MASK) {
+        /* CRC_OK bit is located in the last byte of the packet.
+         * The radio masks the length byte before filling the FIFO with the
+         * corresponding number of bytes. */
+        uint8_t pkt_len = (rfcore_peek_rx_fifo(0) & CC2538_LENGTH_BYTE_MASK);
+        if (rfcore_peek_rx_fifo(pkt_len) & CC2538_CRC_BIT_MASK) {
             /* Disable RX while the frame has not been processed */
             _disable_rx();
             /* If AUTOACK is disabled or the ACK request bit is not set */