Do more RX checks in the IRQ handler.

diff --git a/firmware/modbus.c b/firmware/modbus.c
index 00a9370a05bdaa872ce14b38f95de35d194d275b..e45f5f0f7ba9064472ba9ff6510ac5e4fdc5df3b 100644 (file)
--- a/firmware/modbus.c
+++ b/firmware/modbus.c
@@ -169,18 +169,10 @@ uint8_t modbus_poll()
                if (transmitting)
                        return 0;
 
-               if (buf_len == 0) // nothing received yet
-                       return 0;
-
                if (get_clock() - last_rx < REQ_TIMEOUT) // still receiving
                        return 0;
 
-               if (buf_len < 4) { // too short
-                       buf_len = 0;
-                       return 0;
-               }
-
-               if (buffer[0] != mb_unit_id) { // not for myself
+               if (buf_len < 4) { // too short (or not for us)
                        buf_len = 0;
                        return 0;
                }
@@ -241,16 +233,28 @@ uint8_t modbus_poll()
 ISR(USART_RX_vect)
 {
        uint8_t rx_byte = UDR0;
+       clock_t now = get_clock();
+
+       if (transmitting) // how did we get here? discard it
+               goto out;
 
-       if (transmitting) // discard it
-               return;
+       if (buf_len && buffer[0] != mb_unit_id) // not for us
+               goto out;
 
-       buffer[buf_len] = rx_byte;
+       if (buf_len == BUFSIZE) { // overrun - discard the packet
+               buffer[0] = 0xFF;
+               buf_len = 1;
+               goto out;
+       }
 
-       if (buf_len + 1 < BUFSIZE) // ignore overruns
-               buf_len++;
+       if (now - last_rx >= REQ_TIMEOUT) { // new packet; start over
+               buf_len = 0;
+       }
 
-       last_rx = get_clock();
+       // TODO: we can probably calculate the CRC here as well
+       buffer[buf_len++] = rx_byte;
+out:
+       last_rx = now;
 }
 
 ISR(USART_TX_vect)