echo now _almost_ works, it gets right-shifted by 8

firmware/shared/spi.c

@@ -127,14 +127,16 @@ void spi_sla_handle_packet(){
         // TODO: make slave not hangup in case of partial read
 	uint8_t opcode, addr, do_write;
 	uint16_t data, newdata;
-    opcode = readbuf[1];
-    addr = readbuf[2];
-	data = (readbuf[3]<<8)&0xff | readbuf[4];
+	writebuf[0] = 0; // generate invalid replies, so no inconsistent packets
+						// are sent.
+    opcode = readbuf[0];
+    addr = readbuf[1];
+	data = (readbuf[2]<<8)&0xff | readbuf[3];
 	newdata = spi_proto_slaveaction(opcode, addr, data);
-	writebuf[0]=opcode;
 	writebuf[1]=addr;
 	writebuf[2]=(newdata>>8)&0xff;
 	writebuf[3]=(newdata)&0xff;
+	writebuf[0]=opcode; // set opcode last to validate packet (it's a kind of locking)
 }
 
 
@@ -151,8 +153,8 @@ ISR(SPI_STC_vect){
 
 	
 
-ISR(PCINT0_vect){
-    if(SPI_SSIN & _BV(SPI_SS_PIN)){
+ISR(PCINT0_vect){ // SS-line changed
+    if(SPI_SSIN & _BV(SPI_SS_PIN)){ // SS-line was actually released
         pos=0;
         SPCR &= ~(_BV(SPIE));
         sei();

firmware/shared/spi_proto.c

@@ -16,10 +16,11 @@ uint16_t spi_master_transceive(uint8_t opcode, uint8_t addr, uint16_t value)
 		spi_mst_start_packet();
 		spi_mst_write_read(5,mst_buf);
 		spi_mst_end_packet();
-	} while(mst_buf[1] == 0); // wait for echoed opcode
+	} while(mst_buf[1] =! opcode || mst_buf[2] != addr); // wait for echoed opcode
+	//TODO: validate opcode and addr
 
 	// bytes from slave are received shifted right by one
-	return (mst_buf[3] << 8) | mst_buf[4];
+	return ((mst_buf[3] << 8) | mst_buf[4]);
 }
 
 
@@ -58,12 +59,8 @@ void call_func(uint8_t number)
 uint16_t spi_proto_slaveaction(uint8_t opcode, uint8_t addr, uint16_t data) {
 	uint16_t retval = 0;
 	switch(opcode){
-		case 0:
-			retval = data;
-			break;
 		case 1:
-			//TODO
-			retval = 0;
+			retval = data;
 			break;
 		case 2:
 			retval = (*spi_proto_globals8[addr]);
@@ -79,6 +76,13 @@ uint16_t spi_proto_slaveaction(uint8_t opcode, uint8_t addr, uint16_t data) {
 			break;
 		case 6:
 			(*spi_proto_funcs[addr])();
+			//TODO: prevent a function from being run several times because the message gets repeated.
+			break;
+		case 7:
+			//TODO
+			retval = 0;
+			break;
+		default:
 			break;
 	}
 	return retval;