1 files changed, 14 insertions(+), 18 deletions(-)

M bitsy/devµc.c

@@ 78,35 78,30 @@ int
 	ctlr.buf[ctlr.n++] = (uchar)ch;
 		
 	for(;;){
-		/* message hasn't started yet */
+		/* message hasn't started yet? */
 		if(ctlr.buf[0] != SOF){
-			ctlr.n = 0;
-			break;
+			p = memchr(ctlr.buf, SOF, ctlr.n);
+			if(p == nil){
+				ctlr.n = 0;
+				break;
+			} else {
+				ctlr.n -= p-ctlr.buf;
+				memmove(ctlr.buf, p, ctlr.n);
+			}
 		}
 	
-		/* if it's too short, wait */
+		/* whole msg? */
 		len = ctlr.buf[1] & 0xf;
 		if(ctlr.n < 3 || ctlr.n < len+3)
 			break;
 	
 		/* check the sum */
-		ctlr.buf[0] = ~SOF;
+		ctlr.buf[0] = ~SOF;	/* make sure we process this msg exactly once */
 		cksum = 0;
 		for(i = 1; i < len+2; i++)
 			cksum += ctlr.buf[i];
-	
-		/* ignore bad checksums */
-		if(ctlr.buf[len+2] != cksum){
-			p = memchr(ctlr.buf+1, SOF, ctlr.n);
-			if(p == nil){
-				ctlr.n = 0;
-				break;
-			} else {
-				ctlr.n -= p-ctlr.buf;
-				memmove(ctlr.buf, p, ctlr.n);
-				continue;
-			}
-		}
+		if(ctlr.buf[len+2] != cksum)
+			continue;
 	
 		/* parse resulting message */
 		p = ctlr.buf+2;


@@ 190,6 185,7 @@ _sendmsg(uchar id, uchar *data, int len)
 	serialµcputs(buf, p-buf);
 }
 
+/* the tsleep takes care of lost acks */
 static void
 sendmsgwithack(uchar id, uchar *data, int len)
 {