From: ian <ian>
Date: Wed, 5 Jan 2005 00:20:21 +0000 (+0000)
Subject: transmit between-byte spacing bits
X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ijackson/git?a=commitdiff_plain;h=a3002bdc7d9417deb1eb33e3fa68f8294c2215b7;p=trains.git

transmit between-byte spacing bits
---

diff --git a/hostside/nmra.c b/hostside/nmra.c
index ee5df11..7c48f46 100644
--- a/hostside/nmra.c
+++ b/hostside/nmra.c
@@ -6,21 +6,26 @@
 
 void nmra_transmit(const Byte *nmra_packet, int length) {
   Byte encoded[COMMAND_ENCODED_MAX], *encp;
-  unsigned working;
+  unsigned working, newbits;
   int working_qty;
 
+  assert(length > 0);
   assert(length <= NMRA_PACKET_MAX);
   encp= encoded;
   working= 0xfffc;   /* 16-bit temp register.  Top working_qty bits    */
-  working_qty= 14;   /*  are some data bits to encode, rest are clear. */
+  working_qty= 15;   /*  are some data bits to encode, rest are clear. */
+  /* we start with the 14-bit preamble and the packet start bit */
   for (;;) {
     assert(working_qty >= 0);
     if (working_qty < 7) {
       if (length > 0) {
 	/* plonk new data bits just to right of old data bits */
-	working |= (*nmra_packet++ << (8-working_qty));
 	length--;
-	working_qty += 8;
+	newbits= *nmra_packet++;
+	newbits <<= 1;
+	newbits |= !length; /* 9 bits, bottom one is `end of packet' */
+	working |= (newbits << (7-working_qty));
+	working_qty += 9;
       } else if (!working_qty) {
 	/* all done */
 	break;