transmit between-byte spacing bits

diff --git a/hostside/nmra.c b/hostside/nmra.c
index ee5df112cf1eb45763a7836bf393f94e1c235e93..7c48f465db05b220ca9d42b16e2bb49bf3e245a4 100644 (file)
--- 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;