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H316: Improve IMP error recovery when a remote host is restarted.

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This commit is contained in:
Mark Pizzolato 2013-12-02 12:00:48 -08:00
parent 33248778cf
commit 8810571d7e
1 changed files with 18 additions and 3 deletions
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21
H316/h316_udp.c
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@ -31,6 +31,7 @@
26-Jun-13 RLA Rewritten from TCP version
26-Nov-13 MP Rewritten to use TMXR layer packet semantics thus
allowing portability to all simh hosts.
2-Dec-13 RLA Improve error recovery if the other simh is restarted
OVERVIEW
@ -341,6 +342,7 @@ t_stat udp_send (DEVICE *dptr, int32 link, uint16 *pdata, uint16 count)
t_stat udp_set_link_loopback (DEVICE *dptr, int32 link, t_bool enable_loopback)
{
// Enable or disable the local (interface) loopback on this link...
if ((link < 0) || (link >= MAXLINKS)) return SCPE_IERR;
if (!udp_links[link].used) return SCPE_IERR;
if (dptr != udp_links[link].dptr) return SCPE_IERR;
@ -423,12 +425,25 @@ int32 udp_receive (DEVICE *dptr, int32 link, uint16 *pdata, uint16 maxbuf)
// this packet is greater than that, then we must have missed one or two
// packets. In that case we MUST update rxsequence to match this one;
// otherwise the two ends could never resynchronize after a lost packet.
//
// And there's one final complication to worry about - if the simh on the
// other end is restarted for some reason, then his sequence numbers will
// reset to zero. In that case we'll never recover synchronization without
// special efforts. The hack is to check for a packet sequence number of
// zero and, if we find it, force synchronization. This improves the
// situation, but I freely admit that it's possible to think of a number of
// cases where this also fails. The only absolute solution is to implement
// a more complicated system with non-IMP control messages exchanged between
// the modem emulation on both ends. That'd be nice, but I'll leave it as
// an exercise for later.
pktseq = ntohl(pkt.sequence);
if (pktseq < udp_links[link].rxsequence) {
if ((pktseq == 0) && (udp_links[link].rxsequence != 0)) {
sim_debug(IMP_DBG_UDP, dptr, "link %d - remote modem restarted\n", link);
} else if (pktseq < udp_links[link].rxsequence) {
sim_debug(IMP_DBG_UDP, dptr, "link %d - received packet out of sequence 1 (expected=%d received=%d\n", link, udp_links[link].rxsequence, pktseq);
continue;
continue; // discard this packet!
}
if (pktseq != udp_links[link].rxsequence) {
else if (pktseq != udp_links[link].rxsequence) {
sim_debug(IMP_DBG_UDP, dptr, "link %d - received packet out of sequence 2 (expected=%d received=%d\n", link, udp_links[link].rxsequence, pktseq);
}
udp_links[link].rxsequence = pktseq+1;