From: ian <ian>
Date: Sun, 9 Jan 2005 18:30:15 +0000 (+0000)
Subject: decodes packets
X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ijackson/git?a=commitdiff_plain;h=150462588db978bc325a981def557adef90ed78b;p=trains.git

decodes packets
---

diff --git a/parport/nmra-decode.pl b/parport/nmra-decode.pl
index c68b1d8..b94b281 100755
--- a/parport/nmra-decode.pl
+++ b/parport/nmra-decode.pl
@@ -16,12 +16,58 @@ sub usec_from_to ($$) {
 
 #---------- bit stream (packet) decoder ----------
 
-sub found_bit ($) {
-    my ($bit) = @_;
-}
+our ($idle_counter, $bitnum, @bytes);
 
 sub reset_packet_decoder () {
-    printf "-- restarting decoder --\n";
+    $idle_counter= 0;
+}
+
+sub packet_decoder_error ($) {
+    printf "EP (%s)\n", $_[0];
+    reset_packet_decoder();
+}
+
+sub found_bit ($) {
+    my ($bit) = @_;
+    if (defined $idle_counter) {
+	if ($bit) {
+	    $idle_counter++;
+	    printf "I%-4d\n", $idle_counter;
+	    return;
+	}
+	if ($idle_counter < 10) {
+	    packet_decoder_error("I only $idle_counter");
+	    return;
+	}
+	undef $idle_counter;
+	$bitnum= -1;
+	@bytes= ();
+    }
+    if ($bitnum<0) {
+	if ($bit) {
+	    my ($checksum,$byte);
+	    $checksum= 0;
+	    foreach $byte (@bytes) {
+		$checksum ^= hex $byte;
+	    }
+	    if ($checksum) {
+		packet_decoder_error("csum $checksum, @bytes");
+		return;
+	    }
+	    print "P @bytes\n";
+	    $idle_counter= 0;
+	    return;
+	}
+	$bitnum= 7;
+	push @bytes, 0;
+	print "F @bytes...\n";
+	return;
+    }
+    $b= hex $bytes[$#bytes];
+    $b |= ($bit << $bitnum);
+    $bytes[$#bytes]= sprintf "%02x", $b;
+    print "B @bytes($bitnum)\n";
+    $bitnum--;
 }
 
 #---------- interval -> bit decoder ----------
@@ -52,6 +98,7 @@ sub interval_mapchar ($$@) {
 }
 
 sub reset_bit_decoder () {
+    printf "-- restarting bit decoder --\n";
     undef @valuefor;
     undef $in_bit;
     $bit_phase_determined= 0;
@@ -118,19 +165,19 @@ sub found_interval ($$$) {
     }
 
     if ($bit_half) {
+	undef $in_bit;
 	if ($class eq 'U') {
-	    printf " E UU\n";
+	    printf " E UU";
 	    reset_packet_decoder();
-	} else {
-	    $bit_value= !!($class eq 'S');
-	    printf "  %d  ", $bit_value;
-	    found_bit($bit_value);
+	    return;
 	}
-	undef $in_bit;
+	$bit_value= !!($class eq 'S');
+	printf "  %d  ", $bit_value;
+	found_bit($bit_value);
     } else {
 	$in_bit= $class;
+	printf "\n";
     }
-    printf "\n";
 }
 
 #---------- interval scanner ----------