version 0.4

2 files changed, 49 insertions, 1 deletions

diff --git a/doc/mdk_gstart.texi b/doc/mdk_gstart.texi
index 25764a0..70ded05 100644
--- a/doc/mdk_gstart.texi
+++ b/doc/mdk_gstart.texi
@@ -445,6 +445,7 @@ MIX >
 @end example
 
 Other useful commands for debugging are @code{tracing} (which turns on
-tracing of executed intructions) and @code{weval} (which evaluates
+tracing of executed intructions), @code{pbt} (which prints a backtrace
+of executed instructions) and @code{weval} (which evaluates
 w-expressions on the fly). For a complete description of all available
 MIX commands, @xref{mixvm}.
diff --git a/doc/mdk_mixvm.texi b/doc/mdk_mixvm.texi
index f5538cd..480abbc 100644
--- a/doc/mdk_mixvm.texi
+++ b/doc/mdk_mixvm.texi
@@ -373,6 +373,53 @@ actual MIXAL code that was compiled into the executed instruction. The
 tracing behaviour is stored as a configuration parameter in @file{~/.mdk}.
 @end deffn
 
+@deffn {debug command} pbt [INS_NUMBER]
+This command prints a backtrace of executed instructions. Its optional
+argument @var{ins_number} is the number of instructions to print. If it
+is omitted or equals zero, all executed instructions are printed. For
+instance, if you compile and load the following program (@file{bt.mixal}):
+
+@example
+    ORIG 0
+BEG JMP *+1
+    JMP *+1
+FOO JMP BAR
+BAR HLT
+    END BEG
+@end example
+
+@noindent
+you could get the following traces:
+
+@example
+MIX > load bt
+Program loaded. Start address: 0
+MIX > next
+MIX > pbt 
+#0      BEG     in bt.mixal:2
+MIX > next
+MIX > pbt
+#0      1       in bt.mixal:3
+#1      BEG     in bt.mixal:2
+MIX > run
+Running ...
+... done
+MIX > pbt 3
+#0      BAR     in bt.mixal:5
+#1      FOO     in bt.mixal:4
+#2      1       in bt.mixal:3
+MIX > pbt
+#0      BAR     in bt.mixal:5
+#1      FOO     in bt.mixal:4
+#2      1       in bt.mixal:3
+#3      BEG     in bt.mixal:2
+MIX >
+@end example
+
+Note that the executed instruction trace gives you the label of the
+executed line or, if it has no label, the its address.
+@end deffn
+
 As you have probably observed, @code{mixvm} prints timing statistics
 when running programs. This behaviour can be controlled using the
 @code{timing} command (@pxref{Configuration commands}).