Breakpoints commands of µCsim

Commands of µCsim to manage breakpoints

Two kinds of breakpoint can be used: fetch and event breakpoint. Fetch breakpoints are classical breakpoints. They can be placed at any instruction in the code memory. Breakpoint will be hit if the CPU fetches instruction code from the memory location specified by the breakpoint. Only fetching of first byte of the instruction hits the breakpoint. If the execution reaches a breakpoint it stops before the instruction at location specified by the breakpoint would be executed.

Event breakpoints are special ones. They cause stop of execution if event specified by the breakpoint occurs. Event can be a read or a write operation on any address space location. An event breakpoint stops execution after specified event occurred.

Every breakpoint can be fix (permanent) or dynamic (temporary). Dynamic breakpoints are automatically removed when they reached. Some commands place dynamic fetch breakpoints into the code, for example go or next.

A hit count can be associated to any breakpoint. This hit number specifies how many times the breakpoint must be hit before it causes the execution to stop. This hit number is 1 by default.

break addr [hit] [if expression]
break memory_type r|w addr [hit] [if expression]

tbreak addr [hit] [if expression]
tbreak memory_type r|w addr [hit] [if expression]

Set fetch or event breakpoint. The command specifies whether the breakpoint will be fix (break) or dynamic (temporary) (tbreak).

Fetch or event breakpoint can be defined. First form defines fetch while second form defines event breakpoint.

Fetch breakpoint: First parameter specifies address where the breakpoint must be placed to. It should be address of an instruction. If a variable is used here, it must point to an address space location, otherwise an event breakpoint is created.
Second parameter is optional and it specifies the hit number. It is 1 by default.
Event breakpoint: First parameter specifies class name of memory where we are going to watch for en event. Class names of memories can be checked by info memory command.
Second parameter specifies the event. It can be r to specify read operation or w which means write operation.
Remaining parameters are address of watched memory location and an optional hit number (1 by default).

Last parameter can be the if keyword, followed by an expression. If it is specified, the expression is evaluated at every breakpoint hit and the breakpoint will be accepted only when the expression evaluates to TRUE.

$ ucsim_51
uCsim 0.9.10, Copyright (C) 1997 Daniel Drotos.
uCsim comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
This is free software, and you are welcome to redistribute it
under certain conditions; type `show c' for details.
0> load "remo.hex"
Loading from remo.hex
55755 words read from remo.hex
0> dc 0 0x10
0x0000    02 01 60 LJMP   0x0160
0x0003    02 00 3c LJMP   0x003c
0x0006    ff       MOV    R7,A
0x0007    ff       MOV    R7,A
0x0008    ff       MOV    R7,A
0x0009    ff       MOV    R7,A
0x000a    ff       MOV    R7,A
0x000b    02 2f 74 LJMP   0x2f74
0x000e    ff       MOV    R7,A
0x000f    ff       MOV    R7,A
0x0010    ff       MOV    R7,A
0> break 0x160
Breakpoint 1 at 0x000160 (cond="")
0x0160 F  c2 90    CLR    0x900x90 <P1>.0
0> tbreak 8 2
Breakpoint 2 at 0x000008 (cond="")
0x0008 D  ff       MOV    R7,A
0> run
Simulation started, PC=0x000000

Stop at 0x000160: (104) Breakpoint
     R0 R1 R2 R3 R4 R5 R6 R7
     41 58 fc c9 8b bc 95 6b
@R0 76 v  ACC= 0x00   0 .  B= 0x00
@R1 73 s  PSW= 0x00 CY=0 AC=0 OV=0 P=0
SP 0x07 -> 6b 95 bc 8b c9 fc 58 41
   DPTR= 0x0000 @DPTR= 0x83 131 .
0x0160 F  c2 90    CLR    0x900x90 <P1>.0
F 0x000160
Simulated 24 ticks (2.170e-06 sec)
Host usage: 0.000003 sec, rate=0.700171
0>

Breakpoint hits can be made more noticeable by printing a beep character on the console. This function can be turned on by setting the option beep_break (FALSE by default).

clear [addr...]

Delete fetch breakpoint. Parameter specifies address of breakpoint. If there is no breakpoint specified at given address this command prints out a warning message.

If parameter is not given then breakpoint at current PC will be deleted if it exists. If more than one address is specified then all breakpoints at specified addresses will be deleted.

$ ucsim_51
uCsim 0.9.10, Copyright (C) 1997 Daniel Drotos.
uCsim comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
This is free software, and you are welcome to redistribute it
under certain conditions; type `show c' for details.
0> load "remo.hex"
Loading from remo.hex
55755 words read from remo.hex
0> break 0x160
Breakpoint 1 at 0x000160 (cond="")
0x0160 F  c2 90    CLR    0x900x90 <P1>.0
0> tbreak 8 2
Breakpoint 2 at 0x000008 (cond="")
0x0008 D  ff       MOV    R7,A
0> info break
Num Type       Disp Hit   Cnt   Address  Cond
1   fetch      keep 1     1     0x000160 true  
2   fetch      del  2     2     0x000008 true  
0> clear 160
No breakpoint at 0x0000a0
0> clear 0x160
0> i b
Num Type       Disp Hit   Cnt   Address  Cond
2   fetch      del  2     2     0x000008 true  
0>

delete [number...]

Delete breakpoint(s) by its number.

If parameter is not used then all breakpoints are deleted.

commands breakpoint-nr [script]

Attach a script to a breakpoint. Breakpoint number can be omitted if only one breakpoint exists. Breakpoint numbers can be checked by info breakpoint command. The script is a command or a list of commands separated by a semicolon (;) character. It will be executed when the specified breakpoint is accepted. Whether the text of the script is printed before execution is controlled by the option echo_script, which is FALSE by default. See set option command how to set it. If script is not used, breakpoint command will be deleted from the specified breakpoint.

display [[/format] expr]

Set expression to be displayed when simulation stops on a breakpoint.

/format option can be used to specify print format for the expression. For meaning of the options, see expression command.

If no expr argument is given, all defined expressions are listed and evaluated and values are printed.

$ ucsim_51
uCsim 0.9.10, Copyright (C) 1997 Daniel Drotos.
uCsim comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
This is free software, and you are welcome to redistribute it
under certain conditions; type `show c' for details.
0> load "remo.hex"
Loading from remo.hex
55755 words read from remo.hex
0> disp R7
0> disp ACC
0> break 0x9f9
Breakpoint 1 at 0x0009f9 (cond="")
0x09f9 F  c2 a9    CLR    0xa90xa8 <IE>.1
0> display
1: R7 = 107
2: ACC = 0
0> run
Simulation started, PC=0x000000

Stop at 0x0009f9: (104) Breakpoint
     R0 R1 R2 R3 R4 R5 R6 R7
     41 04 fc c9 8b bc 00 00
@R0 76 v  ACC= 0x00   0 .  B= 0x00
@R1 8b .  PSW= 0x00 CY=0 AC=0 OV=0 P=0
SP 0x24 -> 01 77 1d 84 43 31 94 d0
   DPTR= 0x0000 @DPTR= 0x83 131 .
0x09f9 F  c2 a9    CLR    0xa90xa8 <IE>.1
F 0x0009f9
Simulated 180 ticks (1.628e-05 sec)
Host usage: 0.000010 sec, rate=1.625397
1: R7 = 0
2: ACC = 0
0>

undisplay [nr]

Remove selected, or all (if no nr argument is specified) expression from display list. To check out id number of an expression, use display command without arguments.