## Execution commands of μCsim

### r,run,go [start [stop]]

This command starts the execution of the simulated program.

Parameters are optional. First parameter specifies start address of the execution. By default execution starts at address specified by actual value of the PC. This can be overridden by first parameter.

If second parameter is specified it places a dynamic breakpoint at specified address which stops the execution. If stop address is not given the simulator stops if it reaches a breakpoint, or the CPU accepts an interrupt and stopit option is TRUE, or fatal error occurs or stop command is used on an other console, or ENTER key is pressed on the console where the run command was issued.

If program execution is started the console is frozen it is not possible to give commands on this console to the simulator while execution is running. If it is needed to control the simulator during program execution then more consoles can be used. See using multiple consoles for more information.

Note that first instruction is executed without effect of breakpoints and simulation will be started afterwards. It means that if there is a breakpoint at start address then it will not be hit. See following example:

    $ ./s51
    ucsim 0.2.38-pre1, Copyright (C) 1997 Daniel Drotos, Talker Bt.
    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.
    > b 0x10
    Breakpoint 1 at 0x000010: MOV   R7,A
    > b 0x20
    Breakpoint 2 at 0x000020: MOV   R7,A
    > run 0x10
    Warning: maybe not instruction at 0x000010
    Simulation started, PC=0x000010
    Stop at 0x000020: (104) Breakpoint
    F 0x000020
    >

### stop

This command stops the simulation, it freezes the CPU and all the peripherals.

    $ s51 remoansi.hex
    ucsim 0.2.24, Copyright (C) 1997 Daniel Drotos, Talker Bt.
    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.
    58659 bytes read from remoansi.hex
    > g
    Simulation started
    > dr
    000000 00 01 00 14 00 00 5a 47 ......ZG
    000000 00 .  ACC= 0x47  71 G  B= 0x01   DPTR= 0x001c @DPTR= 0x47  71 G
    000001 01 .  PSW= 0x00 CY=0 AC=0 OV=0 P=0
       006f02 90 00 1e MOV   DPTR,#001e
    > stop
       006ac5 24 a5    ADD   A,#a5
    >

Simulated program is executed in background and the simulator accepts commands. If it stopped by the stop command the instruction pointed by PC is disassembled, see the dis command for description of disassembled form.

### s,step [steps]

Step command. It executes one instruction without effect of breakpoints.

The optional parameter can be used to specify number of instructions to execute. Note that breakpoints will stop the execution after the first instruction.

    $ s51 remoansi.hex
    ucsim 0.2.12, Copyright (C) 1997 Daniel Drotos, Talker Bt.
    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.
    58659 bytes read from remoansi.hex
    > s
    000000 00 00 00 00 00 00 00 00 ........
    000000 00 .  ACC= 0x00   0 .  B= 0x00   DPTR= 0x0000 @DPTR= 0x00   0 .
    000000 00 .  PSW= 0x00 CY=0 AC=0 OV=0 P=0
       000160 c2 90    CLR   P1.0
    >

After execution of actual instruction pointed by PC (or all instructions specified by the optional parameter) the step command dumps out the register set.

### n,next

Execute until next instruction is reached. This command is similar to step command described above but if actual instruction to execute is a subroutine call the next command places a dynamic breakpoint after the call instruction and starts to execute the subroutine. If the subroutine is infinite the breakpoint set by next will never reached. It can be a dangerous situation because the execution started by the next command can not be stopped interactively. But it can be stopped by other breakpoints.

    $ s51 remoansi.hex
    ucsim 0.2.12, Copyright (C) 1997 Daniel Drotos, Talker Bt.
    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.
    58659 bytes read from remoansi.hex
    > run 0 0x172
       000172 79 04    MOV   R1,#04
    > dis 0x172 0 5
       000170 7f 00    MOV   R7,#00
       000172 79 04    MOV   R1,#04
       000174 12 0d b8 LCALL 0db8
       000177 0f       INC   R7
       000178 d9 fa    DJNZ  R1,0174
       00017a 75 0b 00 MOV   0b,#00
    > n
    000000 00 04 00 00 00 00 00 00 ........
    000000 00 .  ACC= 0x00   0 .  B= 0x00   DPTR= 0x0000 @DPTR= 0x00   0 .
    000004 00 .  PSW= 0x00 CY=0 AC=0 OV=0 P=0
       000174 12 0d b8 LCALL 0db8
    > n
    000000 00 04 00 00 00 00 00 00 ........
    000000 00 .  ACC= 0x00   0 .  B= 0x00   DPTR= 0x0167 @DPTR= 0x00   0 .
    000004 00 .  PSW= 0x00 CY=0 AC=0 OV=0 P=0
       000177 0f       INC   R7
    >

### pc [address]

Using this command without any parameter it simply dumps out instruction pointed by the PC. Specify address if you want to set the PC.

    $ s51
    S51 0.1.5, Copyright (C) 1997 Daniel Drotos, Talker Bt.
    S51 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.
    > pc
     * 000000 ff       MOV   R7,A
    > pc 123
     * 00007b ff       MOV   R7,A
    > sopt debug t
    > pc 32
    Warning: maybe not instruction at 000020
     * 000020 ff       MOV   R7,A
    >