Motorola USB08 Betriebsanleitung PDF herunterladen (Seite 60)

8.25 Trace T

Format:

T[Repeats] [StartAddress|*]

Command to trace a program in MCU controlled memory. If no explicit start address is specified, then

tracing will begin at the current value of the 'T/G' address. Repeats is an optional number which

specifies how many times the command is to be repeated. Note that repeats is specified as a decimal

number, unlike all other values which are entered in hexadecimal. The value of 'Repeats' follows the

letter T without a gap. When the command is given, Xplor8 carries out the following operations:

1. The instruction at the starting address is disassembled to discover the address of the following

instruction (or instructions if there is the possibility of a branch);

2. Xplor8 determines which is the effective following instruction, based on the opcode, the

contents of the CCR, and on other information as appropriate.

3. A breakpoint is then written to MCU memory to 'catch' the program after execution of the

current instruction. This breakpoint is displayed in the Start/Break Point window (page 22);

4. The MCU is set running at the current instruction, the status line is updated to read 'Tracing',

and the instruction at the trace starting address appears in the breakpoint display in green;

5. As soon as the MCU stops at a breakpoint, that breakpoint is highlighted in red in the

breakpoint display, the breakpoint information is copied to the output window, and the status

line reverts to: 'Monitor Mode'. If populated, the watch window display is also updated.

6. The above processes are repeated if 'Repeats' is specified as greater than 1.

The Xplor8 internal trace starting address, T/G, and the default list and unassemble address, L/U, are

also updated to show where the last trace instruction has stopped; so issuing the 'T' command alone

will continue tracing from where the previous trace operation halted.

Care needs to be taken if tracing is begun at an RTS or RTI instruction if program execution has not

arrived at that point by itself, e.g. as the result of issuing a Go (Run) command (page 48). This is so

because the next address at which tracing (or stepping over - see the Step Over command on page 61)

will halt is computed from the preceding value on the stack: this value will be quite arbitrary if tracing

is begun 'out of the blue' at either of these instructions.

Examples:

T 800B Begins tracing with the instruction at address $800B

T3 Begins tracing at the current value of 'T/G' address and traces the next three

instructions

1 2 ... 55 56 57 58 59 60 61 62 63 64 65 ... 99 100

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Motorola USB08 Betriebsanleitung Seite 60