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To execute a single instruction use the command step
.
This will execute the instruction pointed to by the current value of the
program counter register.
In the example of Figure 5.3, prior to the step
command
the program counter is pointing the instruction at address 0x1703 which is
a ‘tfr’ instruction. This causes the contents of register Y to
be copied into register D6.
In addition, program counter will be advanced to the next instruction.
The new contents of the registers can be seen in the second call to
read-all-regs
.
> disassemble 0x1700 0x24 00001700 <.data>: 1700: bc 06 cc clr.b 1740 1703: 9e 96 tfr y, d6 1705: 5e 00 ff ff and d6, #16777208 1709: f8 170a: 9e 90 tfr y, d2 170c: 58 00 07 and d2, #7 170f: dd b8 neg.w d2 1711: 9e 01 tfr d2, d3 1713: 9e 69 tfr d6, y 1715: 0b 11 80 0b tbeq d3, *+11 1719: 1c 99 89 mov.b (d3,y), (d3,x) 171c: 31 inc d3 171d: 20 ff f8 bra *-8 1720: 08 88 lea x, (d2,x) 1722: 67 be add d7, d6 > read-all-regs D0: 00 D1: 00 D2: FFFF D3: 0000 D4: 0000 D5: 0000 D6: 00A8207E D7: 00000000 X: 000000 Y: FE0091 SP: 003000 PC: 001703 CCW: u----000SX-Inzvc > step > read-all-regs D0: 00 D1: 00 D2: FFFF D3: 0000 D4: 0000 D5: 0000 D6: 00FE0091 D7: 00000000 X: 000000 Y: FE0091 SP: 003000 PC: 001705 CCW: u----000SX-InzvcFigure 5.3: Using the
step
command to execute an instruction. This instruction causes the PC and D6 register be updated.
Next: Writing to CPU registers, Previous: Examining CPU registers, Up: Debugging [Contents][Index]