scotty264b@... wrote:
I have Z80MC + SIO card. No FP.
If I wish to implement the single-step feature of the ZMC monitor, is it
as easy as providing a 1KHz interrupt (derived and thus sync'd with Z80
clock) and changing the "HW_LIST" at memory address 0xFF95 to 0x03 (SIO
+ FP)?
Can I use single-step in the console mode or must I use the FP?
Hi Scotty,
The CP/M DDT.COM debugger can single-step without using interrupts; thus, no front panel or timer is needed. But it requires that the program you are tracing is in RAM (i.e. not the ROM). Also, it can't trace programs in the BIOS, BDOS, or CCP.
Note that we just added DDT-V6.COM to the DISK-1 image; it is patched to change the breakpoint instruction from RST7 to RST6 so it doesn't conflict with hardware interrupts.
The Z80MC monitor uses hardware to single-step, so it can trace even programs in ROM. (That's necessary for debugging the ROM monitor, and CP/M itself.) The hardware to do this is on the Front Panel. Specifically, it needs the timer and its interrupt.
To single-step, the monitor waits for a timer interrupt. It saves the state of the Z80, and then waits "just right" so there is only time to execute *one* instruction before the next timer interrupt. *Then* it lets the Z80 execute that instruction.
The result is that the Z80 executes one instruction, and gets interrupted. The monitor can then save, examine, and change registers, memory, I/O ports, etc.
If you don't have a Front Panel, you can breadboard the timer (74HC4040, 74HC393, and two inverters). It might even be possible to simplify it to just a 74HC4020 and a couple transistors as inverters.
Lee
--
ICEs have the same problem as lightbulbs. Why innovate and make
better ones when the current ones burn out often enough to keep
you in business? -- Hunter Cressall
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
Lee Hart