ajparent1/kb1gmx wrote:
Having a [Front Panel] should be seamless, least it was on my old
Altair when it behaved. There is no reason why CP/M should not run
with a FP. Also the blinkin lights thing.
Yes; the blinkin-lights are an important feature of a FP. "What are all those blinking lights doing, son?" "Impressing you, dad!"
A hardware front panel shouldn't have any effect on the computer. But a software-driven front panel (like the Z80MC or a Heath H8) has to interact. It needs a program in memory to run it, and an interrupt to periodically update the blinkin-lights. The interrupt routine requires time, and that there be a working stack, among other things.
The Z80MC uses RST7 for its timer/serial/front panel interrupt. We just discovered that CP/M's DDT also uses RST7 for breakpoints. Thus they conflict; so DDT will crash the system!
There are a couple ways to fix this:
1. Software: I've been looking at the DDT source, and there is an option to use RST6 instead of RST7. DRI apnote #7 (attached) describes the procedure for patching DDT to use RST6. It says to change address 01EB from FF to F7.
But, Bob Kircher reports that his copy of DDT had the FF at 01EC (not 01EB). So he patched to 01EC from FF to F7; and it worked. :-)
2. Hardware: It is also possible to move the hardware interrupt from RST7 to some other interrupt. But this requires some cuts-n-patches, plus some software changes to the ROM and BIOS to account for it. So I think we'll save that for a future revision.
DDT loads to 100H then senses the base of BDOS and relocated
to under that so the space from 100h to below DDT is available for
user programs that would nominally be at loaded at 100H when
finished or debugged.
Yes; DDT is a *very* clever program! The source has been published ro all to see. Besides relocating itself, it can also allow the program it is debugging to overlay parts of it, and still keep the remaining parts working.
Lee
--
There is a computer disease that anybody who works with computers knows
about. It's very serious, and interferes completely with your work. The
trouble with computers is that you 'play' with them! (Richard Feynman)
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
Lee Hart