Re: Running and returning
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Wow, ok, that's a bug I didn't know about..? I'll post that to my v16 to-do list.
Josh.
On Thursday, November 21, 2019, 11:54:01 a.m. CST, Bob Kay via Groups.Io <rekircher@...> wrote:
All good information, and definitely
some things to play with, but the problem isn't failure to
preserve the registers but unable to modify the registers via the
"r" command after returning via VMAIN_MENU.
For instance if I place a JP 0042h (C3 42 00) in location 8000,
then issue a "g 8000" command, it comes right back to the monitor.
I am now unable to change any registers via the "R" command.? If I
type "rhl=0000" then redisplay the registers, HL hasn't changed to
0000.? Similarly for all the other registers.
-Bob
On 11/21/2019 10:09 AM, joshbensadon via Groups.Io wrote:
Bob Kircher wrote in,
"If I were to write a
program to run on the Z80MC in high memory (not?
under CPM) what is the
preferred way to return to the monitor?? I had?
been using JP 0042H ( JP
VMAIN_MENU ) but I recently discovered I can?
not change any registers
after I get back to the monitor.? I can also?
return by jumping to
location zero but I'd better be quick about hitting?
the M key else I
accidentally boot CP/M."
Great
question, worth posting to the forum.
I'm not
100% sure what I wrote and debugged but having a quick
look at the source code it appears only execution to 0000
will save the registers.
As
such, when executing the G command, the monitor places
0000 on stack as the return address.? So your code needs
to only RET to get back to the monitor.
LD HL,0 ;10
Set Default return address as 0000 (Restart/Save
Registers)
PUSH HL ;11?
?& Put on stack
Now, it
should know/resolve the restart type and not prompt you to
press M for monitor... but I'm not sure if that works...
certainly won't be the only bug in the system.? If you
really want, you can fake the M key by entering it into
the buffer yourself before returning to 0000.
Here's
a snipit of the code that saves the bit banged character
to the buffer.??
IRXD_SAVE LD?
A,H ;4 ;Fetch
received byte
LD?
HL,(RXBHEAD) ;16 ;Advance
Head Ptr of RX Buffer, Head = Head + 1
INC L ;4
LD?
(RXBHEAD),HL ;16
LD?
(HL),A ;7 ;Save
Received byte into RX Buffer
Actually, instead of faking
the M key, you can set the SOFT_RST_FLAG value (I think the
firmware might already be doing this.. but I cant' figure out
where).
When the firmware boots up,
it runs code to check this flag as follows.
If you set this flag to 0xD1 (single step return), it should return to the monitor and automatically dump the registers.
;Determine
why the CPU is executing A RESET.
;?
-Power on (RAM signature will be wrong)
;?
-F-0 Reset Switch (one of the switches will still be
pressed)
;?
-RST 0 (look for C7 at previous location given by stack)
;?
-External /RESET OR User program branches to 0000
;
;RC_TYPE
;0 COLD
RESET (NO RAM SIGNATURE)
;1 F-E
Soft Reset (SOFT_RST_FLAG = FE)
;2 Single
Step (SOFT_RST_FLAG = D1)
;3 <Ctrl>-C
(SOFT_RST_FLAG = CC)
;4 HALT
(SOFT_RST_FLAG = 76)
;5 F-0
(F or 0 key on FP still down)
;6 RST0
( M(PC-1) = C7)
;7 HARD
RESET (Default if SOFT_RST_FLAG not set)
Hopefully the RET should work
fine, but if not, it's definitely one of the things I will be
addressing in the next version of firmware.
Regards,
Josh
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