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Appendix A shows the disassembled part of the timeout routine.
Appendix B shows an assembler source for the timeout routine.
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| Amstrad, June 1986 | Page 1 of 5 |
CP/M DEVICE TIMEOUTS
The BIOS within CP/M Plus attempts to prevent the System "locking up" completely when a non-existent device is referenced by means of a timeout.
So, for example, if [CTRL] P were typed accidentally when there was no printer available, after approximately 10 seconds the BIOS will recognise that there is no printer responding and will produce a status message along the lines of :
LPT not ready - Retry, Ignore or Cancel ?
This allows you to either switch a printer on-line then Retry, or rectify the error by pushing C for cancel (which then directs all printer output to a null device).
Unfortunately, some printers take such a long time form feeding (or sheet feeding) that the BIOS times out before the operation has been finished so that R must be hit repeatedly.
The length of this timeout may be extended by modifying the '.EMS' CP/M system file.
This can be done using the programming utility SID.COM, that is to be found on the "Programming Utilities" side of the system discs.
CP/M Plus has been implemented on both the CPC 6128 and the PCW 8256.
Consequently, there are different instructions for modifying the system file depending on which machine you have.
As well as setting the timeout to a longer period it can also be made infinite.
Continued
| Amstrad, June 1986 | Page 2 of 5 |
THE FOLLOWING IS FOR 6128 ONLY
1) To set timeout to approximately 15 seconds
In order to increase the timeout period to approximately 15 seconds, the following procedure should be followed :
Start CP/M Plus from the side 1 system disc.
Once this has loaded, switch across to the programming Utilities on side 2.
Then type :
SID
Once the program has loaded, remove this disc and re-insert side 1 (the side from which CP/M was originally loaded).
Now type :
RC10CPM3.EMS
This reads in the CP/M system file so that you can modify it.
Only two bytes need be changed and that is accomplished with the following :
S2673
The screen will show :
2673 10
Type in :
FF
The screen will now show :
2674 A4
Type in :
FF
. {a full stop ends input}
Once these changes have been made the new version may be written back to disc using the following command :
WC10CPM3.EMS,0100,64FF
This modification has no other side-effect.
Continued ....
| Amstrad, June 1986 | Page 3 of 5 |
2) To set the timeout to an infinite period
SID is loaded and the system file read in as described above.
The actual modifications to be made are, however, a little more convoluted.
First type :
S2580
The machine will respond with :
2580 90
Type the following :
E7
3F
.
Now type :
S23E7
78
FE
01
C2
90
3D
F6
FF
C9
.
And finally write the code out using :
WC10CPM3.EMS,0100,64FF
In the above, two bytes have been highlighted.
These can be changed to a number of possible values depending on which devices the timeout is to be set infinite for.
| FE 01 | (as above) | set | infinite | timeout for PRINTER |
| | normal | timeout for SERIAL PORT |
| FE 02 | set | normal | timeout for PRINTER |
| | infinite | timeout for SERIAL PORT |
| E6 00 | set | infinite | timeout for PRINTER |
| | infinite | timeout for SERIAL PORT |
WARNING: IF THIS PATCH IS USED THEN A PRINTER/SERIAL DEVICE MUST BE FITTED WHEN CP/M IS USED OR IT WILL LOCK_UP.
Continued ....
| Amstrad, June 1986 | Page 4 of 5 |
THE FOLLOWING IS FOR 8256 ONLY
1) To set timeout to approximately 15 seconds
In order to increase the timeout period to approximately 15 seconds, the following procedure should be followed :
Start CP/M Plus from the side 2 System disc.
Once this has loaded, switch across to the programming utilities on side 3.
Then type :
SID
Once the program has loaded, remove this disc and re-insert side 2 (the side from which CP/M was originally loaded).
Now type :
RJ14CPM3.EMS
This reads in the CP/M system file so that you can modify it.
Only two bytes need be changed and that is accomplished with the following :
S6F73
The screen will show :
6F73 10
Type in :
FF
The screen will now show :
6F74 A4
Type in :
FF
. {a full stop ends input}
Once these changes have been made the new version may be written back to disc using the following command :
WJ14CPM3.EMS,0100,A0FF
This nodification has no other side-effect.
Continued ....
| Amstrad, June 1986 | Page 5 of 5 |
2) To set the timeout to an infinite period
SID is loaded and the system file read in as described above.
The actual modifications to be made are, however, a little more convoluted.
First type :
S6E80
The machine will respond with :
6E80 90
Type the following :
A5
BD
.
Now type :
S6BA5
78
FE
01
C2
90
BA
F6
FF
C9
.
And finally write the code out using :
WJ14CPM3.EMS,0100,A0FF
In the above, two bytes have been highlighted.
These can be changed to a number of possible values depending on which devices the timeout is to be set infinite for.
| FE 01 | (as above) | set | infinite | timeout for LPT |
| | normal | timeout for SIO & CEN |
| FE 02 | set | infinite | timeout for SIO |
| | normal | timeout for LPT & CEN |
| FE 03 | set | infinite | timeout for CEN |
| | normal | timeout for LPT & SIO |
| E6 00 | set | infinite | timeout for LPT |
| | infinite | timeout for SIO |
| | infinite | timeout for CEN |
WARNING: IF THIS PATCH IS USED THEN A PRINTER/SERIAL DEVICE MUST BE FITTED WHEN CP/M IS USED OR IT WILL LOCK_UP.
The End
APPENDIX A
Disassembled part of the .EMS file:
Timeout delay routine in CP/M file .EMS
; File : j14gcpm3.ems
6F72 LD HL,A410 ; Set delay
6F75 LAB0: CALL BAD8 ; Test device ready
6F78 JR NZ,0A=LAB1 ; Ok, well done
6F7A DEC HL ; Count down delay
6F7B LD A,H
6F7C OR L
6F7D JR NZ,F6=LAB0 ; Test done
6F7F CALL 39C3 ; Process error if time out
6F82 SBC A,L
6F83 CALL 9D62
6F86 LAB1: JP A0F0 ; Proceed
APPENDIX B
Assembler routine for extending the timeouts:
BIOS timeout fix MACRO-80 3.44 09-Dec-81 PAGE 1
title BIOS timeout fix
.comment :
The follwing patch is made to set the timeout
to a longer period.With this patch the timeout
message appears after approximately 20 seconds.
Written by Werner Cirsovius
Hohe Weide 44
D-2000 Hamburg 20
Germany
Many thanks to AMSTRAD who sent me the
principle paper about CP/M device timeouts
:
FFFF timval equ -1
BAD8 exbios equ 0bad8h ; External BIOS call
; The next addresses are those addresses which
; must be changed after calling SID and the
; *.EMS file
6F72 timout equ 06f72h ; 1st patch address
6BA5 patch equ 06ba5h ; 2nd patch address
; The next value is the difference to real
; addresses after BIOS is installed
5200 differ equ 05200h
.z80
org timout
6F72' CD BDA5 call patch+differ ; Call new routine
org patch
6BA5 21 FFFF ld hl,timval ; Load timeout
6BA8' CD BAD8 loop: call exbios ; Test device ready
6BAB' 20 09 jr nz,fix ; Ok, exit to main
6BAD' 2B dec hl ; Else countdown
6BAE' 7C ld a,h
6BAF B5 or l
6BB0' 20 F6 jr nnz,loop ; All count down ?
6BB2' 21 FFFF ld hl,timval ; Yes, return to
6BB5' C9 ret ; count down again
6BB6' E3 fix: ex (sp),hl ; Fix caller's PC
6BB7' 23 inc hl ; To skip calling
6BB8' 23 inc hl ; 'EXBIOS'
6BB9' 23 inc hl ; At main level
6BBA' E3 ex (sp),hl
6BBB' C9 ret
end