Hi All,
At present, the interface program for Logger just performs a slightly optimized
brute force search for the Logger device driver. Although reliable, it is very
slow compared to providing a simple interrupt call to test for installation.
Looking at the different interrupts, I think I have come up with a solution
that will work well for Logger and any other driver or program that needs such
a check. So, I’d like to propose a “standard” we could use. I’d like to get
your feedback on what I’m thinking…
Looking at RBIL, interrupt 0x2b is barely used by anything. Under MS-DOS and
FreeDOS, this simply points to an IRET. Under IBM ROM-DOS, AH functions
0x00-0x03 do some things. But, all other calls do nothing.
https://fd.lod.bz/rbil/interrup/dos_kernel/2b.html
<https://fd.lod.bz/rbil/interrup/dos_kernel/2b.html>
An install check issuing this interrupt would be simple to perform. A program
could set the Carry Flag, load AH/AX with “check for install” function and set
DS:BX to point to an identifier string (minimum 8 characters, no maximum). Then
call the interrupt. On return, if the Carry Flag is still set, then the install
check failed. If the Carry Flag is clear, it succeeded and other register would
be modified to according to the needs of the programs.
Implementation for Logger (as an example) could be:
CHECK:
push cs
pop ds ; set DS to our code segment
stc ; set the carry flag
mov ax, 0xfd00 ; set AX to install check function
mov bx, LOGGER_ID ; offset to LOGGER device driver ID
int 0x2b ; call install check interrupt
jc NOT_INSTALLED ; nothing changed, driver is not loaded
mov [DRIVER_PTR + 2], es ; save segment of far call to driver
function dispatcher
mov [DRIVER_PTR], di ; save offset of far call to driver
function dispatcher
jmp MAIN
DRIVER_PTR:
dw 0, 0 ; pointer to driver function dispatcher
LOGGER_ID:
db 'LOGGERxx' ; Logger device driver identifier. 8+
Characters.
MAIN: ; do program stuff
NOT_INSTALLED: ; driver not loaded, die now with error
message
As for the installed Driver, TSR or other extension, you just hook int 0x2b. If
AX=0xFD00 and DS:BX points to an identifier you recognize, then it would clear
the carry flag and return values in whatever registers required. Otherwise, it
completely ignore it and just jump to the previous interrupt handler.
It requires no additions to the kernel, is backwards compatible and should have
a low probability of any collisions.
Any thoughts on using it as a very minimal “standard” extension installation
check?
:-)
Jerome_______________________________________________
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