gw@sickkids.UUCP (CFI/Graham Wilson ) (09/01/87)
I am writing an interrupt handler and have run into a snag with MASM. The solution may be obvious, but I can't seem to figure it out. The situation is as follows. The clock tick (IRQ0) has been speeded up by a factor of 32, and IRQ0 (INT 8) jumps to my routine. Every 32 interrupts, control passes to the BIOS INT 8 handler when my routine is done. The problem is that I can't figure out how to pass control to the BIOS routine. I tried saving the offset and segment values from the interrupt table before changing to my address. These values are saved as *CODE SEGMENT* variables jmpoff and jmpseg respectively (in that order). If control is to pass through to BIOS, I execute the command: jmp FAR [cs:jmpoff] Which I had assumed would work. The first two bytes of the opcode generated by MASM are 0xff and 0x26. To the best of my knowledge, they should be 0xff and 0x3e. Does anyone know how to correctly set up the jump? Any help is greatly appreciated. Thanks bunches in advance. Graham Wilson | ...allegra ...decvax CyberFluor Inc | \ \ 179 John St., Suite 400 | ...linus!utcrsi!utzoo!sickkids!cfi!graham Toronto, Ontario, M5T 4B1 | / / (416) 977-5450 | ...watmath ...ihnp4
yingda@vms.macc.wisc.edu (Ying-Da Lee) (09/03/87)
In article <69@sickkids.UUCP> gw@sickkids.UUCP (CFI/Graham Wilson (977-5450) [RI7921Z]) writes: >I am writing an interrupt handler and have run into a snag with MASM. >The solution may be obvious, but I can't seem to figure it out. > >The situation is as follows. The clock tick (IRQ0) has been speeded up >by a factor of 32, and IRQ0 (INT 8) jumps to my routine. Every 32 interrupts, >control passes to the BIOS INT 8 handler when my routine is done. The >problem is that I can't figure out how to pass control to the BIOS routine. > >I tried saving the offset and segment values from the interrupt table >before changing to my address. These values are saved as *CODE SEGMENT* >variables jmpoff and jmpseg respectively (in that order). If control >is to pass through to BIOS, I execute the command: > > jmp FAR [cs:jmpoff] > What you need is jmp dword ptr cs:jmpoff Alternatively, you could define an additional label, e.g., old_int8 equ dword ptr $ jmpoff dw ? jmpseg dw ? then a simple jmp cs:old_int8 will do.