MB>From: Mervyn Baldwin 
MB>Subject: Re: Bosskey.Asm - sysreq.asm
MB>Hello Folks,
MB>New kid on block coming to you via e-mail.
MB>>It's not the same on the return. Which is major crash problem one. SS:SP
are
MB>>toasted after the INT 2E call.
MB>Need advice re INT 2eh. Have always heard it to be a dodgy INT, prone
MB>to cause worst sort of crashes. Is this true? Is it safe to use it
MB>instead of EXEC? Are there precautions which make it safer?
According to my reference ("PC Interrupts" by Ralf Brown & Jim Kyle), all
registers except for CS:IP get destroyed on return from an int 2Eh... however
you could do something like this:
******
.DATA
SaveSS  dw      ?
SaveSP  dw      ?
SaveBP  dw      ?
.CODE
SafeInt2Eh:
        MOV     [SaveSS], SS
        MOV     [SaveSP], SP
        MOV     [SaveBP], BP
        INT     2Eh
        CLI     ; make sure the restoration of the registers in uninterrupted
        MOV     AX, SEG _DATA
        MOV     DS, AX
        MOV     SP, [SaveSP]
        MOV     SS, [SaveSS]
        MOV     BP, [SaveBP]
        STI     ; registers restored, so interrupts OK
        RET
******
Normally you might PUSH registers to preserve them before an interrupt, but
since SS:SP is also destroyed, you have to take different precautions.
((Cloud))
MauveCloud@juno.com
 * OLX 2.2 * A dry sense of humor is better than slobbering everywhere
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