🚀 go-pugleaf

>>>>> On 7 Oct 1992 22:08:24 -0500, ISB202REID@redgum.qut.edu.au (Did somebody say Coffee ??????) said:
Fodd> I was perusing Ralf Brown's interrupt list,
Fodd> when I found the entry for the real time AT clock on Int 70h.
Fodd> So I wrote a TSR that hooked it and hoped it would be invoked,
Fodd> every 1024th of a second.
Fodd> Absolutely nothing happened.
Fodd> Any Ideas ???

I looked into IBM's AT Technical Reference and found the following:
;--- HARDWARE INT  70H -- ( IRQ LEVEL  8 ) ------------------------------------
; ALARM INTERRUPT HANDLER (RTC)                                               ;
;       THIS ROUTINE HANDLES THE PERIODIC AND ALARM INTERRUPTS FROM THE CMOS  ;
;       TIMER.  INPUT FREQEUNCY IS 1.024 KHZ OR APPROXIMATELY 1024 INTERRUPTS ;
;       EVERY SECOND FOR THE PERIODIC INTERRUPT.  FOR THE ALARM FUNCTION,     ;
;       THE INTERRUPT WILL OCCUR AT THE DESIGNATED TIME.                      ;
;                                                                             ;
;       INTERRUPTS ARE ENABLED WHEN THE EVENT OR ALARM FUNCTION IS ACTIVATED. ;
;       FOR THE EVENT INTERRUPT, THE HANDLER WILL DECREMENT THE WAIT COUNTER  ;
;       AND WHEN IT EXPIRES WILL SET THE DESIGNATED LOCATION TO 80H.  FOR     ;
;       THE ALARM INTERRUPT, THE USER MUST PROVIDE A ROUTINE TO INTERCEPT     ;
;       THE CORRECT ADDRESS FROM THE VECTOR TABLE INVOKED BY INTERRUPT 4AH    ;
;       PRIOR TO SETTING THE REAL TIME CLOCK ALARM (INT 1AH, AH=06H).         ;
;------------------------------------------------------------------------------
As I can understand from code, INT 4Ah can be executed by it and its
handler can use registers AX,DX,DI,DS. Event wait uses cells 40:98..A0.
Alarm wait can be activated by INT 1Ah, CH=hour, CL=minute, DH=second,
AH=6 (sets CF if already active), reset (before alarm) by INT 1Ah, AH=7.
Event wait may be activated by INT 15h, AH=83h, AL=0, ES:BX=flag address,
CXDX=time (in us), (AH=83h, AL=1 clears event wait), also WAIT function
(INT 15h, AH=86h, CXDX=time) can use it. Seems there is a bug in BIOS
code: WAIT needs flag to be ORed with 80h and it is set to 80h, but
I'm looking in listing of very old BIOS, surely the bug is fixed now.