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Re: Running MS-DOS with a custom built PC-BIOS on an S-100 system

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"monahanz" <monahan@vitasoft.org> wrote in message
news:df366a16-872d-43e1-b4d0-9e5585ebe2c8@a10g2000prn.googlegroups.com...
>
> What has me puzzeled however with V3.3 (Not 3.0 or earlier) is that at
> the A> prompt there is a continuous stream of Int 15h with AH=41H
> being sent.   I looked it up this is what I could find:-
>
> [RBIL description]
>
> I can find little on the web to explain what this INT is doing. Does
> anybody know. How can I satisfy it and make it go away.
>

From the input parameters, you should be able to determine which memory
location (ES:DI) or port (DX) that it's waiting on (decided by AL bit 4) and
what byte value or bit combination that it's looking for or for a change in
(mask or comparison in BH).  Hopefully that'll answer the question.  The I/O
port addresses are known, and memory locations, like the BIOS data area, are
also.

FYI, AIUI, this is what the RBIL description means.  It waits for a value to
change, or can time out if the value doesn't change or wait forever.  It
waits on a byte whose address is in ES:DI, if AL bit 4 is clear(0).  Or, it
waits on byte at port value of DX, if AL bit 4 is set(1).  It'll timeout
waiting for a change after BL*55ms, or loop indefinately if BL is zero.
Also, it uses the value in BH as a mask or compare value with that byte
value to test for a change (set by AL bits).  The test (AL bits) is for
various selectable conditions (Table 00463).  Bit 1 or 2 set for AL uses BH
as a comparison (probably x86 CMP instruction) and returns for equal or not
equal.  Bit 3 or 4 set for AL uses BH for a test (probably x86 TEST
instruction) and returns for zero or not zero.  The question is what is Bit
0 "any external event".  An interrupt?  An NMI?

HTH,


Rod Pemberton

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Running MS-DOS with a custom built PC-BIOS on an S-100 system monahanz <monahan@vitasoft.org> - 2011-08-23 22:27 -0700
  Re: Running MS-DOS with a custom built PC-BIOS on an S-100 system "Rod Pemberton" <do_not_have@noavailemail.cmm> - 2011-08-24 14:23 -0400
    Re: Running MS-DOS with a custom built PC-BIOS on an S-100 system monahanz <monahan@vitasoft.org> - 2011-08-25 00:33 -0700

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