Re: [hatari-devel] Emulation of the TT second MFP

[Markus Fröschle <markus@xxxxxxx>]

Am Freitag, den 12.03.2021, 14:27 +0100 schrieb Nicolas Pomarède:

Le 12/03/2021 à 10:29, Markus Fröschle a écrit :

What kind of alarm does the ASV Unix code use ? Alarm after 'n' seconds 

or alarm on a specific date/time ? (maybe the required precision is less 

than 1 sec, I haven't check the nvram datasheet)

Neither. Hopefully I didn't make a mistake using Hatari's debugger, but this is what I found out so far:

*** skipping NVRAM reads done by TOS ***

Now we are in the ASV boot loader

Returning to emulation...

  $ffff8963 = $29

1. CPU breakpoint condition(s) matched 29 times.

( $ffff8963 ) . b ! ( $ffff8963 ) . b

CPU=$4fb74, VBL=2384, FrameCycles=47704, HBL=53, LineCycles=216, DSP=N/A

$0004fb74 : 13fc 000b ffff 8961                move.b    #$b,$ffff8961

> m b $ffff8961

FFFF8961: 0a 00 29 00 00 00 00 00 00 00 00 00 00 00 00 00   ..).............

Returning to emulation...

  $ffff8963 = $6

1. CPU breakpoint condition(s) matched 30 times.

( $ffff8963 ) . b ! ( $ffff8963 ) . b

CPU=$4fb82, VBL=2384, FrameCycles=47736, HBL=53, LineCycles=248, DSP=N/A

$0004fb82 : 0000 0040                          ori.b     #$40,d0

> m b $ffff8961

FFFF8961: 0b 00 06 00 00 00 00 00 00 00 00 00 00 00 00 00   ................

Returning to emulation...

WARN : Write to unimplemented RTC/NVRAM interrupt enable bits 0x40

  $ffff8963 = $46

1. CPU breakpoint condition(s) matched 31 times.

( $ffff8963 ) . b ! ( $ffff8963 ) . b

CPU=$4fb94, VBL=2384, FrameCycles=47784, HBL=53, LineCycles=296, DSP=N/A

$0004fb94 : 4cee 003c fff0                     movem.l   $fff0(a6),d2-d5

> m b $ffff8961

FFFF8961: 0b 00 46 00 00 00 00 00 00 00 00 00 00 00 00 00   ..F.............

According to my MC146818A documentation, the following appears to be done by ASV:

RTC register $a = $29  # = %00101001

RTC register $b = $06  # = %00000110

RTC register $b = $46  # = %01000110

Register $a: $29: clock = 32.768 kHz clock rate, rate select 1001 <> 8 x 1 + 4 x 0 + 2 x 0 + 1 = 9, resulting in a frequency of 32768 Hz / 2^8 = 128 Hz.

Register $b: PIE (periodic interrupt enable) on, BCD off, 24hrs on, Daylight saving off

The periodic (free running) interrupt is supposed to trigger with 128 Hz.

The VBL doesn't seem to be granular enough, I reckon.