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mac_via: fix rtc command decoding for the PRAM seconds registers 

Analysis of the MacOS toolbox ROM code shows that on startup it attempts 2
separate reads of the seconds registers with commands 0x9d...0x91 followed by
0x8d..0x81 without resetting the command to its initial value. The PRAM seconds
value is only accepted when the values of the 2 separate reads match.

From this we conclude that bit 4 of the rtc command is not decoded or we don't
care about its value when reading the PRAM seconds registers. Implement this
decoding change so that both reads return successfully which allows the MacOS
toolbox ROM to correctly set the date/time.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20230621085353.113233-25-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
This commit is contained in:
Mark Cave-Ayland 2023-06-21 09:53:53 +01:00 committed by Laurent Vivier
parent ce47d531c3
commit 532009054b
1 changed files with 6 additions and 5 deletions
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11
hw/misc/mac_via.c
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@ -362,10 +362,10 @@ static void pram_update(MOS6522Q800VIA1State *v1s)
*
* Command byte Register addressed by the command
*
* z0000001 Seconds register 0 (lowest-order byte)
* z0000101 Seconds register 1
* z0001001 Seconds register 2
* z0001101 Seconds register 3 (highest-order byte)
* z00x0001 Seconds register 0 (lowest-order byte)
* z00x0101 Seconds register 1
* z00x1001 Seconds register 2
* z00x1101 Seconds register 3 (highest-order byte)
* 00110001 Test register (write-only)
* 00110101 Write-Protect Register (write-only)
* z010aa01 RAM address 100aa ($10-$13) (first 20 bytes only)
@ -373,6 +373,7 @@ static void pram_update(MOS6522Q800VIA1State *v1s)
* z0111aaa Extended memory designator and sector number
*
* For a read request, z=1, for a write z=0
* The letter x indicates don't care
* The letter a indicates bits whose value depend on what parameter
* RAM byte you want to address
*/
@ -389,7 +390,7 @@ static int via1_rtc_compact_cmd(uint8_t value)
}
if ((value & 0x03) == 0x01) {
value >>= 2;
if ((value & 0x1c) == 0) {
if ((value & 0x18) == 0) {
/* seconds registers */
return read | (REG_0 + (value & 0x03));
} else if ((value == 0x0c) && !read) {