High score cart source code

[DEBRO]

Hi there,

 

This question isn't related to the source code but more around detecting the presence of the HSC.

 

Do we know of anything else that potentially loads up in location $3900? What are the values of these locations when the HSC isn't present? Is it safe to check for the HSC as...

   lda #$38
   eor $3900                        ; a should be 0xFE if HSC present
   eor $3904                        ; a should be 0 if HSC present
   bne NOHSC

 

[RevEng]

There's nothing else that presently uses the $1000 and $3000 HSC locations, AFAIK. If there's no HSC, the bus is floating/undefined at $3900, so any reads will typically echo back the last value on the bus. (ie. the last byte of the opcode) I say typically - the values returned may be corrupted or just FF, with oddball consoles.

 

The other thing you can do is look for the HSC magic signature at $1002. Heads up the bus is floating there too, if HSC isn't plugged in. 7800basic just checks for the first 2 bytes of that signature, which IMO is enough.

 

I think looking at the ROM contents might be problematic, in case there's ever a revision. (not likely, but not impossible)

[DEBRO]

Hi there,

4 hours ago, RevEng said:

The other thing you can do is look for the HSC magic signature at $1002. Heads up the bus is floating there too, if HSC isn't plugged in. 7800basic just checks for the first 2 bytes of that signature, which IMO is enough.

I may not be understanding. Is the "magic signature" unique for each HSC? What is the advantage of checking the signature vs. the $3900 and $3904 locations as GCC implemented? 

[RevEng]

Ok, my bad. I had a look at the disassembly just now and see that $3900 and $3904 are set aside as an HSC rom magic, so those won't change. (the magic at $1002 indicates the presence of formatted HSC write area, and isn't unique.)

 

In my defense I don't use the HSC rom routines, because 7800basic supports high score table saving to both the HSC and Savekey/Atarivox with common routines.

[+Mitch]

Is the alt version of the High Score ROM that I posted a few years ago much different than the standard ROM. Not that I am aware of anyone actually using it.

 

Mitch

[RevEng]

I can't find that alternate HSC ROM offhand, and must have missed it the first time around. Do you have a link, or can you attach it here?

[+Mitch]

highscore.Bin I believe it is this one.

 

Mitch

[RevEng]

Doing a quick manual disassembly on the first few bytes, it looks like that alternate hsc rom has corruption, rather than meaningful code differences.

 

Right near the start I see a 3 byte JSR being changed into a 2 byte LDA # instruction, leaving that 2nd byte of the JSR as the load, and 3rd byte just waiting to being executed. This change occurs right after another LDA, so it's pointless and problematic. A little further on I see a 1 byte opcode being replaced with the first byte of a 2 byte opcode, messing up the alignment of the code that follows.

 

The code alignment doesn't seem to shift either, like I'd expect in a code revision.

[+Mitch]

Thanks for checking. There was not a cover on the Eprom so I guess it may have started to erase.

 

Mitch

[gambler172]

On 1/24/2020 at 9:22 PM, Mitch said:

Thanks for checking. There was not a cover on the Eprom so I guess it may have started to erase.

 

Mitch

is there a 3600 Asteroids somewhere available?

[+Mitch]

2 hours ago, gambler172 said:

is there a 3600 Asteroids somewhere available?

Do you mean a proto that actually says 3600 on it? I am not sure if they started work on it before the name change to 7800. Maybe Curt has one.

I do have one called 3d Asteroids,  the same as what the catalog shows. It is the same game as regular 7800 Asteroids.

 

Mitch