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Contents of GROM >00E8?


senior_falcon

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I would like to know if the contents of GROM at >00E8 are the same in the three versions of the TI-99/4A. In Classic 99 you can see that >00E8 contains >0FFF in both the TI-99/4A console and the TI-99/4A V2.2 console. But I understand there were two different versions of the standard console. Can someone verify that both versions contain >0FFF at this grom address? Thanks!

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I guess the Intern stumbled upon differences !?

 


********************************************************************************
*
* CONSOLE GROM 0 ANALYSIS TI99/4A
*
* 9.6.84 H. Martin
*
********************************************************************************

004C : DATA >B0 Here change in some GROMS: Set pointers to the
004D : DATA >B0 character blocks. The other routines are shifted
004E : DATA >70 3 bytes upwards.
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There seem to be at least three different GROM sets... two versions prior to 2.2 and the 2.2 set itself. TI Intern does seem to document the differences. I can't confirm that I have both sets of GROMs, but on my machines (2.2 and pre-2.2) >00E8 does have >0FFF

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I guess I could have been more specific in my question. This is not just idle curiosity. I have written a GPLLNK routine for the playground environment, which means that everything has to run out of the scratchpad. The memory location I asked about lets me do an XML and return to the scratchpad and to the calling program. On playground, option 1, (TI-99/4A) and option 3 (V2.2) work fine. I would like to verify that a console that requires you to press option 2, (TI-99/4A (alt)) will work with this GPLLNK routine. If it has >0FFF at grom >00E8 then it will work. I have a feeling that because it is the same in V2.2 and the usual TI-99 that it will also be the same in the alt version, but would like to know for sure. So if someone who has a console that needs option 2 in playground would be able to test this I would appreciate it. If you have such a console but can't look into the grom I can send a program that uses gpllnk and that would be a good test.. Thanks!

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Hmmm. The >0FFF is part of the routine that initializes the first 4k of VDP Ram. This was one of the early patches discovered for the EA cart from the disassembly of Grom 0 because EA cart it didn't clear enough VDP memory in one of the loaders (option 5 ?) if it was used several times in succession to load different programs. Sometimes the loader would fail if there was garbage left in VDP memory and replacing the lesser value with >0FFF solved the problem. Does your application reference this in some manner? ;)

 

Gazoo

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Sometimes I can be a bit obtuse - it turns out I had that information all the time. Iin my copy of Intern I have written directly under "CONSOLE GROM 0 ANALYSIS" the words "Black & Silver Grom is different" and lower on the page in the text: "Here change in some GROMS.....routines are shifted 3 bytes upwards." Sure enough, >00E8 in INTERN is different from the 2 groms in Classic99. Bummer. But it turns out that one (and only one!) other address will work for me. At >1675 is the value >0FFE and that is the same in the 3 groms. (It is part of the text for the cassette loading routines.) I just need to adjust the code a wee bit...

 

To answer Gazoo's question, I need two bytes in a row: >0F (XML) and >Fx. The first F sets the base address at >8300. Add 2 x the second nybble to get the address. This works out to >831E for >0FFF or >831C for >0FFE. The GPL XML code is at rom >0608. This GPLLNK subroutine is adapted from miller's graphics universal gpllnk and dsrlnk and after much head scratching I was able to figure out how this worked to be able to point the return to the scratchpad instead of the 32K memory expansion.

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