Beginnings of a virtual 6502 mode for Gigatron

Marcel of the Gigatron TTL Computer Project has announced a work-in-progress 6502 emulator, “v6502”, residing in ROM. (This complements the existing virtual machine: one is not expected to program the Gigatron at machine level, although it’s possible.)

Here’s Wozmon running on the virtual 6502:

From this thread on 6502.org and this thread on gigatron.io.

Oh, and there’s an in-browser emulator, of this not-at-all-an-apple-1:

Online emulator here: https://marcelk.net/gigatron/apple1/. Remember to type letters in UPPER case!

4 Likes

That’s a neat hack!
Fun stuff.

I decided to add the flashing @-cursor, map delete to rubout and all keys to uppercase. Much more authentic :slight_smile: . Interestingly, I could restore more of the original wozmon bytes along the way.

2 Likes

Hi All,

Marcel @marcelk has kindly shared a v4 ROM with me that contains the virtual 6502 code plus the 6502 WozMon and 6502 disassembler - as used on Apple 1.

I now need to take a crash-course in 6502 assembly language programming so that I can make full use of this whole new dimension to the Gigatron TTL Computer. :wink:

Also, this week, fellow Gigatron enthusiast xopr, has connected an Arduino to the Gigatron expansion pcb, using it as an SPI slave, which can be used as a general purpose GPIO peripheral processor. More details in this thread:

https://forum.gigatron.io/viewtopic.php?f=4&t=64&start=50

Upcoming Events:

If you are in the UK, I will be attending OSHcamp in Hebden Bridge on August 31st/ Sept 1st with a Gigatron presentation, and then with @marcelk at the Cambridge Centre for Computing History for their RetroComputer Festival on the 7th & 8th September.

OSHcamp https://wutheringbytes.com/

CCH http://www.computinghistory.org.uk/det/53612/Retro-Computer-Festival-2019-7th-8th-September/

regards

Ken

1 Like

@marcelk has posted an update over on the 6502 forum. With the best pi-related hack I’ve seen!

With 3583 bytes free it has the same free memory as the VIC-20. This is really a coincidence.

The main problem was to create sufficient continuous memory space. Although the Gigatron has 32K of RAM, 19KB of that is used for screen memory and the remainder is heavily fragmented. … the largest continuous block we have is just 512 bytes. BASIC itself needs 8KB…

Of course we then went overboard and added a flashing cursor, we made sure that the WAIT 6502 Easter Egg works, and that there is a π-symbol. The Gigatron doesn’t have that in its font, but it does have T and U… And… the font is stored without horizontal spacing, so there’s our glyph:

R         S         T   pi    U
v         v         v   v     v
x x x x . . x x x . x x # # # # . . . x
x . . . x x . . . . . . # . . # . . . x
x . . . x x . . . . . . # . . # . . . x
x x x x . . x x x . . . # . . # . . . x
x . x . . . . . . x . . # . . # . . . x
x . . x . . . . . x . . # . . # . . . x
x . . . x x x x x . . . # . . . # x x .
0 1 2 3 4 5 6 7 8 9 a b c d e f 1 1 1 1
^                               0 1 2 3
font82up

Good enough for me:

2 Likes