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So assuming one wanted to buy a used one of these (I had timex sinclairs around this time) how would one display the composite video nowdays?
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It's cool because the registers are all in RAM, with a "workspace pointer" on the CPU pointing at where they are. This is slow, but a context switch is just changing that pointer.
Yep, but it lacks a MMU so memory protection and paging are going to require a lot of work. I think the only reason this is feasible at all is they're running the OS out of a ROM cartridge.
I thought UsagiElectric showed a case where his Centurion didn’t, but I may be misremembering.
HOLY COW. Thank you for this. I LOVE the Ti99/4a, its one of the first computers I ever used. I've got one up and running at home now currently and can't wait to try this.
Earlier quoted context omitted.
It's cool because the registers are all in RAM, with a "workspace pointer" on the CPU pointing at where they are. This is slow, but a context switch is just changing that pointer.
Yep, but it lacks a MMU so memory protection and paging are going to require a lot of work. I think the only reason this is feasible at all is they're running the OS out of a ROM cartridge.
I'm pretty sure the Centurion doesn't run Unix.
Earlier quoted context omitted.
Same here - parents bought one for me in 1982, IIRC. By 1984 I had moved to Atari XL, but I'll always have a soft spot for the TI-99/4A, Extended Basic cartridge, speech synthesizer, cassette drive, etc. My sister and I used to co-type programs from "Compute!". The times were so much simpler then..
The TI99/4A was my first computer when I was 7 or 8. Unfortunately, no cassette drive. As soon as I shut it off, my basic program was gone!
HOLY COW. Thank you for this. I LOVE the Ti99/4a, its one of the first computers I ever used. I've got one up and running at home now currently and can't wait to try this.
@UsagiElectric on YouTube has a series of videos on building a homebrew around the TMS9900 processor. Would be cool if a unix-like OS could be used on something like that, though sounds like this project is specifically targeting the TI-99/4A system. The TI-99/4A was the first computer I owned as a teenager. I had used TRS-80s and Apple ][ at school. I eventually bought the expansion box and a couple of accessory car…
@UsagiElectric on YouTube has a series of videos on building a homebrew around the TMS9900 processor. Would be cool if a unix-like OS could be used on something like that, though sounds like this project is specifically targeting the TI-99/4A system. The TI-99/4A was the first computer I owned as a teenager. I had used TRS-80s and Apple ][ at school. I eventually bought the expansion box and a couple of accessory car…
Can you drop this yt channel name?
Earlier quoted context omitted.
While the CPU is a better fit than the 8 bit contemporaries, the 16kb of working memory is going to be a struggle.
It's cool because the registers are all in RAM, with a "workspace pointer" on the CPU pointing at where they are. This is slow, but a context switch is just changing that pointer.
It's arguably the only 8-bit computer which has a really different architecture from the others. You could otherwise imagine pulling the SID chip off a C-64 and putting it on a TRS-80 Color Computer etc.
Sharing the main RAM with video was a weak point in computers of that time period because the video system stole many of the memory access cycles. Some recent retrocomputers that revisit that period like
https://www.c64-wiki.com/wiki/Commander_X16
have a full-size memory bank and a video RAM memory bank which is accessed through a port which can be pretty efficient because you can auto-incremement the address register and just write 1 byte to the port to write 1 byte to video RAM and repeat.
HOLY COW. Thank you for this. I LOVE the Ti99/4a, its one of the first computers I ever used. I've got one up and running at home now currently and can't wait to try this.
Btw, there is a lovely third party replacement for the TI99/4a video chip that lets you output VGA. It’s a major life improvement if you are seriously using it. I Dremeled my case but you can route the ribbon cable to avoid it if you’d prefer not to modify anything. Happy to send you a link if you don’t already know about it.