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Context switching and message passing (synchronous anyway) are the same thing when you consider how rendezvous works.
BLWP instructions seem like this was “meant to be”.
Wow. The TI-99 is such a perfect fit for this too given the chip was designed for multi-user computing in a way other home computer chips weren’t. All due to TI’s desire to use the same chip standards across all their machines big and small, IIRC.
While the CPU is a better fit than the 8 bit contemporaries, the 16kb of working memory is going to be a struggle.
UNIX99 uses an after market card with 1Mbyte of RAM on an 8bit external buss used for peripherals. This card replaces the old 32K RAM card made by TI in the 1980s.
I wonder if this kind of architecture would be fun to build an L4 microkernel based system with. Context switching and message passing (synchronous anyway) are the same thing when you consider how rendezvous works. BLWP instructions seem like this was “meant to be”.
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Thanks! I've got mine running in to a 9" Pelco PVM and it works well but yea, its tiny. I'd love to plumb in VGA and use a 15" flat panel. Would love a link.
https://www.tindie.com/products/visrealm/pico9918/ There is very little documentation with this device but fortunately several YouTubers have made long videos showing every detail of the replacement. Enjoy!
I wish there were some cheap FPGA version of the 3rd party implementation of the planned successor, the TI-99/8. It was called the Geneve 9640 from Myarc: https://dressupgeekout.com/geneve/ http://www.mainbyte.com/ti99/geneve/geneve.html Wikipedia has a decent article: https://en.wikipedia.org/wiki/Geneve_9640 12 MHz un-crippled 16-bit CPU, 80 column text, 256 colour graphics, up to 2 MB of RAM. That would be much mo…
Both are available in MESS.
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Was that part of some kind of cost optimization? Why would anyone design such an obscurity?
The whole thing seems like it was designed in a parallel universe, or at least it reeks of some kind of a sunk-cost-fallacy design-by-committee thing. Supposedly what happened is that the system was originally designed to have either an 8-bit CPU, or a 16-bit CPU with an 8-bit bus (cf. 8086/8088) like TI's own TMS9985, but at some point it was decided that they should instead cram their full 16-bit TMS9900 minicomput…
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From 1977 they expected a 9985 to succceed the cheap 40-pin 9981, both having an 8-bit external bus (1). It would have 256 bytes of RAM onboard. I speculate it would have the 9900 microcode optimizations seen in the military SBP9989.
Anecdotally, the 9985 failed seven tape-outs. It was killed. The Bedford UK team was tasked with starting over: eventually this produced the 9995.
But the Home Computer had been prototyped using a 9900 board. So that was forced into the 99/4 (not A) with some external 256 byte SRAM.
Memory was expensive. The 9918 VDP, made by a team in 1975 with junior engineer Karl Guttag, was the cheapest way to interface 4Ks DRAM which TI made and sold to itself. By the time it reached market, 16k in 8x 4116s was optimal.
Various efforts to cost-reduce and upgrade the 99/4A ran into the '82 price-war with Commodore.
Every design iteration that added more RAM (2 or 8 or 16K directly accessible from the CPU) was "paid for" by reducing the cost elsewhere (PALs for instance.) BOM was around $105. [3]
But in the price war, engineers were told to deploy the cost-savings without any new features: this was the 99/4A 2.2 or QI for quality improved. [3] The 99/4A was already a loss leader by Q4 1982 [5].
In 1981, Karl Guttag's new 9995 passed first silicon [2]. It used the new optimized 99000 CPU core which also famously passed on first tape-out. The 9995 was available in quantity in 1982 [3] when new consoles were started around it: 99/2, 99/8.
The 99/2 was supposed to be cheap enough to compete with Sinclair. [6]
The 99/8 was a technical beast for the high-end, having 64K of directly accessible RAM. Its fancy memory mapper drove 24 bit external addresses. It supported 512K off board, which the P-Box had been designed for. It had Pascal built-in. Yet there was no Advanced VDP for it: stuck with the same 9918A.
In early 1983, TI assembled a team of two dozen engineers to write software for it: Pascal applications, new LOGO, a database, new word processor, TI FORTH, and complete accounting package, and a rumored superior easy-to-use interface. Pascal was supposed to deliver many benefits. It would be a small business machine. (4)
Of course, in November 1983, all efforts ceased as Home Computer was cancelled--just as the consoles were to be unveiled at Winter CES.
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(1) An 8-bit bus was always going to be optimal--even the IBM PC 8088 saw that. 16-bit peripheral chips were never going to be made: the package size would prohibit that.
(2) Electronics Magazine and EE Times articles
(3) Internal memos of Don Bynum, program manager
(4) TI Records, DeGolyer Library, SMU : Armadillo and Pegasus
(5) "Death of a Computer", Texas Monthly, end of 1983?
(6) BYTE Magazine June 1982-ish
Based on research for my book: _Legacy: the TI Home Computer_.
From memory...
What features does one specifically mean by "UNIX-like"? Unified filesystem with a single root? A CLI shell with the classic abbreviated comands? Preemptive multitasking? Multiuser-oriented permissions?
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Well I mean it fits in with the 8-bit era machines as far as performance but that CPU was absolutely 16 bit.
16-bit registers, operations, etc. yeah. A bigger machine of the TM9 series would be more like a PDP-11.
The 990 series of minicomputers were competing with PDP-11s (Though DEC had highest market share, I believe 33% of the whole mini market?)
The 9900 was condensed in 1975 and went into the low-end 990/4. The higher end 990/9 and 990/10 were always going to be discrete TTL as the 9900 didn't support memory protection or mapping to the 2MByte total address space.
TI was always conscious of not challenging IBM head-to-head in minicomputers. Internal memos always projected TI's plan for its minis to occupy a space well below the latest IBM mainframes. From 1980, the planned 990/12 would arrive just as IBM delivered more compute power in their low-end... this was intentional, supposedly because IBM was the chief driver of TI's transistor business!
Earlier quoted context omitted.
The whole thing seems like it was designed in a parallel universe, or at least it reeks of some kind of a sunk-cost-fallacy design-by-committee thing. Supposedly what happened is that the system was originally designed to have either an 8-bit CPU, or a 16-bit CPU with an 8-bit bus (cf. 8086/8088) like TI's own TMS9985, but at some point it was decided that they should instead cram their full 16-bit TMS9900 minicomput…
The design "decisions" are easy to explain. The 9985 failed. They had a development prototype with a 9900 emulating the expected CPU. The 9918 VDP was the cheapest way to add 4K later 16K of DRAM. And that was what they shipped after the 9985 was killed. ------------------------------ From 1977 they expected a 9985 to succceed the cheap 40-pin 9981, both having an 8-bit external bus (1). It would have 256 bytes of RA…
Do you think there is a possible world where TI would have swallowed their pride and considered not-invented-here options like a regular 8080/Z80/6502 as the CPU?
Earlier quoted context omitted.
The design "decisions" are easy to explain. The 9985 failed. They had a development prototype with a 9900 emulating the expected CPU. The 9918 VDP was the cheapest way to add 4K later 16K of DRAM. And that was what they shipped after the 9985 was killed. ------------------------------ From 1977 they expected a 9985 to succceed the cheap 40-pin 9981, both having an 8-bit external bus (1). It would have 256 bytes of RA…
Thank you for this, this is very interesting detailed context. Do you think there is a possible world where TI would have swallowed their pride and considered not-invented-here options like a regular 8080/Z80/6502 as the CPU?
There was a memo asking if TI should support those other CPUs in their AMPL prototyping system (990 based tools and in-circuit emulator). That investment was rejected.
Anecdotally, Don Bynum was unhappy with slow progress on defining the Home Computer, and hacked together a Z80 based machine. The engineers redoubled their efforts... supposedly...
There's politics between the Calculator division (all consumer products), Semiconductor, and Data Systems Group.
Still, TI had a TMS8080 (and later their own 486).
I'll work on this idea, thanks...
---- As a child, I knocked some books off a garage shelf once and was plonked on the head with copies of The 8080 Bugbook. What the heck was a Bugbook? Or an 8080?
Some years later, a 9995 data sheet fell on my head and I thought how hard can it be to wire up a computer?