As noted in a thread elsewhere, when TI failed to capitalise on their 9900 CPU in their TI-99/4(a) computers, a company called Myarc which had made addons for those designed and eventually sold their own bigger, better, compatible machine, the Geneve:
The goal of the Graphics Programming Language was to isolate the programmers from the complexity of using the various memories in the machine. The 128 words of RAM and built-in system and GPL ROMs were simple enough, but the 16KB of video memory required writing the address to a 9918 register in two halves and the reading or writing the actual byte from another register. Accessing the Basic and cartridge ROMs was just as complicated.
Tiny Basic was implemented as an interpreter written in an imaginary language (IL) which in turn was implemented as an interpreter in machine language. So TI did the same for its Basic and used the opportunity to make all those odd memories look normal not only for Basic itself but for any cartridges.
But the most options were offered by Compupro, with S100 boards including the hybrid 8085/8088, the 8086/8087, the 286, the 186, the 68000 and the 32016.
GPL strikes me almost like a wonderland version of Sweet16: it provides access to byte-oriented memory and runs on a word-oriented 16 bit MPU. (And yes, I see there are three memory spaces as seen by GPL: CPU memory, Video memory, and G memory.) Here’s some documentation: http://www.unige.ch/medecine/nouspikel/ti99/gpl.htm
(Of course, the above is about TI’s GPL, not Tomy’s.)
For those who like that kind of thing, there’s a go-faster FPGA implementation of the 9900 here:
Free yourself from the one byte world. Move up to the two byte Texas Instruments TMS-9900 16-bit microprocessor — with our — “super starter system” — TEC-9900-SS. Shown above, features hardware multiply and divide, 69 mini-computer instructions, 7 addressing modes, expandable to a full 65k bytes; Monitor, TMS 9900 cpu, ram, p-rom, e-prom, programmer all on one P-C Board basic operating system as low as $299 unassembled $399 assembled and tested.
That Myarc 9640 was an impressive feat of engineering, I thought! That someone could duplicate the functionality of the TI-99/4a, which was so proprietary, really amazed me. And a blazing fast 12 Mhz!! I still like TMS 99xx assembly-language far more than 80x86.