Search found 43 matches

by Sugarplum
25 Nov 2021, 23:52
Forum: Support
Topic: Nonfunctional Gigatron.
Replies: 13
Views: 306

Re: Nonfunctional Gigatron.

Hmm. The first couple of tests look close to how I'd expect. One that would be interesting to know would be to look at the low bit of the lowest nybble of the program counter output (pin 14 of the '161 I think), not its clock, but the data. A counter chip, if allowed, will increment. The fastest cha...
by Sugarplum
25 Nov 2021, 12:27
Forum: Support
Topic: Nonfunctional Gigatron.
Replies: 13
Views: 306

Re: Nonfunctional Gigatron.

I found out you can use an arduino and make a simple oscilloscope with processing IDE and I tried it with my signal generator and it seems to be pretty accurate, out of curiosity what should the waveform look like? Should it be a square wave, a sine wave? My common sense and good bit of electrical ...
by Sugarplum
24 Nov 2021, 03:27
Forum: Support
Topic: Nonfunctional Gigatron.
Replies: 13
Views: 306

Re: Nonfunctional Gigatron.

If you have a scope, one of the first things I'd check is the clock output. Another thing to check would be the power supply, maybe try another one with a higher mA rating.
by Sugarplum
23 Nov 2021, 08:38
Forum: Hardware and software hacking
Topic: Can I build with HC rather than HCT series ICs ?
Replies: 5
Views: 232

Re: Can I build with HC rather than HCT series ICs ?

Yeah, the oscillator is about the only thing that is particularly picky. Most other inverter chips for that either won't oscillate (at least not in that configuration) or don't exist. When you go toward smaller packages, you find fewer available chips. Someone else noticed better stability with HCT ...
by Sugarplum
12 Nov 2021, 00:46
Forum: Hardware and software hacking
Topic: 10MHz, 12.5MHz and Beyond!
Replies: 42
Views: 24147

Re: 10MHz, 12.5MHz and Beyond!

The more I think of it, a 4-stage Gigatron compatible CPU could allow for a theoretical maximum of 100-120 Mhz. Looking at the instructions, the only write operations on RAM are simple stores. The reads can have ALU operations done on them. So stage 1 would be Fetch, 2 would be Decode, 3 would be fo...
by Sugarplum
04 Nov 2021, 10:47
Forum: Hardware and software hacking
Topic: Implementing a faster multiplication routine
Replies: 20
Views: 3369

Re: Implementing a faster multiplication routine

Speaking of the "weird instruction," [if (A != 0) PC = hi(PC)|A], that is $hEE. I found that on this site: https://www.iwriteiam.nl/PGigatron.html
by Sugarplum
31 Oct 2021, 14:17
Forum: Hardware and software hacking
Topic: 10MHz, 12.5MHz and Beyond!
Replies: 42
Views: 24147

Re: 10MHz, 12.5MHz and Beyond!

While I don't see 100-125 Mhz as practical on a hardwired Gigatron, I think I know how to get it a little closer. If you have a shadowed LUT control unit, you could try to simplify the AND/OR of an immediate done to RAM and sent to OUT. A 2-bit mini "ALU" might be an option. To create sync...
by Sugarplum
29 Oct 2021, 03:57
Forum: Hardware and software hacking
Topic: 10MHz, 12.5MHz and Beyond!
Replies: 42
Views: 24147

Re: 10MHz, 12.5MHz and Beyond!

It is probably impossible to split vCPU instructions into 7 cycle subunits. Maybe one could use a FIFO chip (as in the Video Repeater). The Gigatron would fill the FIFO at the beginning of each scanline, and the FIFO would deliver the pixels on time for the VGA screen. That way, all the inter-pixel...
by Sugarplum
28 Oct 2021, 07:52
Forum: Hardware and software hacking
Topic: 10MHz, 12.5MHz and Beyond!
Replies: 42
Views: 24147

Re: 10MHz, 12.5MHz and Beyond!

On further thought, I think I can see how 120 Mhz might be possible. That would require going to a purer RISC model and being more accumulator-centric. Since the best ALU+RAM latency is probably about 15ns, then if you only use the ALU or the SRAM, you can get that down to 8 ns. But that would compl...
by Sugarplum
26 Oct 2021, 11:41
Forum: Hardware and software hacking
Topic: 10MHz, 12.5MHz and Beyond!
Replies: 42
Views: 24147

Re: 10MHz, 12.5MHz and Beyond!

I think I know how to get a discrete chip Gigatron up to 50 Mhz. Do it using SMD, do a LUT-based control unit shadowed into 8 ns SRAM, shadow the instruction ROM too, use 3 pipeline stages, use Drass' 6.7 ns ALU, and use 8ns system SRAM. Unless the SRAM can be uncoupled, about 66.667 Mhz would be th...