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I decided to build a nine-bit computer

madned.substack.com

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Re: I decided to build a nine-bit computer

#11

Post by IshKebab »

sillyquiet wrote: post #6

Regarding the interesting bit (to me) in there about the advantages of FPGAs over an SBC like the Pi (speed)- does anybody know of any blogs or projects where an FPGA's speed helped in a hobby project where software running on an SBC wasn't fast enough? I can imagine a few, mostly real-time projects involving expensive computations (image or pattern recognition maybe?), but I would love to see some concrete examples.

I think you won't find many because an FPGA that is as fast at computation as a Raspberry Pi will be thousands of pounds. The real advantage is latency and low-level control.

Re: I decided to build a nine-bit computer

#12

Post by sillyquiet »

FredFS456 wrote: post #9
sillyquiet wrote: post #6

Regarding the interesting bit (to me) in there about the advantages of FPGAs over an SBC like the Pi (speed)- does anybody know of any blogs or projects where an FPGA's speed helped in a hobby project where software running on an SBC wasn't fast enough? I can imagine a few, mostly real-time projects involving expensive computations (image or pattern recognition maybe?), but I would love to see some concrete examples.

RF/radio is one solid application. Can't really do the signal processing fast enough on an SBC.

Ohh good one. mmRadar projects I guess will fall into this category too.

Re: I decided to build a nine-bit computer

#14

Post by buescher »

googamooga wrote: post #7

Ternary logic based computer Setun with 9-bit "bytes" was developed in late fifties in the USSR. Not much info on about it in English, unfortunately. https://en.wikipedia.org/wiki/Setun

Ternary on binary systems usually uses a 2-bit "trit" with an extra potential state. That's even how the later Setun machines did it, from what I understand. Oh yes, and the Soviets even developed their own trinary Forth dialect for them.

Re: I decided to build a nine-bit computer

#15

Post by amelius »

enriquto wrote: post #8
mad_ned wrote: post #5

Earlier quoted context omitted.

haha yes, excellent suggestions! I did think about ternary logic actually but I don't know of an FPGA that supports it. I considered creating like a primitive that burns 2 register bits to approximate it even, and just throw away the 4th state and pretend I have 3-state logic on all the layers above. but i have enough on my hands just trying to get the stupid timing working on a simple CPU. Im not actually a CPU desi…

Throwing away 25% of your bits sound wasteful... what you need is a moderately large power of 2 that is very close to a power of 3. These can be found by computing the continued fraction of log(3)/log(2). The sequence of convergents starts thus 2/1, 3/2, 5/3, 8/5, 11/7, 19/12, 46/29, 65/41, 84/53. Some good choices seem to be 2^8-3^5=13 (loses 5%) or 2^46≈3^29 (loses 2.5%).

You can also detect Z state by driving the input high, reading, then driving the input low, reading. If both reads are different, then you have a Z state. Otherwise, the input is the read state.

Of course, drive the input through a resistor.

Re: I decided to build a nine-bit computer

#16

Post by PragmaticPulp »

sillyquiet wrote: post #6

Regarding the interesting bit (to me) in there about the advantages of FPGAs over an SBC like the Pi (speed)- does anybody know of any blogs or projects where an FPGA's speed helped in a hobby project where software running on an SBC wasn't fast enough? I can imagine a few, mostly real-time projects involving expensive computations (image or pattern recognition maybe?), but I would love to see some concrete examples.

Basically anything with significant real-time requirements or high bandwidth requires an external FPGA or microcontroller.

Embedded Linux is great, but if you’re trying to do something like read from a high-speed ADC then the only way to do it is with an FPGA. The FPGA reads from the ADC at precise intervals and buffers the data. The embedded Linux system can then periodically read the buffer with all of the jitter and latencies that come with using Linux.

Virtually every Linux-based software defined radio, oscilloscope, and logic analyzer work on this architecture. For lower speeds you can get away with a microcontroller running bare metal code to do the buffering, but the high speed stuff enters the domain of FPGAs.

Re: I decided to build a nine-bit computer

#17

Post by horsawlarway »

IshKebab wrote: post #10

> The answer to why you would still want to build an FPGA system is (and always has been) speed. > So I quickly gave up on creating something that could only exist on my FPGA board I've been doing some FGPA stuff and I think that's the wrong way to look at it. Yes FPGAs are often useful when you need raw speed but that's not the only advantage over CPUs. You also get extremely low latency and direct control of IO pin…

I agree with you.

I had a brief stint in hardware design, and an FPGA is almost always going to be worse than dedicated hardware for a task, but it's extraordinarily flexible.

Most workflows I saw - you design the hardware on the FPGA (hugely useful for quickly testing and prototyping) then you outsource and actually build a custom chip if you really want speed.

It's also a great polyfill tool - since it can take the place of a lot of other hardware peripherals at a moment's notice.

Re: I decided to build a nine-bit computer

#18

Post by andai »

PragmaticPulp wrote: post #16
sillyquiet wrote: post #6

Regarding the interesting bit (to me) in there about the advantages of FPGAs over an SBC like the Pi (speed)- does anybody know of any blogs or projects where an FPGA's speed helped in a hobby project where software running on an SBC wasn't fast enough? I can imagine a few, mostly real-time projects involving expensive computations (image or pattern recognition maybe?), but I would love to see some concrete examples.

Basically anything with significant real-time requirements or high bandwidth requires an external FPGA or microcontroller. Embedded Linux is great, but if you’re trying to do something like read from a high-speed ADC then the only way to do it is with an FPGA. The FPGA reads from the ADC at precise intervals and buffers the data. The embedded Linux system can then periodically read the buffer with all of the jitter a…

Noob question, in this instance would a realtime OS or a unikernel also solve the problem?
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