PhaseLoom: A Software Defined Radio Powered by the Chip used in the Commodore 64, NES and other Early Home Computers
The MOS Technology 6502 is, by today's standards, an ancient chip, having just turned 50 this September 8. It was the chip behind the early age of home computing, powering iconic systems like the Apple I & II, Commodore 64, Atari, and Nintendo Entertainment System. It is, therefore, fascinating that someone has managed to use this chip as a core component in a modern software-defined radio system.
Over on his blog, Anders B Nielsen describes PhaseLoom, a 6502-based "Quadrature Sampling Detector Phase-Locked Loop SDR frontend". Realistically, we want to point out that the 6502 isn't actually doing any digital signal processing (DSP). The 6502 is used as an assembly programmed controller for a SI5351-based local oscillator and multiplexor chip that generates IQ data. Piping the IQ data into a PC with a soundcard is still required to actually get data out. However, Anders notes that he eventually hopes to get some DSP running on the 6502.
With the setup he is currently able to tune just to he 40m band, noting that performance isn't great, but at least it works!
Anders' video below explains the entire design and concept in detail, and we note that he is currently selling a full kit on his store and has uploaded the schematics to GitHub.
The Commodore 64 used the 6510.
A 6510 was basically a 6502 with 6 more port lines for memory switching. This new device isn’t using the same 40 pin Mos dip chip any more than the 6510 chip, but essentially it works the same. Still, the 6502 instruction set is the same.
Many of us cut our microprocessor teeth coding 6502 (on the Kim 1, or Sym 1 boards), vic 20 and other systems. We had to be clever to make useful programs work in 1, 8, 16 or 32k at the 1 mhz clock rate. I’ve often thought modern systems are wasteful of system space, but the kind of optimization we did back then is very expensive these days.
“…the kind of optimization we did back then is very expensive these days.”
The priority for companies now is time to market. Development is faster if you use existing libraries and let the consumer pay for the memory and fast processor to accomodate the code bloat.
The first SDR I saw was the “softrock”. It used the SI570 Oscillator module.
This version, by using the SI5351, requires an external Oscillator source.
Other than that, they are remarkably similar.
It’s “Anders B Nielsen”, BTW.