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Homebrew Computer musings- Hopefully part I of a series.


Veteran Member
Dec 28, 2011
Recently I got my amateur radio license... one result of that is that I want to at least partially build my own radio- either SDR or a small home computer to handle digital operating modes. Sure, a DSP or FPGA dev board would be more than up to the task, but I feel like I want to create something custom to sharpen my skills and try different things as well.

My computer architecture knowledge hasn't been at its peak since... well, since I had to build a toy CPU in Verilog for a class :p. It could add, subtract, jump unconditionally, jump on condition, move, load, store, and not much else. Making a new system from components would bring my knowledge of how the timing of the control/address/data buses interact with each component back up to speed. In particular, I've been interested in how I would implement a system with DMA and multiple address spaces- something I was never taught to do in my class simply due to lack of time.

I do not have ANY real design laid out. My processor of choice would be the 65816 in Native Mode- it has a simple assembly language and a number of features that I feel are underused, and I just have fun writing code in it. Other constraints would include the following:

  • Support cycle-steal DMA implementation using either a dedicated DMA controller or coprocessor (65C02) to maximize bus bandwidth. If the latter, 32kB would be a window into the 65816 address space, the upper 32k would be relevant code/data. Kinda like the Z80 access to the 68k on the Genesis actually... except unlike the Z80, this 65C02 can't take control of the 65816's bus except during DMA.
  • Do not use FPGA/CPLDs
  • Use only parts which are still produced as of 2014
  • Does not need to be limited to ham radio applications

So this is more of an education exercise than anything to see if I can get this right.

Whether this idea gets off the ground remains to be seen- and it won't be any time within the next few months. However, I figure I should mention it now so I can get some feedback and as a reminder to myself. I'll draw a simplified circuit soon.