Modifying microcode

[Jon Elson]

On 05/30/2018 08:19 AM, Kyle Owen via cctalk wrote:
> Has anyone attempted to reassemble and update the microcode on a MicroVAX?
>
> Seems like there's enough stuff here to possibly do it:
> http://simh.trailing-edge.com/semi/ucode/
>
> I'm thinking about trying to find a microcoded architecture to play with
> before I design something around the Intel 3000 series.
Intel 3000?  WHY!

I'd get an FPGA development board and download Xilinx's 
webpack software.  It would not take real long to design the 
basic microcode engine, and then you could develop some 
application microcode in parallel with the hardware, adding 
whatever feature to the hardware you needed when the need 
came up in the microcode.
> I've got a MicroVAX 3800, so I suppose I could run MICRO2 to assemble the
> aforementioned microcode. But then what? I assume PALs would have to be
> burned to implement the new microcode. Or is it more complicated than that?
>
PALs?  I don't think the 3800 microcode was in PALs.  I 
think it was in the CPU chip.  There may have been a patch 
array that allowed a very small number of microcode words to 
be overridden.

Jon