Pi-based Co-Pro on the cheap - 100MHz 6502 for £10? (now over 400MHz)

[jgharston]

A further point on the PDP11 CoPro, was there ever any development on implementing seperate user and kernel space?

Additionally, there's been a few things I've been thinking about adding to the Client, but there are only six spare bytes left, which are likely to be used up fixing the above-mentioned bugs. So, I've been thinking of an option to double the Client ROM code to a whopping 4K. Would there be a simple way for an updated PDP11 CoPro implementation to realise whether its booting with a 2K ROM or a 4K ROM?

At the moment the system is designed so that the ROM code occupies memory at &0000 upwards, on RESET the PC is set to &0000, the first ROM instruction is a jump to high memory, and on reading from high memory RAM is paged into memory. The Client code expects RAM to run all the way up to the start of the ROM, so with a 2K ROM that's RAM all the way up to &F7FF.

[hoglet]

I've been doing some deep testing of PDP11 BASIC, and uncovered a couple of bugs with the PDP11 Tube Client.

I can include these in the Indigo release if they are fixed within the next two weeks.

A further point on the PDP11 CoPro, was there ever any development on implementing seperate user and kernel space?

Not that I recall.

Would there be a simple way for an updated PDP11 CoPro implementation to realise whether its booting with a 2K ROM or a 4K ROM?

It will require a small code change to these two lines:
https://github.com/hoglet67/PiTubeDirec ... dp11.c#L88

At the moment the system is designed so that the ROM code occupies memory at &0000 upwards, on RESET the PC is set to &0000, the first ROM instruction is a jump to high memory, and on reading from high memory RAM is paged into memory. The Client code expects RAM to run all the way up to the start of the ROM, so with a 2K ROM that's RAM all the way up to &F7FF.

That's not quite how the current PiTubeDirect PDP-11 Co Pro works, but it should be compatible. So what happens on PiTubeDirect is there is not really a ROM at all. There is 64K of RAM (less the I/O) window. On reset the PDP-Client code is copied by the emulator into RAM at &F800 and then executed from that address. See the above line.

Dave