October 31st

It's the end of a beautiful challenge...

I knew early on in the #RetroChallege that I had bitten off more than I could chew, and then I couldn't devote as much time to the project as I would've liked.

State of play

I had mentioned on Twitter, a couple of days that it felt like when you know the university assessment project deadline is looming but it's only half done, and the bits that are done aren't working at all...

MIllRACE I/O Module

Build

Yes, it was built. :-)

Keyboard

My test software was showing near-random output for scanning the keys, but you can see the values changing when a key is pressed. Plus, it looked a lot better when I reduced the RC2014 clock speed to 3.6MHz.

I've come to the conclusion that there needs to be a buffer between the Z80's address lines and the keyboard. It was suggested to use a latch, to eliminate timing issues, but that would negate the challange of using the "unmodified" Jupiter ACE ROM. There is room on the prototype board for another 74LS245. If I redesigned the board, I probably would utilise the WAIT signal for a few more clock cycles to get stable keyboard data.

I really do like the look of my keyboard. It's effectively a paper overlay (I haven't laminated it yet) on top of the RC2014 Universal Keyboard.

Speaker

Due to the problems I had with the prototype board, I didn't get the chance to rewire the decoded IORD and IORW signals to the CLC pins of the PIC microchip.

Interrupts

Yes, I was definitely generating interrupts. The firmware on the ROMWBW was definitely complaining about unhandle interrupts. This was why I decided to use my own ROM firmware to test.

And no, I didn't get around to implementing the interrupt tests. Using the "+rc2014 -subtype=sio" target on Z88DK didn't allow for ease of adding your own interrupt handlers, so having to create my own "Interrupt Mode 2" handlers, whilst keeping SIO "UART" capabilities are on my backlog (even if I can't use "stdio").

Tape recorder EAR and MIC

No progress what so ever on that! The PIC on the IO module has pins ready to read and write. My aim is to read the EAR and MIC, and convert it to a hex dump to output through the UART. The board will have a 10-way IDC connector allowing the EAR, MIC, and a UART off-board.

MillRACE Video Module

Build 

The wiring between the PIC and the Z80 Bus is complete (barring any rework needed), but that is pretty much about it. I didn't get the time to work on it more.

ToDo

Things still to be done:

• write the PIC firmware to read data from the system RAM.
• add level shifters between the PIC and the RPi Zero.
• add SPI reading code to my video rendering software to control the PIC

Summary

This RetroChallenge project had been a blast! 

Yes, nothing works -- yet -- but it's been a decent push in the right direction for my project. I probably wouldn't have even reached this stage, if I didn't participate in the challenge.

I've already got the itch to extend the Video module to support ZX Spectrum and other graphics modes...and maybe utilise the WiFi in the RPi to be a kind of DMA WiFi MODEM.

I have learned a great deal. I have also learned that I've still got a great deal more to learn!

So, will I continue this project beyond the challenge deadline?

A whole-hearted yes!