Retromaster’s Electronics Projects

…related to old computers and other assorted stuff…

UFE A500 Keyboard Daughterboard 2

Posted by retromaster on June 10, 2010

I’ve fixed the problems in the first A500 keyboard daughterboard I’ve made. Here are some images of the new one, including one that shows how it looks when installed on an A500. At the moment, it works fully with the UFE mainboard. The missing I2C slave writes have been implemented. UFE is fully controllable from the A500 keyboard.

There is one problem, though. The Amiga keyboard protocol requires that the transmitted key event be acknowledged by the Amiga once the full 8-bits of data has been received. If this acknowledgment is not received, the keyboard goes into “lost sync” mode. It stops sending key events, until sync is restored.

Normally, this behaviour poses no problem for UFE, but in some rare cases, some (poorly written) cracks/loaders temporarily assume complete control over the system, causing the acknowledgment to be not sent. For example, the Turrican 3 cracked loader flashes the screen to request the user to swap disks. When in this mode, the loader only checks if the disk is replaced and ignores everything else, including keyboard events. Since the keyboard becomes unusable in this mode, it becomes impossible to activate UFE.

I can think of some solutions to this problem. Probably, one of the more robust ones is to check for the “lost sync” condition in the keyboard daughterboard firmware. If the host fails to respond to the “lost sync” condition after eight 1s have been clocked in, let the keyboard daughterboard acknowledge the last key event. Since the keyboard always retransmits key events that are not acknowledged, no key presses will be lost. Eventually, the host will be able to handle keyboard events properly, and everything should be back to normal.

On a side note, to manufacture this new board, I’ve used a new “drilling technique”. Instead of aligning the toner transfer paper to CNC drilled holes, I did it the other way around. I first did the toner transfer (with holes in pads) and etched the board. Then, using CNC coordinate measurements for four corner pads, I computed the transformation from PCB software coordinate space to etched board CNC coordinate space. This transformation compensates for scaling, translation, rotation and shearing. I’ve written a Python script to do the computation and integrated it within my g-code converter script. As the PCB scans show, the results have been excellent.

I’ll soon update my “Making PCBs” page with all the new experiences I’ve obtained and I’ll release the Python sources for the scripts I use. I am also going to take some scans while I make the new PCB revision for UFE and update the page with those as well. They should be quite an improvement over the poorly lit photos I’ve got there right now.

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