One thing I’ve always found annoying when working with DB9s is that the staggered pins makes them incompatible with matrix board.  The simplest solution has always been to just put the DB9 on the end of a cable, and either solder the cable directly to the board, or use a box header, which has parallel rows of pins.

A few days ago I was hit with a flash of inspiration – and now I can’t believe I didn’t think of this solution sooner! Continue reading →

I’ve recently pushed some changed to the TG68MiniSOC Github repo at https://github.com/robinsonb5/TG68_MiniSOC.  Changes this time round include:

• increasing the system clock frequency to 133MHz.  In order to do this I had to add some wait states to the processor, but the increase in RAM bandwidth makes it worthwhile.
• Adding some more robust filtering to the PS/2 clock signals.  At the faster clock speed I was finding that the mouse and keyboard were misbehaving – it appeared as though there were spurious clock edges causing the receiver to get a bit or two out of sync with the keyboard and mouse.  After trying various tweaks to the PS/2 module’s parameters with no success, I tried running the PS/2 clock signals through the debouncer I mentioned in the post about latching power circuits – and that seems to work like a charm.
• Since two of the target platforms have 32 meg of RAM, and since I now have a Platform Specific register the firmware can read to query how much RAM is present, I’ve moved the base address of the hardware registers.  Previously they were at 0x800000, which is 8 megabytes into the address space.  This works out nicely on the DE1 which only has 8 meg of RAM, but on the Chameleon and CIII board the base address needs to be above 32 meg.  So I’ve changed it to 0x80000000 – or 2GB.  Chances are I’m not going to encounter an FPGA dev board with more than 2 gig of RAM! Continue reading →