The EightThirtyTwo ISA – Part 9 – 2019-10-28

Having managed to get the CPU working well enough to run a Hello World program, I’ve since persuaded it to run the LZ4 decompression program I posted a week or two back, too – and was pleasantly surprised to find it running happily at 133MHz on my DE2 board.

I’ve been pondering how best to handle interrupts on this CPU, and realised that I’ve painted myself into a bit of corner by using the tmp register as a link register when branching; this means that without adding some kind of temporary storage register or stack logic especially for the task, I can’t change the program flow externally – such as in response to an interrupt – without losing the contents of the tmp register.

The EightThirtyTwo ISA – Part 8 – 2019-10-20

Over the last few weeks I’ve been working on a VHDL implementation of the EightThirtyTwo ISA, using the excellent combination of GHDL and GtkWave to develop, debug, rip up, start over and ultimately produce something capable of sending “Hello, World!” to a UART.