Gen-X 68040

At present, the GenX is functionally equivalent to an A2560K without the keyboard.

Manual

Latest FPGA release:

Notes:

• Both displays show logos, but only display B is responsive.

Startup

• On hard-reset, the FPGA copies the first 64k of flash to $0.
• Post-upload reset leaves that block alone, so you can upload code there.
• Remember that the 68040 has THREE stacks: user, supervisor, and interrupt. Reset puts you on the interrupt stack.

Memory

• With the latest pre-release FPGA load, burst access to SRAM and flash works in all modes. This enables use of the MMU and all of the caching modes.
• If you wish to enable the caches, be sure to mark the I/O space as "serialized". This should technically be done even if you aren't using the dcache.
• At present, the DRAM is not stable.
• To test your own OS code, upload it to $0000:0000.

I/O

• The SD Card detect bit doesn't appear to work (always thinks a card is present).
• If you wish to enable the caches, be sure to mark the I/O space as "serialized". This should technically be done even if you aren't using the dcache.
• Text display memory is byte-access only.
• VRAM writes go through a fifo. At present, there is no way to read the VRAM (which, IMHO, is fine), and if the fifo fills up, the graphics engine will pause drawing to work the fifo.

Math Co-Pro

• Unsigned divide seems broken.
• When running out of iCache, you need a NOP between writing the signed divide registers and reading back the result.

vasm

• The 68040 MOVEC cache and MMU control registers are there, but typically without the last letter (R for Register).
• Auto-alignment rules are brain-damaged: the assembler will re-align instructions but not their associated labels, and won't even warn you if constants are mis-aligned.
  • Ha! The -align option forces natural alignment of data. This fixes most of the problems. Just be sure to manually re-align after any byte data.