Hi,

As I mentioned in another post, I'm attempting to port the (freely distributable) OCM source to my own hardware.

I'm having trouble understanding how the OCM actually boots.

The only ROM included in the OCM is a 512-byte IPL rom. I've started disassembling it but not knowing much at all about the MSX, I've really got little idea what it's doing.

Could someone explain in a few sentences how the OCM boots?

FWIW The first thing the IPL ROM does is copy itself to $F000 and transfers execution to itself up high. From there I really can't tell much more -= too many "magic" numbers.

So does it require the BIOS/BASIC ROM to be present in one of the slots? Or does it bootstrap the ROMs from SD/MMC card?

Any explanations would be greatly appreciated.
Regards,
Mark

FWIW, I've been reading through the source code, and can now see the OSD when I press <F12> a few times... so something's running!

There's also a 256KB hex file with all the actual ROM. I think it's included in the final image. (seems like a waste of fpga space, but that may just be my lack of understanding of the device). This rom must be copied into the dram. Maybe the iplrom has something to do with that. I haven't actually analysed that part of code myself.

There's absolutely no way the roms will fit inside the EP1C12, which only has about 27kB of block RAM.

I suspect the hex file you speak of is used to program either the EPCS4 (most likely) or an SD/MMC card, and the IPL ROM copies the contents to SDRAM. There's logic in the image to access both the EPCS4 and SD/MMC.

I just need someone who has an OCM to tell me if it'll boot into BASIC without an MMC/SD card in the slot!?!

Regards,
Mark

I think it's the first option then. Because I haven't seen any reference to a file that needs to be present on SD.

tcldev,
so, can you tell us how ROMs are implemented ? Especially now, when you have your board running ?

They're stored in the EPCS4. More details coming very soon!