Sega System 24 SD Card progress Part 2

Swapped the switching FET to an open collector 7406 (I didn’t have an LS handy) and I was able to reduce the delay in the read considerably.

Reading the directory from the SD card works which is cool.

As the SD/FAT code needs to run in the System24 bios, it all needs converting to 68k assembler. After a few evenings work, the code to interface to the sd card is written but still needs debugging on real hardware. FAT16/FAT32 (or maybe just FAT32) code to be converted next.

The beauty of having the code working in C is that I can just replace each function with it’s assembler version and test each one. (after realising I needed to create some trampoline functions to convert the stack passing method to a more typical assembly call method.. unless there’s a compiler function to use register passing.. I wonder..)

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Sega System 24 SD Card progress

After spending a ton of time researching sdcard interfacing, perils of voltage shifting and with the help of Charles MacDonald getting the Genesis C compiler working on System 24,  I have successfully read a file from a SD Card. whoo hoo.

This is only proof of concept as the hardware is very slow receiving data and all the C sdcard and fat16/32 code will need rewriting in assembler. Hopefully a change from a FET to a 74ls05 will improve the speed.