So SD card support has been extremely frustrating, to the point of complete despair. I'm still unable to make it work as I wanted it to, but I guess I managed to discover a narrow path, which if followed carefully allows safe passage from initial directory loading to loading file content, almost always. I'm still unable to show OSD and access SD card at the same time.

In the meantime I have found some really useful bits of code that should be standard in ESP32 SDK but they aren't:

• PSRAM allocator by atanisoft psram_allocator.h: allows allocating data for vectors in PSRAM
• better_readdir() with FatFs FILINFO struct access, allows for quick directory listing: instantly get file sizes

better_readdir() is particularly important because stat() in FatFs is excruciatingly slow, it takes 1-3 seconds just to get one file size. Why? Don't know.

I also made good use of Graphics from @bitluni ESP32Lib. Excellent library, not perfectly optimised but easy to make modifications to. I implemented BGR233 canvas and added clipping. My OSD buffer is thus fairly small as it's in 8-bits. This allows it to be stored in DRAM. It's copied to screen using routine similar to the one that copies the main Vector-06c buffer. That's not ideal because it's fairly CPU-heavy, but I just love it when it's shown next to the main screen.

This also made me add support for 1:1 horizontal scaling of the main screen, which is switched on when OSD is displayed. It could also be made an optional mode without OSD.

Curious bit:  a program that only has nops, for example when it's empty RAM, is a worst case for the emulator because this means maximum amount of instructions per scanline. When something like this is executed, the OSD becomes really reluctant to react to user input. Some programs even have flicker at the top left corner of the screen. Something to deal with at some point later.

So far only ROM loading is implemented.