MAMEWorld Forums - EmuChat - Re: Looking to get an obscure console (monon color) emulated

> https://docplayer.net/52724058-Ax208-product-specification.html#download_tab_content
> > claims 96Mhz 8051 with single cycle instruction timings.
> >
> > could be challenging, but definitely something I can start research on with the
> right
> > resources, at least see how much valid code they run etc.
> >
> > anyway, dropped you a PM, would be good to get at least the basics of this in with
> a
> > Software List for the dumped ROMs
>
> Sent

ok, been poking around a bit, I don't think it's going to be a quick one to emulate, but at least having something we can work with makes it a possibility.

there are a number of annoying factors, first of all the 8051 has additional 16-bit opcodes and registers, these are mentioned by name in the datasheet, but the encodings are not given. the code clearly makes use of these, they're all prefixed with an 'A5' byte which is an illegal instruction in regular 8051

Code:


006d4e: 54 fc     anl   a,#$FC
006d50: 14        dec   a
006d51: f0        movx  @dptr,a
006d52: 90 01 b1  mov   dptr,#$01B1
006d55: a5        ill/rsv    << illegal opcode in 8051, should encode as a5 04 for this CPU
006d56: 04        inc   a  << actually 2nd byte of above
006d57: e0        movx  a,@dptr
006d58: 64 01     xrl   a,#$01
006d5a: f0        movx  @dptr,a
006d5b: 80 a8     sjmp  $6D05
006d5d: a5        ill/rsv   << illegal opcode in 8051, should encode as a5 00 for this CPU
006d5e: 00        nop  << actually 2nd byte of above
006d5f: e0        movx  a,@dptr
006d60: 04        inc   a

Second, while there might not be a BIOS rom, there's definitely some kind of internal bootstrap so that it can copy code from the SPI Flash into RAM before booting, and the exact mapping of the code copied is unclear (although I have identified where a number of blocks go based on long jumps and return statements)

Third, the documentation doesn't really even cover how the video hardware, Jpeg decoder or anything like that works, so it's going to be a pure reverse engineer from behaviour challenge, which we're used to, but means things are unpredictable.

Definitely a very interesting little system that I wouldn't have known existed had you not posted about it tho, it might end up turning into a little project for the course of next year depending on how much progress I'm able to make. Looks like the CPU / SoC manufacturer mainly made CPUs for SD card controllers, MP3 players etc. Although they do apparently have a 32-bit chip with video capability in their range too. Pretty much all the rest of their range do have onboard ROM tho, which is a shame because I'm sure some of that tech will show up one day and we'll want to emulate it too and extracting internal ROMs can be a nightmare, especially on custom parts.