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Source code for BJL ROM ?


SainT
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Is the source code for the BJL dev ROM anywhere?

 

Basically I'm just after a working starting point for doing some remote development on actual hardware, but I'm after a ROM based solution as I intend to use this to start playing around with the new JagSD cartridge hardware when I get the first prototypes done.

 

I'd prefer the source if available, just because I intend to use the synchronous serial port for reliable USB comms rather than joypad.

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Hmm, I did have a look in the bjl zip before, but couldn't see anything which looked like a replacement boot rom. I'll have to have another look...

 

I think that might be the uploader only, the server code is provided as a .BIN - your best place to look would be the Jagware.org forum.

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I do have the source for the ROM (GT Turbo actually met Bastian Schick a long time ago and asked him), but I'm not sure I'm allowed to distribute it ; the fact Bastian didn't provide it on his site lets me think it's not supposed to be public.

 

IIRC the code is pretty spaghetti-like, there are few comments and they are in German.

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Thanks all, I managed to sort it. I just took the first part from the boot ROM which sets up the video registers and added that code to the beginning of the "Hello World" sample program, then setup the 68000 SSP and PC values. This now works when flashed to the boot ROM.

 

Now to figure out the best way to talk to the PC...

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You have several options:

 

- using the joypad port. Forget about the method used by BJL, it's unreliable, especially on modern machines. For the Jagtopus board, I wrote my own protocol which works reliably, but it's not very fast.

On the hardware side, if you want to support USB, you need either a custom solution using a microcontroller (or possibly just a USB bridge chip like the FT232 in parallel mode -- not tested). I did something like this with the Catnip Cable.

Standard USB-to-printer cannot be used directly since they don't support bit banging, but emulating the Centronics protocol on the Jaguar may work (I looked into it a few years ago, got some interesting results, but never finished it).

 

- using the asynchronous serial port. Jaguar -> PC works fine ; PC -> Jaguar is problematic because the UART receiver in the Jaguar is buggy. You can either attempt to avoid the bug condition, or cheat. Easiest solution on the hardware side, since you only need a JagLink and a USB-to-RS232 cable, or even a USB-to-5V TTL serial cable you can connect directly to the expansion connector on the back of the Jaguar. Drawback: even at 115,200 bps, this is slow.

 

- using the synchronous (I²S) serial port. Interesting idea; I don't think it's been done before, and it would be pretty fast. It indeed works, since I once connected an external CD player (by tapping the I²S signals on the audio DAC chip) to the Jaguar, played a CD-R with data converted to audio tracks, and got the correct data on the Jaguar. You could use a USB audio chip, but latency and audio mixing on modern OS could be problematic. Otherwise a custom solution using a microcontroller with I²S (or even SPI) support should work. Depending on the implementation, you may not be able to stop the clock, so you may need a protocol which tolerate "filler" bytes when no communication is needed and fast enough hardware to avoid buffer underflows/overflows.

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Yep, the synchronous bus is the way I'm going to go. 32bit mode with the Jaguar as slave and a Teensy driving the bus and accepting the data over USB.

 

It's a bit excessive going to all this length for something which I guess only I will ever use, but I will publish what I write in-case anyone else wants to do it! :)

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