How about DOS in ROM?

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How about DOS in ROM?

Postby alanh » Wed Nov 20, 2013 5:16 am

There's 512 flash on JrIDE to play with. What about an int13h handler for the other 496K (-16 for BIOS) and PC-DOS 5.0 in ROM? Maybe leave room for a more comprehensive cart ROM directory as well?

Remember there is a second 16K ROM window that can be enabled and then panned around the full 512K flash area.
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Re: How about DOS in ROM?

Postby Trixter » Sun Nov 24, 2013 9:57 pm

I'd love for the other 480K to be accessible as a RAM drive or similar. Not so sure how useful DOS in ROM is, though... it seems to open up a can of worms (how to replace/update? where would config.sys and autoexec.be read? How to boot your own? etc.).
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Re: How about DOS in ROM?

Postby alanh » Mon Nov 25, 2013 8:50 am

I was thinking of a int13h handler - basically a 480K hard disk as drive C that would get it's blocks by fetching them from ROM. You could even add write support since it's flash. However it's tricky. The erase sector size of the flash part is 4K. So to update a 512 byte block, you have to read the 4K, copy the 512 into the right spot, erase the sector, and write the new one back. It's a window where the disk can become corrupt if you lose power. Also it's inefficient. So it should be done either on occasion or pre-prepare the DOS disk image and flash the whole thing at once with the existing utility.
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Re: How about DOS in ROM?

Postby jmetal88 » Mon Nov 25, 2013 1:54 pm

I sure wouldn't mind having DOS in ROM. I think it'd be pretty neat, even if it made it awkward to change the boot procedure.
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Re: How about DOS in ROM?

Postby alanh » Mon Nov 25, 2013 4:26 pm

Dos in ROM would be just another option on the boot menu. You could skip it if so desired.
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Re: How about DOS in ROM?

Postby Brutman » Mon Dec 02, 2013 9:41 pm

DOS in ROM is one option but it is fairly disruptive to the BIOS extension that is being loaded. The new INT13 BIOS would have to have a new path in it to do the FLASH reads/writes instead of the register I/Os it is doing now.

A slightly less intrusive option is to create a block mode device driver that allows you to access that unused FLASH storage as a drive letter. The nice thing about it is that it would be persistent; a drive letter dedicated to just your utilities would be one option.

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