Mike's PCjr Page

I'm going to take a stab at optimizing the sector read at least tonight. I think by tomorrow night I can have a test bios in-place that does minimal effort with respect to int13h. I would like to see DOS booting off the HD before I start making board changes. Sorry for the long delays. Small windows...

While trying to exercise the ATA access, I had the thought of timing sector reads (at an ATA command/register level). To my surprise, I'm only getting about 68 KB/s reading 63 sectors at a time (1 head). Watcom is doing a horrible job at optimizing: static void _xfer_sectors (uint16_t cyl, uint8_t h...

Yeah. Thanks. I have the printed manual but it's an hour away at the house. Thanks for sending it

The upper address lines and control strobes come directly off buffers in-front of the CPU. The only other possibility I see (besides a side-car bug), are latches, not buffers, that are potentially driving the bus through a buffer that separate the ROMs, carts, and video RAM (the 'X' signal variants)...

It also appears I'm not going to be able to replace the MB ROM chips with pages from side-car flash. I was hoping this would allow people to copy the JR BIOS into either an A or B image in flash (dip switch select-able) to facilitate either patching your JR BIOS or developing a new one. I checked an...

IDE: Yes all the IDE code is just in a dinky test app (eg. send 0xec to the command register, read back and dump the sector). Yeah, most of the work is done. However given the number of specific features to JR-IDE and not needing most of the general features of XT-IDE, it might be better to fully cu...

It seems as if either A17, A18, A19, MEMRD, or MEMWR going to the side-car expansion slot is gated off on the motherboard somewhere whenever the CS lines go active to the cartridge slots. I'm not sure why IBM wanted to do this as it takes active circuitry to do it (buffer w/ strobe exclusion conspir...

OK, I'm at a bit of a cross-roads on how to proceed. Using some rough test code I've started proving out different pieces of the board so I can be a little more confident the next spin of the board will not have any other show-stopper problems. - The RTC works. I wrote a quick utility to set DOS tim...

My time sheet this week had 65 hours. :( However I'm currently doing some basic prove outs of the board. Where can I get a later version of DOS (than 2.1 which I'm running)? Preferably a patched version of 5.0 or 6.x? Of course the vanilla 6.22 hangs. I did write an extensive memory test which inclu...

Ok, I think I'm finally getting back to this. Sorry for the delays. I'm all moved into the new place and settled. I tentatively have a few hours each night this week to give it ago. I'm pulling down the source tonight and trying to get a MASM setup working to at least be able to rebuild. Along with ...