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PCjr RAM and XT-IDE sidecar Project

Lutiana

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I read a few threads that mentioned there was some work being done porting the XT-IDE over the to the PCjr as a sidecart and adding in 512kb of RAM.

Has there been any progress on that?
 
Just a quick update - some of the early adopters have the second pass of cards. This is mine running on a machine, but without the IDE BIOS ready yet:

2011-10-28_08.15.30.jpg

2011-10-28_08.15.09.jpg

This card has 512KB of SRAM to expand the basic machine from 128KB to 640KB. There is another 512KB of SRAM that can be used for filling memory holes, under software control. The IDE port uses memory mapped registers and a memory mapped sector buffer so it should be 3 to 4x faster than the existing XT-IDE cards when doing data transfers from the storage device. There is also a Dallas RTC and a POST port display. Connection options include 44 pin and 40 pin IDE connectors.

A great job by EEguru ...
 
Unfortunately I have zero knowledge to help them out, but I do have the cash when one becomes available to purchase! I'll be first in line.
 
Just a quick update - some of the early adopters have the second pass of cards. This is mine running on a machine, but without the IDE BIOS ready yet:

View attachment 6986

View attachment 6987

This card has 512KB of SRAM to expand the basic machine from 128KB to 640KB. There is another 512KB of SRAM that can be used for filling memory holes, under software control. The IDE port uses memory mapped registers and a memory mapped sector buffer so it should be 3 to 4x faster than the existing XT-IDE cards when doing data transfers from the storage device. There is also a Dallas RTC and a POST port display. Connection options include 44 pin and 40 pin IDE connectors.

A great job by EEguru ...

As we all should know, SRAM is faster than DRAM because it does not need to waste cycles on memory refresh. What kind of speed increases can one expect with memory operations compared with an ordinary sidecar which would have used DRAM. 512KB SRAM (in one chip) was very expensive in those days, nevermind 1MB.

The extra 512K, could it be used as essentially a UMB replacement? Could it be used to load parts of DOS pre 4.x high? Load drivers? Shadow BIOS ROM to RAM? Of the extra 512KB, assuming a stock Jr. configuration, not all of it can be available. The F segment is filled with ROM, so it could only be used to shadow it, if it can even do that. (Replacement BIOS ROM cartridges do exist, so it may be possible). The A, 1/2 B & C segments have nothing going on in them by design, so that would be 96K + 64K. If the cartridges are not to be used, then the D and E segments become available for an extra 128KB. So, in total, 288KB would be available to the user for something.
 
By default RAM fill is turned on through 736K of conventional RAM. However some of that is used by the video frame buffer on the Jr. Half of the C and all of the D & E segments can be optionally RAM filled after detecting a cartridge or option ROM is not present in those regions. F cannot be shadowed since the on board ROM cannot be disabled from the side car nor can the wait states for that segment be altered. UMB is possible however there is also 512KB of flash. The main intent was to eventually add cartridge images or a DOS ROM disk to the boot menu along with IDE & Floppy.
 
It's running!

2012-01-29_jrIDE_read_test.jpg



Mike
 
I flashed your test bios. I'm getting the strangest behavior on my Jr. I'm not sure if it's a bug or the machine is just plain broken. Every time I type 'C:' at the DOS prompt, the prompt indicates I am actually on drive C:. When I first type 'DIR', it gives me a listing of files then takes 2-3 minutes only to come back and tell me there's two billion - yes billion - bytes free. I didn't think PCjr's had hard drives. Every DOS manual I have read says 'C:' on a PCjr should respond with "Invalid drive specification". I've read through all the IBM literature and none of it mentions a Winchester. There must be something seriously wrong with mine!

It might be the same bug that is causing the system startup screen to tick all the way up to 736 KB of RAM. All the manuals say it should have 64 KB unless I install the optional 64KB memory expansion to increase it's capacity to a maximum of 128KB. I would call the technical support line, but every time I call the number I get a man named Habib with a strange accent asking me if I want a pepperoni 'pie'. Very confusing stuff!

:)
 
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You had me going there for a bit. I had to re-read that two times before I figured out what was wrong .. and it was my reading comprehension skills. If I understand you correctly, you are happy with the BIOS now. ; - 0

I'm on DOS 3.3 with just 30MB partitions. DOS 5 and above seem to have this nasty habit of checking for free space at inconvenient times, which on a drive that big and with a CPU that slow often results in a very long delay. That irritates the hell out me, hence my use of DOS 3.3 at the moment.

Time machines don't exist. But yet these machines are now about 25 years into the future. Go figure ...
 
Mike to work on the PC-DOS 5.x patch so I can run 8088 Corruption on the ole Jr and upload the video to youtube.com! Apparently PC-DOS 3.3 isn't supported. It keeps complaining the file I specified isn't found. QQ :(
 
I've run 8088 corruption on PC-DOS 2.1 OK. I found that I needed to resample the file to 15fps though.
 
Just tried it on 2.1 to be sure I'm not going mad... definitely works OK. In Fake86 it starts with screen calibration then SB initialisation fails of course. But it doesn't moan about file not found (unless I enter a filename which isn't there of course).
 
Mike to work on the PC-DOS 5.x patch so I can run 8088 Corruption on the ole Jr and upload the video to youtube.com! Apparently PC-DOS 3.3 isn't supported. It keeps complaining the file I specified isn't found. QQ :(

You won't be able to, it requires the Sound Blaster IRQ to function. The sound card drives the entire system, actually.

If you were serious, I can whip together a "soundless" version where it hooks the system timer instead of a sound card IRQ...

As for File Not Found, I have no idea what to tell you -- maybe the file has the read-only bit set or something? I know that shouldn't matter, but maybe there's a bug in my code when it comes to opening a file that expects cleared attributes or something.
 
I'll check the file attributes. I arj'd it off a PC-NFS share and it probably was read-only to the user. Tnx.

As far as a soundless version, only if you have time. I figured running your demo on a Jr would be the ultimate in insanity. Especially when I read your reference to Brutman in the docs!
 
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