Best DOS to use on the Pcjr?

[alanh]

Also we should just jump on Jay's Discord server one night and hack out a plan.... I'm on a planet that is currently in world-wide lock down. So I'm available anytime!

[Brutman]

I looked at the annotated versions of jrconfig but I didn't see any writes to the port that controls the mapping of the video buffer, which I thought was strange. I looked in both versions. I'm going to examine my binaries to try to find where that is done; it could also be hidden by a call somewhere into the BIOS but that seems unlikely.

As for the double boot, if it is that easy to remove then good riddance.

[Trixter]

I was looking in the tech ref when I wrote my post. I also looked at the annotated jrconfig assembler listings that Alan posted, but strangely I did not find the OUT commands to the port needed to move the memory window.

That's because jrconfig.sys is using the BIOS to do it, specifically Int 10/AH=05h. More info: http://www.ctyme.com/intr/rb-0095.htm

I do have a byte-perfect fully annotated jrconfig.sys 2.14 disassembly located at:

That is totally rad! Nice job, that must have been at least 4+ hours of work. Saves me the trouble.

[alanh]

That's because jrconfig.sys is using the BIOS to do it, specifically Int 10/AH=05h. More info: http://www.ctyme.com/intr/rb-0095.htm

As Jim points out... It's done in jrconfig.sys in the function _reset_video_page. The location of the active video page is set in the global variable _video_page. The reset call is then placed inline in both Int10h set video mode and all the DOS exit interrupt calls.