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TSR vs DEVICE= (Announce)

posted by Arjay, 20.06.2010, 12:48

> This might be true for some old DOS versions.
 I believe a lot of this will be true for versions prior to DOS version 4 (/3.2). It would also appear that earlier DR DOS Plus didn't implement the Int 21h 44xxh IOCTL side of things, however there are no similar comment re DOS internal IOCTL, e.g. Int 2F/AX=122Bh etc.

As I noted earlier on this forum the PSP was introduced in DOS version 3., obviously as you know SYS drivers start at org 0h so don't have their own PSP which contains "helpful" things like environment, fcb, command-line parameters etc.

As Jaspeth points out there is a the DOS PSP which should also be obtainable via either Int 21h ah=61h or Int 21h ah=52h.

However you are right things are easier from a TSR side. Indeed don't also forget there is the far easier (later DOS) option of coding an EXE device driver like EMM386 which more TSR than true SYS device driver. When I wrote an EXE driver sometime back I used Michael Tischer/(PC Intern)'s EXESYS.ASM as a reference point and that was at least a fairly straight forward exercise then. Certainly I would recommend PC Intern as a really good book to have on the bookshelf - my now very worn copy is from 1993 (there were newer versions). I would however agree with the comments on the Amazon link above, e.g. in my own book the block device table has the heading "header of the character driver". Still in technical books this detailed these types of error will always creep in.
Note: it isn't the only book I have on which covers device drivers in detail but it is the one to hand and has 40 pages (out of 1356) on device drivers and 44 pages on TSR's, memory management/PMode are separate sections again.

Also noted elsewhere I did also write some SYS drivers a long time ago. Indeed the reason I have been adding SYS driver support to RJDUMP is I have something else that I've been working on not exactly a WRAPPER.SYS replacement but it could provide similar if I choose to use it that way.

Indeed I am planning to use the release of RJDUMP to "test" some of my other work further but this time with device drivers as compared to say bootsectors which is what I was testing my work with prior to getting taking this step to the left. Still the long and the short of it is I'm doing a lot of chicken before the egg coding at the moment, so I do know where you are coming from and am actually interested in finding solutions to the apparently impossible.

Still I would like to directly apologize re my earlier ill informed thoughts re combined drivers as I was forgetting about some of the problems that exist in the middle of DOS loading having worked around some chicken and the egg situations elsewhere (e.g. prior to DOS loading or after DOS has loaded) but not yet in the middle of DOS loading as required here. So apologies for that!

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