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HIMEMV2 or equivillent PROM

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  • per
    replied
    you can run program files from config.sys, at least in later versions of DOS (unless I'm slightly mistaken).

    Leave a comment:


  • Chuck(G)
    replied
    Per, the test has to be made before the first driver loads high. So it's got to be in a device driver.

    Leave a comment:


  • per
    replied
    the following code will write to the entire D000xxx segment. The program you will need should include all of the extra segments of RAM above the 640K limit in your system.

    Code:
    ; Write to RAM segment
    mov es,D000h ; Set target Segment address
    xor ax,ax    ; Clear ax, will be the word written to RAM.
    mov di,ax    ; Start at offset 0000h in target segment
    mov cx,8000h ; Number of Words to write, 8000h = 32KW = 64KB
    rep stosw
    
    ; Terminate program
    ret
    Last edited by per; December 7, 2011, 10:46 AM.

    Leave a comment:


  • Chuck(G)
    replied
    Look, the guy who wrote the UMB software that you're using did a commendable job--it's well documented and the source code is included with the driver.

    But I have a quibble with him requiring you to patch the addresses of your UMB areas into the driver. Far better would have been to parse it from the DEVICE= line, put them into the table, then write/test them (the way that some versions of HIMEM.SYS do).

    I could probably do it in an afternoon--it's not difficult code, but I've already put in a couple of afternoons on a project that I have no use for.

    If you can't recruit someone on the list with simple assembly experience, that should tell you a lot about the members of this forum (and probably a ton of others).

    You might also work on learning x86 assembly yourself. There's no shortage of information out there.

    Leave a comment:


  • modem7
    replied
    Immediately after PC power on, the contents of RAM is somewhat random. Certainly, in a good percentage of RAM addresses, the contents of the PARITY bit chip is not going to reflect the parity of the contents of RAM chips bits 0 to 7. That is why one of the things that the POST does on power up (after setting up refresh, and before enabling the NMI) is to write to all RAM addresses that are parity checked. The act of writing to each address will set the correct value into the PARITY chip.

    RAM in early video cards is not parity checked, and so I agree with Chuck in that the POST is probably not doing its 'initialise parity bit' routine past the 640K mark.

    And so at computer power on, after the POST, your block of RAM has a quantity of addresses where the PARITY bit is incorrect. For some of those 'parity chip contents incorrect' addresses, whatever you are loading into the RAM will perform a write to the address. No issue there, and in the act of writing, the PARITY bit gets initialised to a correct value. But in some cases, 'parity chip contents incorrect' addresses will be read before they are written. For each of those, a parity error will be generated.

    A warm boot is not going to change the situation much.

    As Chuck alluded to, before you access your block of RAM, some code needs to run that writes to every address in your RAM block. I'm confident that that is a fix.

    Disabling the NMI will work too, but has at least a couple of disadvantages:
    1. If a RAM chip later becomes intermittent, you're not going to be alerted to the fact (via a PARITY error message).
    2. Can't use an 8087 (it uses the NMI).

    Whichever path you choose (write all RAM, or disable NMI), it has to be done before any code reads a 'yet to be written to' address in your RAM block. And so, as Chuck suggested, a dummy driver (that writes to all your RAM block, or disables NMI) loaded early in CONFIG.SYS should be the answer.

    Leave a comment:


  • ibmapc
    replied
    Originally posted by Chuck(G) View Post
    The easy way is to write a bit of code to mask NMI. See here.
    I'm still lost. Would this be done with DEBUG? I haven't a clue where to start. Anyone want to help me. Or, at least point me to a tutorial that will help me learn how to do it?

    Leave a comment:


  • Chuck(G)
    replied
    Originally posted by ibmapc View Post
    Is there a way to disable parity checking in dos, or would the BIOS need to be modified? I can't find anything in the limited DOS documentation that I have.
    The easy way is to write a bit of code to mask NMI. See here.

    Leave a comment:


  • ibmapc
    replied
    Originally posted by Chuck(G) View Post
    My guess is that the POST routines don't write memory above 640K (why would they?). So, when the next read (after a cold boot) happens, you get a parity error.

    You could disable parity checking or have a dummy driver that writes the upper 128K before it aborts.
    Is there a way to disable parity checking in dos, or would the BIOS need to be modified? I can't find anything in the limited DOS documentation that I have.

    Leave a comment:


  • Chuck(G)
    replied
    My guess is that the POST routines don't write memory above 640K (why would they?). So, when the next read (after a cold boot) happens, you get a parity error.

    You could disable parity checking or have a dummy driver that writes the upper 128K before it aborts.

    Leave a comment:


  • ibmapc
    replied
    Update,
    Although it works, it's not without glitches. First durring a cold boot, USE!UMBS,SYS loads (umb memory handler) and the display shows;

    PARITY CHECK 1
    ?????
    A0000

    It then start loading drivers and such to upper memory and all works fine. However if I do a warm boot(CNTRL+ALT+DEL) then the PARITY CHECK 1 doesn't come 'till after drivers and tsr's are loaded and the system hangs and will only recover after power down. Also, at this point the display shows;

    PARITY CHECK 1
    ?????

    Note, the A0000 is not displayed as it was durring the cold boot. I figured that was pointing to the begining of EGA RAM, so I swapped out the EGA Wonder with a spare EGA Wonder and got the same results. So I tried the original IBM CGA Adapter, same thing. Next I relpaced all the PARITY RAM chips, still same results so I systematicaly replaced each RAM chip on the MOBO(those of you familliar with the insides of the 5155 know what a pain that was). So now I'm thinking it must be a timing issue or something. I wonder if there is a way to keep the system from doing the parity check on that portion of RAM.

    Greg

    P.S. The problem only shows up if I make a change to CONFIG.SYS or AUTOEXEC.BAT to change whats being loaded high.
    So maybe the problem is that UMB is not being purged or re-initiated durring the "Three Finger Solute".
    If I do a CNTRL+ALT+DEL without making changes, it reboots without the parity check coming up and all runs fine.
    Last edited by ibmapc; December 5, 2011, 04:20 PM.

    Leave a comment:


  • ibmapc
    replied
    Originally posted by pearce_jj View Post
    Great to hear it's working!



    A bit off-topic, but checkIt didn't find the extra 128K in the 1400. I also found an original Tandy DOS disk for it, but alas can't see any drivers for it on there either!
    I believe Checkit v 3.0 was the first one to have a memory map feature. Thats where I was able to see the "reserved" area which is the space between 640k and 1meg

    PM sent

    Leave a comment:


  • pearce_jj
    replied
    Great to hear it's working!

    Originally posted by pearce_jj View Post
    I have a Tandy 1400FD outside which has 768K RAM from the factory, so I guess it used a similar trick (V20 CPU). I'd be very interested to get a copy of Checkit3
    A bit off-topic, but checkIt didn't find the extra 128K in the 1400. I also found an original Tandy DOS disk for it, but alas can't see any drivers for it on there either!

    Leave a comment:


  • ibmapc
    replied
    I FOUND IT!!
    After searching and scouring the internet as well as these forums, I found a handler that actually works on the XT. It's called "Use!UMBS". Awfull name, but it works. I now have 128k of UMB. I am able to load a lot of drivers and tsr's up there. With MS Network Client with Netbeui all loaded high along with a bunch of other stuff I have 576k of base memory available and there is still 11k of upper memory free!! If your interested, here's THE LINK. This is awsome. UMB on an XT without an expensive memory board!! Thanks again Chuck(G)!!

    Later,

    Greg

    Leave a comment:


  • pearce_jj
    replied
    Originally posted by ibmapc View Post
    It works! Checkit3 now finds(and tests as good) 128k of "Hi RAM" in the D000h to F000h region. Now, I just need to figure out how to make use of this chunk of ram. I've been un-able to find old versions of QEMM or QRAM. I'm not sure that either of these wold work without a LIM 4 Board but I was hoping... Any ideas?
    This really is a great piece of work coming together here. Hats off to those involved.

    As it happens I have a Tandy 1400FD outside which has 768K RAM from the factory, so I guess it used a similar trick (V20 CPU). I'd be very interested to get a copy of this Checkit3 utility you mention if possible.

    I think on the 1400 the idea for the extra RAM was disk cache (especially since it was floppy based). But as yet I've not been able to find really anything about it at all (let alone a driver).

    Leave a comment:


  • ibmapc
    replied
    Originally posted by Chuck(G) View Post
    Here are the GAL16V8 JEDEC, EQN and LOG files for anyone who wants to duplicate this. Since you'll be putting a 20-pin DIP iinto a 16-pin socket, you'll need to connect pins 8 and 10 (it's okay to include pin 9 if that makes the job easier) on the 20 pin DIP or, if you use a stacked socket, the socket. Just plug the GAL in so that pin 1 on the GAL matches pin 1 of U44 on the 5160 planar. Stick in 4 banks of 41256s and you're good to go.
    Also, I'd be willing to make the adapter socket. I still have three un modified low profile 20 pin sockets on hand. I like the low profile type because the pins are a little more substantilal than the full hieght type, and they have a shoulder that stays above the socket that it is plugged into which is were the jumper is installed.

    I'd be willing to provide one free of charge, including shipping, to anyone willing to help with the software side. Just PM me.

    Leave a comment:

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