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HIMEMV2 or equivillent PROM

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    #31
    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.

    Comment


      #32
      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.
      Reach me: vcfblackhole _at_ protonmail dot com.

      Comment


        #33
        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.

        Comment


          #34
          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.
          Reach me: vcfblackhole _at_ protonmail dot com.

          Comment


            #35
            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?

            Comment


              #36
              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.

              Comment


                #37
                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.
                Reach me: vcfblackhole _at_ protonmail dot com.

                Comment


                  #38
                  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.
                  Current systems owned by me:
                  Vintage:IBM PC/XT submodel 087 ( 1983 ), [Kon]tiki-100 rev. C (1983), Compaq Portable I ( 1984 ), IBM PC/XT submodel 078 ( 1985 ), IBM PC/XT286 ( ~1986 ), 3x Nintendo Entertainement Systems ( 1987 ).
                  Obsolete:Commodore A500 ( ~1990 ), IBM PS/2 model 70/386 type 8570-161 ( 1991 ), Atari Lynx II ( ~1992 ), Generic Intel 486SX PC ( ~1993 ), AT/T Globalyst Pentium w/FDIV bug MB ( 1994 ), Compaq 486DX4 laptop ( ~1995 ).

                  Comment


                    #39
                    Per, the test has to be made before the first driver loads high. So it's got to be in a device driver.
                    Reach me: vcfblackhole _at_ protonmail dot com.

                    Comment


                      #40
                      you can run program files from config.sys, at least in later versions of DOS (unless I'm slightly mistaken).
                      Current systems owned by me:
                      Vintage:IBM PC/XT submodel 087 ( 1983 ), [Kon]tiki-100 rev. C (1983), Compaq Portable I ( 1984 ), IBM PC/XT submodel 078 ( 1985 ), IBM PC/XT286 ( ~1986 ), 3x Nintendo Entertainement Systems ( 1987 ).
                      Obsolete:Commodore A500 ( ~1990 ), IBM PS/2 model 70/386 type 8570-161 ( 1991 ), Atari Lynx II ( ~1992 ), Generic Intel 486SX PC ( ~1993 ), AT/T Globalyst Pentium w/FDIV bug MB ( 1994 ), Compaq 486DX4 laptop ( ~1995 ).

                      Comment


                        #41
                        Originally posted by per View Post
                        you can run program files from config.sys, at least in later versions of DOS (unless I'm slightly mistaken).
                        Yes, but they're run after device drivers have been processed, in the same way that SET statements are processed in the CONFIG.SYS file.

                        If I get a few minutes this afternoon, I'll make the driver mods, rather than waste time gumming the subject to death.
                        Reach me: vcfblackhole _at_ protonmail dot com.

                        Comment


                          #42
                          I found some time to throw together CLEARMEM.SYS (attached).

                          Invocation is easy, just put it in your CONFIG.SYS file ahead of the USE!UMBS.SYS command. It takes two arguments, both in hex. The first is the starting segment address of an area to be zeroed; the second is the hex number of paragraphs to clear. CLEARMEM releases its memory after it clears, so it doesn't occupy any space permanently.

                          So, to clear the range between D000:0 and E000:FFFF, use the following statement in CONFIG.SYS:

                          DEVICE=CLEARMEM.SYS D000 2000

                          In other words, clear 8192 (decimal) paragraphs, or 128K starting at segment D000.
                          Attached Files
                          Reach me: vcfblackhole _at_ protonmail dot com.

                          Comment


                            #43
                            That did it!!
                            Now boots everythime without the Parity Check. Thanks again Chuck.
                            And by the way, you are right, of coarse,I do need to learn assemly. I guess I've felt that it was beyond my mental abillities. Maybe you could recomend a good book? Something like Assembly X86 for old Dummies?

                            Best regards,

                            Greg

                            PS Boy o Boy, this 5155 is a real Hot Rod now!

                            Comment


                              #44
                              Reading books about machine architectures can induce coma in many people. And I'm the wrong one to recommend a tutorial--the best thing to do is to ask someone who's just learning about the subject.

                              That being said, take a look at this tutorial that you can run on your 5155. I think it's pretty cool.
                              Reach me: vcfblackhole _at_ protonmail dot com.

                              Comment


                                #45
                                I hauled out one of my XT clones and looked at the motherboard. It appears to be a Turbo 640, or a close relative, with an ERSO BIOS.

                                One thing that caught my eye was a socketed 16-pin IC just to the right (looking from the rear) of the BIOS sockets, near the edge of the PCB. It turned out to be a 82S129 PROM, which is the Signetics equivalent of the 24S10 PROM on the 5160. I suspect, but haven't verified, that the HIMEMV2 mod will work as-is on this board.

                                Here's my question to the XT clone community at large.

                                If you have a XT clone motherboard with 4 x 9 chip RAM organization that accepts 256Kb DRAMs in at least the first two ranks, do you also have a socketed 16-pin bipolar ROM on your board?

                                Since the ERSO design was the reference design for most Taiwanese XT clones, I suspect the answer will be "yes". There are later designs where the last two ranks of RAM are replaced with 4464-type chips, but they're easily recognizable, as they don't have the "block" of 36 chips arrangement.
                                Reach me: vcfblackhole _at_ protonmail dot com.

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