someone who has the 4mb ram card working properly

[hpmin48gx]

Hello friends of the forum, sorry if I return to this topic but I want to be sure of the operation of the ram that I made, so I would like to send it to someone who has that ram and who can tell me if it works correctly, preferably in the US, I suppose there is someone who have this ram

[Christoph Giesselink]

No, it will not work properly.

There's a bug in the firmware for 4MB cards and every time you switch on the calculator you will get a Card Error. You can use the 4MB carld less one 128KB page affected by the bug.

Christoph

[hpmin48gx]

Well, what I have tried does not have that error, that is why I would like to send one, rather that invalid card error according to the card manual appears when you block the write mode

[Christoph Giesselink]

(02-04-2023 05:29 PM)hpmin48gx Wrote:  Well, what I have tried does not have that error, that is why I would like to send one, rather that invalid card error according to the card manual appears when you block the write mode

Many years ago I tried to fix the card problem with a ROM patch in Emu48.

The first problem, when you try to access the last bank in the 4MB RAM, the chip enable signal for the RAM get lost. This is an issue caused by a special behavior of the bank switcher hardware. This can be fixed by a ROM patch.

2nd, after fixing the bank switcher problem, I still got errors. The 4MB card is divided into 32 bank of 128KB. For each of these banks the OS reserve some in the calculator RAM in a table for administrative purpose. I was very astonished when I recognized that HP developers made a calculation mistake. The reserved table space had not room for 32 entries, only for 31! So the last entry in the table shares the memory with other intermediate data. So when the intermediate data was written, the administrative bank data for the last bank get lost. The corrupt data is then detected when you switch on the calculator. This cannot be fixed by an easy ROM patch.

So there's definitely no chance to get a 4MB RAM card properly working in a HP48GX.

[hpmin48gx]

(02-05-2023 01:35 PM)Christoph Giesselink Wrote:  

(02-04-2023 05:29 PM)hpmin48gx Wrote:  Well, what I have tried does not have that error, that is why I would like to send one, rather that invalid card error according to the card manual appears when you block the write mode

Many years ago I tried to fix the card problem with a ROM patch in Emu48.

The first problem, when you try to access the last bank in the 4MB RAM, the chip enable signal for the RAM get lost. This is an issue caused by a special behavior of the bank switcher hardware. This can be fixed by a ROM patch.

2nd, after fixing the bank switcher problem, I still got errors. The 4MB card is divided into 32 bank of 128KB. For each of these banks the OS reserve some in the calculator RAM in a table for administrative purpose. I was very astonished when I recognized that HP developers made a calculation mistake. The reserved table space had not room for 32 entries, only for 31! So the last entry in the table shares the memory with other intermediate data. So when the intermediate data was written, the administrative bank data for the last bank get lost. The corrupt data is then detected when you switch on the calculator. This cannot be fixed by an easy ROM patch.

So there's definitely no chance to get a 4MB RAM card properly working in a HP48GX.

Hello Sr. Christoph, the only thing I want is to know if the copy of the card works the same, whether it's good or bad, I could send you one if you allow it.
[/quote]

[hpmin48gx]

Hello Sr. Christoph, the only thing I want is to know if the copy of the card works the same, whether it's good or bad, I could send you one if you allow it.

[Eric Rechlin]

It's true that a conventional 4 MB card won't ever work perfectly. However, there have been workarounds. At least one vendor came out with a 4 MB card with a physical switch that switched out the top bank(s) so the card would never have the full 32 ports visible at once. I believe it only had 30 ports at a time, with ports 29 and 30 switching with 31 and 32 if you wanted to use the last little bit of space. That allowed the card to never produce errors.

[hpmin48gx]

That's exactly what the switch does, the other switch only activates and deactivates writing and when deactivating writing the invalid card message appears until it is activated again

[Kiwi]

Indeed, Eric is right. See also my answer in your other thread here

[Christoph Giesselink]

(02-05-2023 02:08 PM)hpmin48gx Wrote:  Hello Sr. Christoph, the only thing I want is to know if the copy of the card works the same, whether it's good or bad, I could send you one if you allow it.

TNX for the offer, but the maximum real card I have is a 1MB card. The knowledge I have is the result of my work on Emu48. The original Emu48 version v1.0 from Sebastien Carlier haven't reported an error in connection with a 4MB RAM card when virtually switching on the HP48GX.