@zeilemaker54: I think there might be an error in the DPB (for 0xFB) of the 8250, FS-A1GT, HB-F700-p-alt and HBD-F1 (haven't checked them all by the way).

As far as i can tell, FIRREC (the first sector where the data area begins) should be 12 and not 10.

0 bootsector
1 fat
2 fat
3 fat (second)
4 fat (second)
5 directory (112 entries / 16 = 7 sectors)
12 data area

Correct? Is this an error in the sources, of perhaps a bug in the roms?

I remember this, when I dissasembled one diskrom

IIRC at bootsector is 8 or 10, but as the two first element at fat is the ID media, so if at boot just set 12 that means that the two first clusters are not usable.

so, at boot sector the location of the first clustor is set at the end of the root directory, so the two first clusters (unusable) fall at the end of the root directoty and the first usable FAT element, fall at sector 12 allowing the use of all the disk space.

Anyway the diskrom doesn't read the boot sector looking for the format and the location of the data...

It uses internal format tables in ROM....

To identify the disk format, it only reads the sector 1, looking for the ID media....

But it reads the boot sector looking for the boot-code when you turn on the msx. Then it is unused (atleast in basic)

msxrestarter: ah, that would be great! The best thing to do that would really help is this:
- get saverom.com from http://bifi.msxnet.org/msxnet/utils/saverom.html
- put it with MSX-DOS on a single sided floppy (duh!
- do this:

saverom 8230-30.bin
Primary slot: 3
Secundary slot: 0
MegaROM? n
Start address: 0
End address: FFFF

and then the same for slot 3-3:

saverom 8230-33.bin
Primary slot: 3
Secundary slot: 3
MegaROM? n
Start address: 0
End address: FFFF

and then also for the 8235.

This would give us all we need to know to perfect the emulation of those machines.

We did the same on the 8245, 8250 and 8280 and there were interesting results!

On a 8245, the subROM is only visible in page 0 (slot 3-0). On the 50 and 80, the subROM is visible in all 4 pages in slot 3-0! (Now also in openMSX.)
On a 8245, the diskROM is visible in page 1 in slot 3-3 and the FDC registers are also mirrored on page 2 (as Kwik discovered, this is in (almost?) all openMSX machines with FDC). But on the 50 and 80, the FDC registers are visible in all pages!

So, I'm really curious how this is on the 30 and 35 (and also about the subROM on the 8220!). So, if you can help us here, it would really be great

What i meant was that FIRREC at sector 10 cannot be right, because it would overlap part of the directory entries.

nono as I explained before.

I was talking about Drive Parameter Blocks, not the information that is recorded in the bootsector!

And the SVI-738 also seems to have FDC registers mirrored in all pages of slot 3-1.

(DPB) I mentioned it as the "table format's definition at ROM or something" is the same data by the same reason.

If you SET "12" (5 1/4) or "14" (3 1/2) as first sector for the first cluster.... that means that the sectors 12,13,14 & 15 (5 1/4) or the 14,15,16 & 17 (3 1/2) can't be used for store files, because that match with the first and second element at FAT.

first element: ID media = &hFF9 by example
second element: <EOF> = &hFFF
(that is the first 3 bytes at fat on a normal disk)
theses are allways those values and by that reason, the first and second logical clusters (logical sector 12,13,14 & 15) or (14,15,16 & 17) are not usable.

Q: So, wasting 4 sectors on a small disk capacity????
A: Naaaaaaahhhh.... just to define the the first sector for the storage area is the sector 8 (in 5 1/4 disks), 10 (in 3 1/2) , that means that the third FAT element and the first usable will fall on the logical sector 12 or 14 respectively, and that is the first one really available.

In 3 1/2 is large the ROOT DIR (IIRC) and the number is 10 at DPB or bootsector, so jumping to the third fat elements that is usable will fall at logical sector 14...

please somebody correctme about numbers, (I just hasn't the IBM-PC book at hand.)

@Kwik: I will look into it. May be it is a bug.... But I have never seen a disk with mediaid 0FBH in the real world. It is supposed to be a 8 sectors/track disk, which is a total waste on a 3.5" or 5.25" disk. It is probably only supported, because it is defined in the PC-world (e.g. MSDOS).

Quote:

@zeilemaker54: I think there might be an error in the DPB (for 0xFB) of the 8250, FS-A1GT, HB-F700-p-alt and HBD-F1 (haven't checked them all by the way). As far as i can tell, FIRREC (the first sector where the data area begins) should be 12 and not 10. 0 bootsector 1 fat 2 fat 3 fat (second) 4 fat (second) 5 directory (112 entries / 16 = 7 sectors) 12 data area Correct? Is this an error in the sources, of perhaps a bug in the roms?

It seems that I have made a error with the creation of the source for the diskrom's of the NMS-8250 and the FS-A1GT. They have indeed the right DPB for mediaid 0FBH. But both the HB-F700 and HBD-F1 have the error in the DPB for mediaid 0FBH!!!! This means that in both cases, disks with mediaid 0FBH will not be read correctly!

Zeilemaker: do you have any idea about the phenomena I posted? (FDC register mirroring in 2 or 4 pages, e.g.)

Well, this must be a hardwaredesign issue (something to do with addressdecoding of the FDC). May be someone with MSX hardwareknowledge can comment on this. May be Hans Otten or Hans Oranje are the right persons for this issue.

Quote:

Zeilemaker: do you have any idea about the phenomena I posted? (FDC register mirroring in 2 or 4 pages, e.g.)

@Zeilemaker: So what you say is that the original rom of the HB-F700 and HBD-F1 have an error in the DPB for 0xFB?

Yep, that is what I am saying.

Quote:

@Zeilemaker: So what you say is that the original rom of the HB-F700 and HBD-F1 have an error in the DPB for 0xFB?