Diskrom mirror differences between openMSX en BlueMSX

Page 3/8
1 | 2 | | 4 | 5 | 6 | 7 | 8

By Kwik

Expert (127)

Kwik's picture

29-01-2007, 22:40

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

By Manuel

Ascended (18781)

Manuel's picture

29-01-2007, 23:47

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

By flyguille

Prophet (3028)

flyguille's picture

30-01-2007, 02:26

(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.)

By zeilemaker54

Champion (341)

zeilemaker54's picture

30-01-2007, 09:19

@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).

@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?

By Manuel

Ascended (18781)

Manuel's picture

30-01-2007, 12:57

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

By zeilemaker54

Champion (341)

zeilemaker54's picture

30-01-2007, 12:57

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!

By zeilemaker54

Champion (341)

zeilemaker54's picture

30-01-2007, 13:01

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.

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

By Kwik

Expert (127)

Kwik's picture

30-01-2007, 13:56

@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?

By zeilemaker54

Champion (341)

zeilemaker54's picture

30-01-2007, 13:58

Yep, that is what I am saying.

@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?

By msxrestarter

Master (224)

msxrestarter's picture

30-01-2007, 21:20

@manuel : got 'disk offline' problems with the 8230 and 8235. Probably worn drive belts because they're eating dust for some time now. Will get some new belts and try to fix them this weekend. I'll let you know as soon as I got them running again Smile

Page 3/8
1 | 2 | | 4 | 5 | 6 | 7 | 8