XF551 Bugs

[+Larry]

Another thread got me thinking about this. I've heard reference to bugs in the XF551 rom quite a few times. But AFAIK, I've never actually run across one. Maybe the density switching bug?

 

I do have one "non-bug" to report -- in my experience, the XF551 (1772-02-02) has the best data separation of any Atari drive I've ever used. I've used them to read disks that my 1050's would not touch. Indus was quite good, also.

 

But anyway, if you have heard of or know of actual XF bugs, how are they manifested, and can they be reproduced?

 

-Larry

 

 

[+kheller2]

I'm aware of:

1. Density Detection issues (only switches density when reading sector 1)

2. Possible to write data to disk before drive is up to speed (not confirmed)

3. Silkscreen issues where components are labeled twice and differently depending on which side of the board you look at.

4. Two different motherboards (very slight changes)

Edited July 20, 2016 by kheller2

[Tempest]

I do have one "non-bug" to report -- in my experience, the XF551 (1772-02-02) has the best data separation of any Atari drive I've ever used. I've used them to read disks that my 1050's would not touch. Indus was quite good, also.

 

I have to agree. When I sold off all my Atari 8-bit hardware I kept my XF551 because it worked the best on my old disks (too bad it doesn't match my 1200XL).

[+Larry]

 

I have to agree. When I sold off all my Atari 8-bit hardware I kept my XF551 because it worked the best on my old disks (too bad it doesn't match my 1200XL).

 

Go for that spray paint!

[GoodByteXL]

I'm aware of:

1. Density Detection issues (only switches density when reading sector 1)

2. Possible to write data to disk before drive is up to speed (not confirmed)

3. Silkscreen issues where components are labeled twice and differently depending on which side of the board you look at.

4. Two different motherboards (very slight changes)

 

And even more when using other software than DOS 2.x with it. Actually, I shelved it for approx. 10 years because of that and had it the fixed later on with a new OS.

[1050]

I'm aware of:

1. Density Detection issues (only switches density when reading sector 1)

Not even then is my experience with it, not even with a BFH will it boot a DD disk

cold system wide power up.

Heaven help you if it's a DSDD with DOS.SYS on the 'back' side too.

Not even the Hyper can do this much for me here. I suspect it might be the

BB running interference though, I've not done enough testing or at the

very least I left the testing session a bit early perhaps? I would welcome

any Hyper users to make such a disk with DOS.SYS on the back side using

MyDOS and give that a proper cold system wide power up test run.

 

When this drive can switch densities it's because the DOS was written to do

that for the drive. A plain jane untalented DOS like MyDOS can not and

will not do this much automatically. One can make it so manually

however. And after booting some other disk first. That's almost

cheating though, or am I being too strict here?

 

An expected rebuttal will be that sector one is single density and there is

the real issue. Doubtful that is true on a DD disk even if it is a shortened

sector as must be the case since Atari's boot code is ONLY capable of

loading in 128 bytes of code per sector.

 

While it is possible that individual sectors in a track might be laid down

with different densities, I'm doubtful that the 1772 FDC is capable of such

talents. I'm thinking that it and the 2793 only do track at once formatting,

where every sector in a track is the same density, especially in the

respective Atari written drive OS we are using.

I can be wrong of course.

 

No other bugs come to mind, but this one is pretty bad all by itself.

Can't use it for D1: here.

[+kheller2]

1050: I'm not sure I understand the issues you are experiencing. Of course the XF can't switch densities if the DOS isn't capable of doing so. I'm also pretty certain you can format a DSDD disk, load it up, and then lay down a DOS.SYS on the backside -- but that depends on the DOS if its capable of being strapped/linked beyond the first 720 sectors. Also, the 279x in the 1050 can do different densities per sector -- this is a bug in the 1050 Duplicator where sectors 1-3 are SD and the rest is DD. DD formats usually mirror the lower 128 bytes to the upper 256 bytes for sectors 1-3, as I recall. I've used the XF551 as D1 for several years.

 

Larry, Tempest: The FDC 1772 has a newer "digital" data separator (vs the old internal DS in the 279x) and does away with external analog components needed in prior chips. Also keep in mind the XF is using a newer drive mech as well.

[sup8pdct]

One early bug was SIO timing was out for PAL machines. The updated rom works with both NTSC and PAL.

 

Re data separator, Indus and 1050 use same family chip. Data separator uses adjustable external components. Need a scope to adjust them properly tho.

James

Edited July 20, 2016 by sup8pdct

[Bryan]

Just remembering.... doesn't the XF have to be power cycled if it cannot complete a read command. It seems to me like powering the computer on and off won't bring it back (that is, new commands can't abort the perpetual previous read attempt).

[Rybags]

Power cycling the computer doesn't sound like making sense. A drive could only detect that by sensing the +5V/Ready dropping out then coming back - not sure many perpipherals on A8 bother with that.

Power cycle would initiate a bunch of new /Command sequences but you can do that plenty of other ways.

 

Did the XF551 use bit-banging with delay loop methods or was external timing used to generate the bit rates required?

Edited July 21, 2016 by Rybags

[sup8pdct]

Timed loop with cycle counting. Lots of NOP's used. The 8040 or 8050 only has 256 bytes of ram. To buffer a DD sector, one byte is stored in timer register leaving one byte free for a bit counter to bit bang 8 bits.

 

James

[ijor]

Power cycling the computer doesn't sound like making sense. A drive could only detect that by sensing the +5V/Ready dropping out then coming back - not sure many perpipherals on A8 bother with that.

 

Happy drives use it in some cases. When you run the Happy backuper, for instance, there is no software way to put back the drive in normal mode. Either power cycle the drive, or power cycle the computer. The drive will detect it and reset itself.