30 Mar
2015
30 Mar
'15
8:52 p.m.
That's a very interesting project. Do you have plans to make this
thing available in some form once the bugs are out?
It's high time someone collated all the 'new hardware' projects out
there - this, Vince's Omnibus memory boards, the widget drive
replacements for Lisa, Guy Sotomayor's stuff, all these things -
should be a one-stop shop where info on all this stuff is held. Rich
Alderson, I know you guys have done work towards plug-compatible
pdp-10 memory & disk replacements, do you think that could ever be
shared? I'd love to see a Massbus connector with a CF or SD card
slot... :-)
Maybe I'll have to take up the job of collating these projects :-)
On Tue, Mar 31, 2015 at 4:41 PM, Johnny Billquist <bqt at update.uu.se> wrote:
On 2015-03-31 01:57, Paul Koning wrote:
Right, right and right. Except I don't know if the servo mechanism
necessarily is marginal. The RL drives are "funny" in that there aren't
even
any absolute seeks. When you seek on those drives you simply tell it "seek n
tracks in or out". The value of "n" is something you need to calculate
based
on what your current track is, and what track you want to get to. And when
the seek is done, you repeat if you detect that you are not on the right
track. The drive itself have absolutely no checking if it got to the right
track or not, since it don't even know what the "right" track is.
And a switch of head select does an implicit seek to whatever track is
closest to the other heads, which means a head switch can cause the drive to
move to a different track. So you always need to do a seek cycle after a
head switch.
While disks would be formatted with the tracks on both side of the platter
aligned, there is no guarantee that the heads in the drive are actually
perfectly aligned, which is why you get the head movement on head switch.
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
--
http://www.corestore.org
'No greater love hath a man than he lay down his life for his brother.
Not for millions, not for glory, not for fame.
For one person, in the dark, where no one will ever know or see.'
On Mar 30, 2015, at 7:50 PM, Christopher Parish
<christopher.parish at parishcomputers.com> wrote:
...
Second, I've noticed that the drive seems to mis-seek on occasion. I
command the drive to walk forward or back a single track, and the heads move
but sometimes land on the same starting track. This results in duplicate
data for the next 10kB or so, and is heavily pack dependent. Some packs
don't exhibit it, others do. I imagine this is related to the drive/pack
runout condition described in the manual. Until I figure out more, my plan
is to add additional verification to the incoming data, checking the track
it landed on and re-commanding the difference if necessary.
As I recall, RL01/02 have embedded servo (one of the first DEC drives to
do so). That would suggest you have a marginal servo mechanism. As for
wrong data, isn?t there a track (cylinder) number in the headers? I would
expect there to be one, so a wrong seek should be detectable.