USB SD-card reader recognized, but not working, on 6.1

[perryh at pluto.rain.com]

Roland Smith <rsmith at xs4all.nl> wrote:
> Are you sure that the drive isn't partitioned? In other words,
> if you plug in the drive, and you give the command 'ls /dev/da0*',
> do you only get /dev/da0 or perhaps also /dev/da0s1? If it is
> partitioned, try /dev/da0s? instead.

It's an SD card, not a "drive", so I had not expected it to be
partitioned; but yes, it is:

$ ls -l /dev/da0*
crw-r-----  1 root  operator    0, 244 Feb 14 15:09 /dev/da0
crw-r-----  1 root  operator    0, 245 Feb 14 15:09 /dev/da0s1

> Second, does the user running mtools have read and write access
> to the device?

Read-only, which should be sufficient for mdir.  The card is,
deliberately, write-protected.

After reconfiguring mtools to read from /dev/da0s1, I started
getting those umass0: BBB bulk-in clear stall failed, TIMEOUT
messages again, but I can read it a sector at a time using dd:

$ dd if=/dev/da0 of=~/sd bs=1b

That's been running for something like 45 minutes now, and based on
the size of the output file it has read about a tenth of the card.

It looks as if the problem arises only when attempting to read
larger blocks.  (I haven't tried to find out how much larger.)

> Have you tried just mounting the card reader?

No, because I'd expect to panic the system if it is not in fact a
valid (and readable) FAT filesystem.  Mtools seems much safer.