can't download Oceanic VT3 on linux

[Linus Torvalds]

On Tue, Mar 11, 2014 at 5:20 PM, Hamish Moffatt <hamish at cloud.net.au> wrote:
>
> Here's a log from Windows. There appears to be a whole lot less timing
> precision so it's a bit hard to compare, other than noting the absence of
> NAKs from the VT3.

Hmm. The windows log is for 0.5.0-devel, with the Linux one being
0.4.2. But I assume there are no big libdivecomputer changes.

> [0.156] INFO: Write: size=2, data=8400
> [0.156] INFO: Read: size=1, data=5A
> [0.156] INFO: Read: size=17, data=4F43452056543320523244203531324BBF
> [0.172] dc_device_dump
> [0.172] INFO: Write: size=4, data=B1000000
> [0.187] INFO: Read: size=1, data=5A

So the Linux dump sometimes got A5 instead of 5A.

But the *timing* is very vert different. Here's Linux getting the right data:

  [0.104540] INFO: Write: size=2, data=8400
  [0.104551] INFO: Read: size=1, data=5A

and here's the same thing with the wrong data:

  [0.109560] INFO: Sleep: value=1
  [0.110624] INFO: Write: size=4, data=B1000000
  [0.110634] INFO: Read: size=1, data=A5

Note how it did a two-byte write, and then immediately a read within
10 microseconds.

Which is a bit odd. Jef, shouldn't the sleep be *after* the write, and
before the read? If there are any duplex issues, the "read -> write"
turnaround isn't the problem (because by the time the read returns, we
certainly know the data had been fully sent from the other side), but
the "write -> read" turnaround might be problematic if the reader gets
confused by DSR coming on while it's still receiving.

                 Linus