can't download Oceanic VT3 on linux

[Linus Torvalds]

On Tue, Mar 11, 2014 at 6:27 AM, Jef Driesen <jef at libdivecomputer.org> wrote:
>
> I wonder if this is another case where the tcdrain() function isn't waiting
> properly until all bytes have been send out.

Assuming it is ftdi, we should have at least *tried* to do it since
3.8, but I really won't guarantee that it works. I'm assuming Hamish
has something newer than that, but who knows.. As usual, I think
Debian "stable" (also known as "bat shit crazy") is some ancient 3.2
kernel still, but all other distros should be much more up-to-date.

> We had a similar problem with Suunto devices before.

As you know (but perhaps others don't) this isn't a Suunto problem per
se -  the actual *real* legacy serial cable should work fine, because
on a real UART we generally have an easy way to check whether the send
buffer has actually flushed out.

But the USB people originally (consciously) decided to not make USB ->
serial be a standard, because their argument was that USB should
replace serial lines, and USB serial dongles were thus "invalid".
Morons with an agenda. As a result, there is no actual standard USB
serial conversion model, and every single USB serial chip is a "hack"
pretty much by definition.

And with simplex being *so* unusual, it doesn't get a lot of attention
and testing, and since it's not some generic standard, it's always
per-dongle-chip-driver.

> I have been looking at the kernel history for the ftdi usb-serial driver,
> and there have been some changes related to waiting until the TX buffer is
> empty, so there could be something there as well. Which kernel version do
> you have (uname -a)?

There have been interface changes, but I don't think the functionality
should have changed since 3.8 (and before that, we had no "wait for
the dongle buffer" code at all for ftdi).

That said, see above about lack of test coverage. Maybe the interface
changes broke something by mistake. And maybe it didn't work reliably
to begin with ;)

So yeah, kernel version would be interesting, but no guarantees even
then. Except for the guarantee that pre-3.8 it certainly didn't wait
for the ftdi dongle to drain.

              Linus