Strange problems with CH340G (uchcom)

[Hans Petter Selasky]

On 04/20/15 21:48, Bernd Walter wrote:
> I tried to flash an ESP8266 with the onboard CH340.
> The same board works fine when I use a CP2102 instead of the CH340.
> Flashing requires a python tool, which sends a SLIP encoded request
> and expects a SLIP encoded response with 115200 at 8n1.
> The read function however times out receiving the response without
> getting a single byte, even if I add a high delay between sending and
> reading.
> The strange thing is that I can see a valid response on a scope just
> a few µs after the request completes, while the receiver don't even
> see the first byte.
> If however I physically loopback the CH340 it receives it's own request
> just fine.
> Two CH340 xconnected work fine too.
> Same when I xconnect a CH340 and a CP2102.
> Now I'm completely out of ideas, why the python tool has problems
> to see the response data with the CH340.
>

Try using:

usbdump -i usbusX -f Y -vvv -s 65536

And see if the reply is seen by the USB ... maybe it is a timing issue 
like one character at a time instead of a word.

--HPS