Hello,
I am using USB-UART optical serial converter [1], which is based on
MCP2200.
It is connected to my RaspberryPi and the other side is connected to my
remeha
gas boiller.
My problems starts with this commit:
commit a81cf9799ad7299b03a4dff020d9685f9ac5f3e0
Author: Oliver Neukum <oneukum@xxxxxxxx>
Date: Wed Feb 10 10:39:49 2016 +0100
cdc-acm: implement put_char() and flush_chars()
This should cut down latencies and waste if the tty layer writes
single bytes.
Signed-off-by: Oliver Neukum >oneukum@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
I was trying to resolve the problem with Oliver but we don't get any
conclusion
for 5 months, so I am now sending this to mail list and cdc_acm authors.
I am using simple request-response protocol to obtain the boiller
parameters
in constant intervals.
A simple one transaction is:
1. opening the /dev/ttyACM0
2. sending the following 10-bytes request to the device:
unsigned char req[] = {0x02, 0xfe, 0x01, 0x05, 0x08, 0x02, 0x01,
0x69, 0xab, 0x03};
3. reading response (frame of 74 bytes length).
4. closing the descriptor
I am doing this transaction with 5 seconds intervals.
Before the bad commit everything was working correctly: I've got a
requests and
a responses in a timely manner.
After the bad commit more time I am using the kernel module, more
problems I have.
The graph [2] is showing the problem.
As you can see after module load all seems fine but after about 30
minutes I've got
a plenty of EAGAINs when doing read()'s and trying to read back the
data.
When I rmmod and insmod the cdc_acm module again, then the situation is
starting
over again: running ok shortly after load, and more time it is running,
more EAGAINs
I have when calling read().
As a bonus I can see the problem on the device itself:
The device is configured as you can see here on this screen [3].
It has two transmision LEDs: TX and RX. Blink duration is set for 100ms.
This is a recording before the bad commit when all is working fine: [4]
And this is with the bad commit: [5]
As you can see the TX led is blinking wrongly long (indicating
transmission?)
and I have problems doing read() calls (EAGAIN).
Refs:
[1] http://nicke.pe.hu/mcp2200opto/mcp2200opto.html
[2] http://skyboo.net/temp/cdcacm/grafana.png
[3] http://nicke.pe.hu/mcp2200opto/config.png
[4] http://skyboo.net/temp/cdcacm/OK_before.mp4
[5] http://skyboo.net/temp/cdcacm/BAD_after.mp4
regards,
--
Mariusz Białończyk | xmpp/e-mail: manio@xxxxxxxxxx
https://skyboo.net | https://github.com/manio
