mConnection.requestWait() block when data length==32

[yaphone]

Hi,
I used usb-serial-for-android lib with a ch340 hardware, it recieve data from ch340, when the data length is not 32 or 32 * n, it works well, but it DOS NOT work when the data length is 32 or 32*n like "hellohellohellohellohellohellohe" (length = 32) or "hellohellohellohellohellohellohehellohellohellohellohellohellohe"(length = 64) . I debug it, found it block at mConnection.requestWait().

And I set usbSerialPort.setParameters(115200, 8, UsbSerialPort.STOPBITS_1, UsbSerialPort.PARITY_NONE);

Very strange problem, anyone can help?

Thank U very much!

[kai-morich]

Do you use SerialInputOutputManager? There it is normal that read without timeout typically blocks to fetch next data. If you use read in your main thread, you better use timeout to return the available data.

[yaphone]

I tried to set timeout like usbSerialPort.read(response, 1000), but still not work, it still can't recieve data when length==32，just cause an exception. And I also tried the example of this project, not work too. And finally I use the driver provided by original factory, it works well.

I still don't know why...

[kai-morich]

I could not reproduce this issue with my CH34x test devices, there was no problem with length=32.
As the vendor does not provide a full data sheet, it's unclear what might be wrong.

[yaphone]

Maybe, I am the only one with this problem, so I think it is not representative. You can close this problem if If you think it is necessary.

Thank you all the same~~ 💯

[cofung]

I have the same issue, it block at mConnection.requestWait(), and after close the port, it receive the data from onNewData().

[kai-morich]

now I could reproduce the issue.
please try read() with buffer size 32 instead of 8192 as used in example app.
with this size the issue was gone.

I can only speculate about the reason:

• The CH34x uses an USB packet size of 32 bytes. If less data is available the Android/Linux USB library immediately returns the available data. If a full packet is available it tries to read the next packet. With bulkTransfer I got a -1 after the timeout and the data was lost. Later send data was correctly recieved.

The issue did not occur with other device types (FTDI, Prolific, ...)

[yaphone]

THX@kai-morich

Finally I used the driver which provid by the original factory, I will try it again next time when I use ch34X chip.

THX all the same!

[kai-morich]

for SerialInputOutputManager fixed with 848d4e7

[xmutzlq]

i have the same issue, when i send "11111111111111111111111111111111111111111111112"，the "2" is not receive，then i try to send "111111111111111111111111111111111111111111111122"，data is full receive，i do not know how to resolve，can you help me？
i have set "mSerialIoManager.setReadBufferSize(46);"
dependencies {
implementation 'com.github.mik3y:usb-serial-for-android:3.3.1'
}

[kai-morich]

when using SerialInputOutputManager you do not have to set the buffer size any more, as it already sets the optimal size = 32.

[xmutzlq]

we have resolved yesterday，cause write data timeout is too short，we have increased timeout, finally it works well
thank you @kai-morich