Android bulkTransfer return -1 when read data but there is really some data in the buffer

Question

I write a app in galaxy tab p7300 to communicate with a key (scsi device) via otg cable. I can read data first time with bulkTransfer(),but can not the next time . Then I u

Answer 1

Its too late to post a solution , but in case in future someone needs help about it can get an answer from here.

I faced the same issue. I was using Android (Samsung galaxy s3) as usb host device. I figured out about the read endpoint and write endpoint not trasferring data using USB BulkTransfer. I tried to switch the endpoints for host mode case, it recognized and successfully write/read the data.

 mReadEndpoint = mDataInterface.getEndpoint(0);// tweaking endpoints // 1 was for read and 0 was for write
 mWriteEndpoint = mDataInterface.getEndpoint(1);

P.S there is an application available for android named "USB device info". It helped me a lot in understanding interfaces and endpoints of my usb device.

Answer 2

When using the USB Bulk transfer, here is a list of things to check when transaction fails

a) Verify the direction of the endpoint you have passed the bulkTransfer function

b) ensure that the buffer has sufficient length to store incoming data

c) The length field is perhaps the most important. If you know the exact size of the response, use it.

d) The Timeout parameter. If you send a query to the device and do not provide enough timeout when listening to the response, the bulkTransfer can return -1.

It looks like the timeout is affecting behavior in your Case. My suggestion is to use the exact number of bytes in the length fields for each response, and use a longer timeout (like 1000) so you give enough time for the bulk request to complete.