CODEWITHSUNDEEP
android
user387184
user387184

Reputation: 11053

best way to read from UsbDeviceConnection in USB host mode

To read data from an opened USB connection one uses UsbDeviceConnection bulkTransfer method.

I have the situation that after sending a request the routine should read all incoming data, which can be just 8 bytes or even 300+ bytes.

The problem is that bulkTransfer does not read all the bytes for some reason - it just returns with some bytes while there could be more to come.

Is it better to write a loop around bulkTransfer until there is no more data, or increase the timeout, or possibly there is another approach.

What would be the best way to handle this?

I tried the loop approach and I am surprised that it only reads about 10-20 bytes each time with a timeout of even 1second. I am sure there is more data already available, don't know why it does not read more at a time.

Does it matter which buffersize one uses - many examples have 4096 but how does changing this influence the reading of data?

Many thanks

Upvotes: 1

Views: 1935

Answers (1)

usethe4ce
usethe4ce

Reputation: 23819

If the device sends 10 bytes at a time and does so repeatedly to finish the 300+ bytes, you still only get these 10-byte chunks each time you read with bulk transfer.

In other words, the method does not wait to fill up your buffer. It returns as soon as there is something. So if you really want to collect the entire 300+ byte response, you do need to loop.

Upvotes: 2

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