USB stream .Read() blocks for 1,5ms, even if ReadTimeout = 0

Archive
1

Hi,

I’ve noted that on the FEZ Panda, looking for “new data” on a stream will consistently take 1,5ms if no data is available.

When data is available, that increases just a bit to 1,65ms.
The stream is set up with ReadTimeout = 0

Any idea why this polling is taking “so long” if no data is available?
PS: sending data is quite faster, sending 60 bytes is taking around 0,6ms.

Cheers
mark

2

USB packets come every 1ms

3

I see.
So this wouldn’t be any faster on a ChipworkX module - or?

4

It wouldn’t be faster on a 3Ghz processor :slight_smile:

5

There might be room for some improvement. We will look into it fo next releases.

6

Where is the data coming from? PC? You may be able to speed up the sending to the device - i.e. avoid missing too many 1mS slots - by changing the way you do this. Depends on the code and who/what’s sending it.

7

I’m sending the data from the PC (Mac 10.6).

I don’t really have to send much data back and forth - I just have to poll the FEZ, if the PC sent it a command to adjust some parameter.

I am poling if commands where sent from the PC every 40ms (that makes sense in my app!) - no matter if a command was received or not, read will take 1,5ms. That’s quite a lot :slight_smile:

Mike/Gus: it would be great if you could look into this. Some simple means to ask if data is available would be great. Something that returns fast - and helps deciding if a Read() should be done or not.

PS: do you have a bug-tracking / feature request database?

8

We keep track of them internally.