Messages in this thread | | | Date | Tue, 30 Sep 2008 01:04:26 -0400 | From | George Nychis <> | Subject | help finding entry point of USB data in the kernel, not drivers/usb/core/devio.c? |
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Hi all,
I am trying to find the entry point of USB data in the kernel. I have a USB device and I would like to find the latency between the time the data enters the kernel, and I read it in userspace. My first goal is to find where it actually enters the kernel.
The host device driver obtains a URB and reads the data from urb->buffer.
From digging around the kernel code, I had assumed the entry point for all USB data was in drivers/usb/core/devio.c::usbdev_read() ... but it seems as though that is not the case.
Right after the device is locked in this function, I added a simple printk: printk("Reading %d bytes\n", nbytes); // Line 135
Then around line 154 after it reads the usb device descriptor, I added: if(temp_desc.idVendor==0xfffe && temp_desc.idProduct==0x0002) { printk("...Data from USRP\n"); }
That gives me an idea that the data is coming from the device I am looking for.
But, it seems as though this method is only related to control information to/from the USB device? Whenever I start my application, I get about 1614 total bytes read from my first printout, and I see only one of my second printout messages. Whereas, I am reading a total of about 8MB from the USB device over the period of time. So I think I am completely missing my actual data entry point.
Additionally, lsusb generates this same exact amount 1614 total bytes of data... so it seems to be control related to me.
I'd greatly appreciate any guidance.
Thanks! George
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