Sending data packets to USB bulk endpoint

[Wall, Stephen]

I posted this on the FreeBSD Drivers forum, got no response, so I'm trying here.

I am working on a driver to support a Silicon Labs I2S to USB bridge. Besides the audio portion, the chip supports a bulk endpoint which uses a documented packet format to read & control 16 GPIO pins, and to pass messages to & from an I2C bus. I have not previously worked with USB, or FreeBSD drivers. I'm been handed a partially complete codebase - the audio stream works - and I'm trying to get the GPIO controls working. My intent is to use ioctl() calls to read and set the pins.

Creating an entry in /dev and the associated character device structure for the GPIO control is pretty straightforward. Where I'm getting stuck is trying to figure out how to get the messages I am creating in the driver down to the bulk endpoint - the USB driver code is a bit overwhelming to a newcomer, and I can't seem to find a function that fits "send this block of data to this endpoint". The only way I've seen for interacting with bulk endpoints is to write a driver based on usb_fifo_methods rather than cdevsw (per "FreeBSD Device Drivers", chapter 15), which does not seem to fit what I'm trying to do.

I would appreciate any pointers experienced driver developers could give me to get where I'm trying to go with this - either the name of the function I'm looking for, or some other was to get that functionality.

Thanks.

- Steve

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Stephen Wall
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