USB Transceiver & USB Gadget driver doubts

David Brownell

2008-01-07 20:10:06 UTC

Post by Midhun A
Hi All,
I have started to write the gadget driver for i.MX21 (CSB535FS
Board). I am writing it based on the OMAP driver present in the
mainline kernel.

Are those controllers at all similar?

And I'm quite sure I've seen an i.MX peripheral controller driver
posted somewhere ... maybe a buggy one, and certainly it's not
been merged to mainline, but it may well be easier to start with
that one than write a new one.

Post by Midhun A
1. I configured the OTG of i.MX21 as a function only (and not as OTG).
On the hardware side, I dont have an OTG transceiver (I think it comes
with I2C control) but rather the normal USB tranceiver (Fairchild -
USB1T11A). Is this fine?

It's certainly a useful configuration. Just be aware that when
someone makes a fully OTG-capable version, things may need to
be shuffled around ... and make that shuffling easier.

Post by Midhun A
2. In the driver, I have just implemented the probe of UDC as of now.
I see a method for pullup disable in the OMAP driver. What is this
for? Where is this pull up used?

It's used to control enumeration. When the pullup is disabled,
the host won't detect a peripheral on that line. When it's
enabled, it will detect the peripheral. It's under software
control, since the peripheral should be invisible until it's
able to respond to the host.

Post by Midhun A
Is this specific for OMAP?

Every USB peripheral controller should offer the option to
manage the signal pullup in software. See the USB 2.0 spec;
it's a D+ pullup on everything except low speed devices,
where it's a D- pullup. In the absense of SRP, hosts detect
peripherals by seeing one of the two signal lines pulled up

So while the specific implementation of that pullup may be
specific to OMAP,

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