Hello,
Does anyone have any pointers about where I can look up information on how the Linux USB stack (in the 2.4 kernels) initializes and assigns a new device?
The source code is the best reference, but you seem to need interpretation instead ...
> I'm doing some debugging on a USB device that we have built
using the OpenCores USB1.1 controller (http://www.opencores.org/projects/usb1_funct/), and I can't quite figure out what is going wrong. Linux reports "could not assign address: Error -75 (babble)", but I'm trying to figure out where exactly this error comes from. Is there any way that I can get MORE debugging output out of the USB stack, besides just the "USB debugging" kernel option?
In this case I'd suggest you apply a USB sniffer of some kind and see what's happening on the wire. Like a CATC.
That's a really odd error to see for a SET_ADDRESS request, suggesting a hardware level problem. You're using OHCI, and you can see from the OHCI spec that EOVERFLOW (75) is used for one specific error.
We think that the USB function controller is correct, since it has been used by others for working devices.
That doesn't mean there aren't initialization quirks that can make it misbehave, if your driver is broken or if there were problems translating that core into real circuitry. If those other devices followed a narrow "golden path" through all the options, and your work isn't ...
The first time we connect the device we seem to get this sequence of packets. I need to go back into the lab and verify my notes, but I believe this to be correct:
SETUP (host -> device address: 0 endpoint: 0) DATA0 GetDescriptor (h -> d)
That looks wrong ... Linux doesn't fetch descriptors from devices with address zero.
ACK (d - > h)
... ~ 1ms later:
SOF (h - > d) IN (h -> d addr: 0 endpoint: 0) DATA1 (d -> h) -- contains 0x0000 then the 2 bytes CRC ACK (h -> d)
That's wrong ... descriptors don't start that way. Though I could imagine a buggy function/"gadget" driver returning a broken descriptor.
- Dave
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