[usb] ROM example with working string descriptors?

[Evan Jones <ejones@uwaterloo.ca>]

Hello,

We are using the OpenCores USB1.1 Function controller and are 
attempting to get our device working under Windows. Using libusb (the 
user space USB library) we have been able to get our device working 
under both Linux and Mac OS X. We want to get the string descriptors 
working to rule out possible causes of errors. Can someone post an 
example ROM that has string descriptors which are KNOWN to work 
correctly? Including the Unicode encoding? We are having problems 
getting it to work correctly, and are wondering if it is because we are 
setting up the ROM incorrectly.

We have been doing some debugging using the "USB Compliance Tool" which 
can print out the bytes read from the string descriptor. Each time we 
read the string descriptors it seems like we are getting different 
values, which is very strange. Sometimes it appears to give us the 
value in the ROM, other times it appears to be reading from nearly 
random points in the ROM. I'm trying to figure out why my program to 
dump the string descriptor under Linux isn't working, since the device 
seems to work more reliably with Linux.

The results that we are getting back are very strange. We attempted to 
create our own string descriptor, but eventually just uncommented the 
code that exists in CVS. We have a few questions about these defines, 
from usb_defines.v:

`define ROM_SIZE0       7'd018  // Device Descriptor Length
`define ROM_SIZE1       7'd053  // Configuration Descriptor Length
`define ROM_SIZE2A      7'd004  // Language ID Descriptor Start Length
`define ROM_SIZE2B      7'd010  // String Descriptor Length
`define ROM_SIZE2C      7'd010  // for future use
`define ROM_SIZE2D      7'd010  // for future use

`define ROM_START0      7'h00   // Device Descriptor Start Address
`define ROM_START1      7'h12   // Configuration Descriptor Start 
Address
`define ROM_START2A     7'h47   // Language ID Descriptor Start Address
`define ROM_START2B     7'h50   // String Descriptor Start Address
`define ROM_START2C     7'h60   // for future use
`define ROM_START2D     7'h70   // for future use


What is "Language ID Descriptor Start Length"? I'm assuming that it 
should contain the language ID descriptor length? Why is it called 
"start length"?

We set the Language ID Descriptor Start Address to the ROM address of 
the language ID descriptor, and the String Descriptor Start Address to 
the address of the first "real" string. Is this correct? Is that first 
"real" string the String Index 1?


Thank you for any assistance you can provide,

Evan Jones

--
Evan Jones: http://www.eng.uwaterloo.ca/~ejones/
"Computers are useless. They can only give answers" - Pablo Picasso

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