[BRLTTY] bc640: Some debug info

[Mario Lang]

Dave Mielke <dave at mielke.cc> writes:

>>Yes, for now, thats all that is necessary.  The Linux hiddev
>>interface has a bunch of ioctls as well (all defined in linux/hiddev.h).
>>They can be used to get "reports" and do other things, but
>>reading incoming events is as simple as reading from the device.
>
> Do you know what writing to a hiddev is suposed to do?

No.  I wasn't brave enough to try this yet, since the last
display I had for driver hacking (the Trio) died when I
wrote a slightly malformed packet to it...

> Can you, for example, just write a regular byte stream to it? If so,
> then I can tell you how to do a regular Alva write and we can see if
> that works.

If you tell me which stream, I can try.  I havent groked the
hiddev interface yet though...

> Is /dev/usb/hiddev0 a device in its own right or is it a symlink to somewhere 
> else?

Its a special device file. Quoting Documentation/usb/hiddev.txt
from the linux kernel tree:
"The hiddev interface is a char interface using the normal USB major,
with the minor numbers starting at 96 and finishing at 111."

udev automatically creates these device file if a HID compatible
USB device gets connected.

> If the device is found via searching usbfs, do you know how to then translate 
> that to the right hiddev device to open or can the usbfs device be opened and 
> read?

hiddev and plain usb devices are on a different layer in the kernel.
If we were to use usb devices directly, we would need to
impelemtn HID ourselves...  There is a libhid which can be
used to do HID IO from userspace, but I tried it yesterday
but it is buggy.  It managed to find the correct device via vendor/product
ID, but when trying to retrieve the HID descriptor it fails.  This bug
seems to be common, since I found some postings about it on the net.
So for now, I think we are better of using the linux hiddev interface.

>>Key group 1: The thumb keys.  The device has 5 thumb keys, numbers 0 to 4 from
>>left to right.
>
> All the same size and equally spaced?

Not quite, but mostly.  I have the device at home, can
examine this in detail today evening.

>>Key group 3: These keys are located below the display line, on
>>top of the device.  There are 8 of those keys, in the middle
>>you have "cursor keys" with up/down, left/right, and one button
>>in the middle.  On the sides, you have two additional keys.
>>Below are the keycodes drawn in the same layout:
>
> Are these keys below the routing keys or above them?

Below.

> Do there seem to be any limitations regarding which keys can be pressed 
> together?

I havent tried any key combinations yet.

-- 
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