HID Descriptors: bLength and wDescriptorLength

Question

Hello HID experts:
USB spec says:
bLength: Numeric expression that is the total size of the HID descriptor.
wDescriptorLength: Numeric expression that is the total size of the optional descriptor.
My questions are:
(1)  What is the difference between these two? From the description, I could not see the difference.
(2)  What is "optional descriptor" ?
(3)  I saw some descriptors showing size of bLength = 1 (byte) but
size of wDescriptorLength is 2 (bytes). Why?
Thanks in advance.
Polaris
leo

Answer 1

As refered above, the newer Macbook models 5.1 requires the dkms module, but it's possible to put it working.
With a fresh installation, the synaptics driver reported to work (command: synclient) using the options presented in:
http://wiki.debian.org/MacBook#Synaptic … MacbookPro
But, didn't have tapping or two finger scrolling....
So enough introduction :-P
To have the touchpad working with all the options you need to first get a version of bcm5974-dkms:
git clone http://bitmath.org/git/bcm5974-dkms.git
Next go to $BASEDIR/bcm5974-dkms/usr/src/dkms_source_tree
where you find a bcm5974.c
The Makefile have to be modified to contain the following:
obj-m := bcm5974.o
KDIR := /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)
default:
$(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules
Run make, at this point you have a new kernel module: bcm5974.ko
It's necessary to install. To do so run as root the following script: install.sh
#!/bin/sh
install -m 644 bcm5974.ko /lib/modules/`uname -r`/kernel/drivers/input/mouse/bcm5974.ko
/sbin/depmod -a
This will replace the kernel module in the kernel tree. Next reboot.
This procedure work for me. Please give me feedback, I like to know if also works for you ;-)
Last edited by rocket (2009-03-29 14:02:57)