On Sep 20, 2009, at 10:13 PM, Tom Isaacson wrote:
Does anyone have example code for how hid_get_item_value() can be used? I can see how the code is implemented but not what it can be used for.
Let's say you have the hex HID "path" that represents UPS.BatterySystem.Battery.Voltage, and you don't know which report contains that usage. hid_get_item_value() finds the report ID that contains that usage, and fetches the whole report using a control message. It then extracts the single value corresponding to that usage. Unfortunately, this does not handle arrays of values, or other compound types.
In the Network UPS Tools project, we found out that this is wasteful of bandwidth, especially if you only have a low-speed USB device. That project uses a precursor to this version of libhid, but the HID code is modified to cache the retrieved reports for a certain amount of time. So this example is based off of a different lineage code, and is probably harder to understand.
You would use it similarly to hid_get_input_report() (which is used in a comment in test_libhid.c), except that you would be allowing libhid to parse the report (versus getting the raw report from hid_get_input_report()).
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