USB HID for Power Devices
Posted: Fri Feb 28, 2020 6:38 pm
Recently I discovered the USB Composite library and have a project in mind where I want to use it. I am powering a single board computer from a battery. What I would like to do is use the USB HID for Power Devices to provide the state of the battery (which is sampled by a BluePill) to Windows. If it's then possible to have Windows display the battery state in the taskbar like for a laptop that would be great. If not then I would attempt to write some small program in C# to do this. But first I need to get the connection going. I worked through the examples (for keyboard and mouse) provided and also tried to make sense of the documents provided at USB.org.
My progress so far is slow and I was wondering if anybody has done something similar and has some examples to share?
What I have managed so far is to have Windows detect my BluePill as a "HID UPS Battery" by using the USBHID class and creating a simple ReportDescriptor:
Then I created a report structure and a HIDPower class that derives from HIDReporter (similar to the implementation of the HIDMouse). Next I tried to send a report the same way that the mouse examples send reports, by filling the report and using
I have a small application which can monitor batteries connected to my computer which kind of shows that there is now an extra battery but all the fields seems to be undefined. So my concern is that I can't really use sendReport() when sending Feature items, could this be? Is there maybe a different mechanism to send feature item data?
Not sure if it's relevant but in the HID v1.11 documentation they also mention "Only Input reports are sent via the Interrupt In pipe. Feature and Output reports must be initiated by the host via the Control pipe or an optional Interrupt Out pipe."
If anybody has some ideas or suggestions that would be great?
My progress so far is slow and I was wondering if anybody has done something similar and has some examples to share?
What I have managed so far is to have Windows detect my BluePill as a "HID UPS Battery" by using the USBHID class and creating a simple ReportDescriptor:
Code: Select all
#define HID_POWER_DEVICE_REPORT_DESCRIPTOR \
0x05, 0x84, /* USAGE_PAGE (Power Device)*/ \
0x09, 0x04, /* USAGE (UPS)*/ \
0xa1, 0x01, /* COLLECTION (Application)*/ \
0x09, 0x1e, /* USAGE (Flow)*/ \
0xa1, 0x02, /* COLLECTION (Logical)*/ \
0x85, 0x01, /* REPORT_ID (1)*/ \
0x09, 0x1f, /* USAGE (FlowID)*/ \
0x75, 0x04, /* REPORT_SIZE (4)*/ \
0x95, 0x01, /* REPORT_COUNT (1)*/ \
0x15, 0x00, /* LOGICAL_MINIMUM (0)*/ \
0x25, 0x0f, /* LOGICAL_MAXIMUM (15)*/ \
0xb1, 0x03, /* FEATURE (Cnst,Var,Abs)*/ \
0x75, 0x04, /* REPORT_SIZE (4)*/ \
0x95, 0x01, /* REPORT_COUNT (1)*/ \
0xb1, 0x03, /* FEATURE (Cnst,Var,Abs)*/ \
0x09, 0x01, /* USAGE (iName)*/ \
0x75, 0x08, /* REPORT_SIZE (8)*/ \
0x95, 0x01, /* REPORT_COUNT (1)*/ \
0x15, 0x00, /* LOGICAL_MINIMUM (0)*/ \
0x26, 0xff, 0x00, /* LOGICAL_MAXIMUM (255)*/ \
0xb1, 0x03, /* FEATURE (Cnst,Var,Abs)*/ \
0x09, 0x40, /* USAGE (ConfigVoltage)*/ \
0x75, 0x08, /* REPORT_SIZE (8)*/ \
0x95, 0x01, /* REPORT_COUNT (1)*/ \
0x67, 0x21, 0xd1, 0xf0, 0x00, /* UNIT (SI Lin:Volts)*/ \
0x55, 0x07, /* UNIT_EXPONENT (7)*/ \
0x15, 0x00, /* LOGICAL_MINIMUM (0)*/ \
0x26, 0xfa, 0x00, /* LOGICAL_MAXIMUM (250)*/ \
0xb1, 0x03, /* FEATURE (Cnst,Var,Abs)*/ \
0x09, 0x42, /* USAGE (ConfigFrequency)*/ \
0x75, 0x08, /* REPORT_SIZE (8)*/ \
0x95, 0x01, /* REPORT_COUNT (1)*/ \
0x66, 0x01, 0xf0, /* UNIT (SI Lin:Hertz)*/ \
0x55, 0x00, /* UNIT_EXPONENT (0)*/ \
0x15, 0x00, /* LOGICAL_MINIMUM (0)*/ \
0x25, 0x3c, /* LOGICAL_MAXIMUM (60)*/ \
0xb1, 0x03, /* FEATURE (Cnst,Var,Abs)*/ \
0x65, 0x00, /* UNIT (None)*/ \
0xc0, /* END_COLLECTION*/ \
0xc0 /* END_COLLECTION*/ Code: Select all
sendReport();Not sure if it's relevant but in the HID v1.11 documentation they also mention "Only Input reports are sent via the Interrupt In pipe. Feature and Output reports must be initiated by the host via the Control pipe or an optional Interrupt Out pipe."
If anybody has some ideas or suggestions that would be great?