Hard fault when using USB HID with no USB connection

[nedkonz]

I have an application that needs to send HID reports (joystick) when connected to a computer, but still has to work when not connected to a computer.

My Pyboard V1.1 is always powered from an external 5V power supply connected to V+.

However, when I start my program and it tries to send the first HID packet I get a hard fault if the USB isn't connected. If the USB is connected, everything works fine.

I haven't found a way to sense whether USB is connected; the PA9 (USB_VBUS) pin is high whether USB is connected or not (verified with an oscilloscope on R10). I've tried looking at various STM32 USB OTG_FS registers with no success.

My HID initialization code looks like this:

Code: Select all

	pyb.usb_mode('VCP+HID', hid=(1, 2, 3, 8,
		bytes([0x05, 0x01, 0x09, 0x04, 0xa1, 0x01, 0x09, 0x01,
					0xa1, 0x00, 0x09, 0x30, 0x09, 0x31, 0x09, 0x32,
					0x25, 0x7f, 0x15, 0x81, 0x75, 0x08, 0x95, 0x03,
					0x81, 0x02, 0xc0, 0xc0])))

and I send one-byte X, Y, Z HID packets like this:

Code: Select all

# Send joystick report. Values are -127 to +127.
# hid = pyb.USB_HID()
# hid.send((x, y, z))

Is there some way to avoid this hard fault? I don't have time to dig into this with my JLink.

Thanks!

[pythoncoder]

This is how I do it.

Code: Select all

d_series = os.uname().machine.split(' ')[0][:4] == 'PYBD'
usb_connected = False
if pyb.usb_mode() is not None:  # User has enabled VCP in boot.py
    if d_series:
        # Detect an active debugging session
        usb_connected = pyb.USB_VCP().isconnected()
    else:
        usb_connected = pyb.Pin.board.USB_VBUS.value() == 1

Note that USB is configured as VCP. You say that USB_VBUS isn't working for you, so perhaps it doesn't work in HID mode. Is it possible to check the pin, then reconfigure USB as HID? I'm guessing wildly here as I have no experience with HID mode