GamepadSTM32/boot.py at dev · IsaiahPaget/GamepadSTM32 · GitHub

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# boot.py -- run on boot to configure USB and filesystem
# Put app code in main.py

import machine
import pyb

# Resources:
#   hid spec (https://www.usb.org/sites/default/files/hid1_11.pdf)
#   hid usages and descriptions (https://www.usb.org/sites/default/files/hut1_4.pdf)
#
# The structure goes prefix byte and then value bytes. The prefix is a description of the value bytes not a key like in a map.
# The prefix byte contains 4 bits for the tag, 2 bits for the type and 2 bits for the size, the prefix byte is followed by 0, 1, 2, or 4 value bytes
#
# size: 2 bit expression specifying the size of the value data in bytes
#	00 = 0 bytes
# 	01 = 1 bytes
# 	10 = 2 bytes
# 	11 = 4 bytes (no way to represent 3 bytes)
#
# type: 2 bit expression identifying type of item
#	00 = Main
#	01 = Global
#	10 = Local
#	11 = Reserved
#
# Each type has it's own set of tags which can be found in section 6.2.2 of the hid spec eg. Input(which is a Main item tag) Main with a size of 2:
#	1000 0010 or in hex 0x82

GAMEPAD_REPORT_DESC = bytes([
    0x05, 0x01,        # Usage Page (Generic Desktop)        [Global]
    0x09, 0x05,        # Usage (Gamepad)                     [Local]
    0xA1, 0x01,        # Collection (Application)            [Main]

    # Joysticks usage page is on generic desktop because the hid usages and descriptions says so Generic Desktop (0x01) has many "Usages" some of which are 0x30, 0x31, etc
    0x05, 0x01,        #   Usage Page (Generic Desktop)      [Global]
    0x09, 0x30,        #   Usage (X)                         [Local]
    0x09, 0x31,        #   Usage (Y)                         [Local]
    0x09, 0x32,        #   Usage (Z)                         [Local]
    0x09, 0x33,        #   Usage (Rx)                        [Local]
    0x15, 0x00,        #   Logical Minimum (0)               [Global]
    0x26, 0xFF, 0x00,  #   Logical Maximum (255)             [Global]
    0x75, 0x08,        #   Report Size (8)                   [Global]
    0x95, 0x04,        #   Report Count (4)                  [Global]
    0x81, 0x02,        #   Input (Data, Variable, Absolute)  [Main]
                       #   → 4 axes × 8 bits = 4 bytes

    # Buttons get their own dedicated Usage Page (0x09) rather than living under Generic Desktop
    0x05, 0x09,        #   Usage Page (Button)               [Global]
    0x19, 0x01,        #   Usage Minimum (1)                 [Local]
    0x29, 0x0C,        #   Usage Maximum (12)                [Local]
    0x15, 0x00,        #   Logical Minimum (0)               [Global]
    0x25, 0x01,        #   Logical Maximum (1)               [Global]
    0x75, 0x01,        #   Report Size (1)                   [Global]
    0x95, 0x0C,        #   Report Count (12)                 [Global]
    0x81, 0x02,        #   Input (Data, Variable, Absolute)  [Main]
                       #   → 12 buttons × 1 bit = 12 bits

    # Padding because reports must be byte aligned
    0x95, 0x01,        #   Report Count (1)                  [Global]
    0x75, 0x04,        #   Report Size (4)                   [Global]
    0x81, 0x01,        #   Input (Constant)                  [Main]
                       #   → 1 × 4 bits padding (rounds up to full byte)

    0xC0               # End Collection                      [Main]
])

# Configure USB with custom HID gamepad + serial port
pyb.usb_mode('VCP+HID', hid=(
    0,   # subclass
    0,   # protocol
    64,  # max packet length
    10,  # polling interval in ms
    GAMEPAD_REPORT_DESC
))

# Run main.py after boot
pyb.main('main.py')