USB_KEYBOARD_RAWHID Serial Debug Not Working - USB_RAWHID Works Fine

alcnonl42 · May 25, 2025

I'm encountering a puzzling issue with Teensy 4.0 USB configurations and Serial debug output. I have two USB configurations defined in usb_desc.h:

Code:

#elif defined(USB_RAWHID)
  #define VENDOR_ID        0x16C0
  #define PRODUCT_ID        0x0486
  #define RAWHID_USAGE_PAGE    0xFFAB
  #define RAWHID_USAGE        0x0200
  #define MANUFACTURER_NAME    {'T','e','e','n','s','y','d','u','i','n','o'}
  #define MANUFACTURER_NAME_LEN    11
  #define PRODUCT_NAME        {'T','e','e','n','s','y','d','u','i','n','o',' ','R','a','w','H','I','D'}
  #define PRODUCT_NAME_LEN    18
  #define EP0_SIZE        64
  #define NUM_ENDPOINTS         4
  #define NUM_INTERFACE        2
 
  #define RAWHID_INTERFACE      0
  #define RAWHID_TX_ENDPOINT    3
  #define RAWHID_TX_SIZE        64
  #define RAWHID_TX_INTERVAL    1
  #define RAWHID_RX_ENDPOINT    4
  #define RAWHID_RX_SIZE        64
  #define RAWHID_RX_INTERVAL    1
 
  #define SEREMU_INTERFACE      1    // Serial emulation
  #define SEREMU_TX_ENDPOINT    2
  #define SEREMU_TX_SIZE        64
  #define SEREMU_TX_INTERVAL    1
  #define SEREMU_RX_ENDPOINT    2
  #define SEREMU_RX_SIZE        32
  #define SEREMU_RX_INTERVAL    2
 
  #define ENDPOINT2_CONFIG    ENDPOINT_RECEIVE_INTERRUPT + ENDPOINT_TRANSMIT_INTERRUPT
  #define ENDPOINT3_CONFIG    ENDPOINT_RECEIVE_UNUSED + ENDPOINT_TRANSMIT_INTERRUPT
  #define ENDPOINT4_CONFIG    ENDPOINT_RECEIVE_INTERRUPT + ENDPOINT_TRANSMIT_UNUSED

Configuration 2: USB_KEYBOARD_RAWHID (DOESN'T WORK)

Code:

#elif defined(USB_KEYBOARD_RAWHID)
  #define VENDOR_ID               0x16C0
  #define PRODUCT_ID              0x0486
  #define RAWHID_USAGE_PAGE       0xFFAB
  #define RAWHID_USAGE            0x0200
  #define MANUFACTURER_NAME       {'X','x','x','x','x','x','x','x','x'}
  #define MANUFACTURER_NAME_LEN   9
  #define PRODUCT_NAME            {'X','x','x','x','x','x','x','x','x'}
  #define PRODUCT_NAME_LEN        9
  #define EP0_SIZE                64
  #define NUM_ENDPOINTS           6
  #define NUM_INTERFACE           4
                                    
  #define KEYBOARD_INTERFACE      0 
  #define MOUSE_INTERFACE         1
  #define SEREMU_INTERFACE        2
  #define RAWHID_INTERFACE        3 
                                    
  #define KEYBOARD_ENDPOINT       3
  #define KEYBOARD_SIZE           16
  #define KEYBOARD_INTERVAL       1
                                    
  #define MOUSE_ENDPOINT          5
  #define MOUSE_SIZE              8
  #define MOUSE_INTERVAL          1
                                    
  #define SEREMU_TX_ENDPOINT      2
  #define SEREMU_TX_SIZE          64
  #define SEREMU_TX_INTERVAL      1
  #define SEREMU_RX_ENDPOINT      2
  #define SEREMU_RX_SIZE          32
  #define SEREMU_RX_INTERVAL      2
                                    
  #define RAWHID_TX_ENDPOINT      4
  #define RAWHID_TX_SIZE          64
  #define RAWHID_TX_INTERVAL      1
  #define RAWHID_RX_ENDPOINT      6
  #define RAWHID_RX_SIZE          64
  #define RAWHID_RX_INTERVAL      1
                                    
  #define ENDPOINT2_CONFIG        ENDPOINT_RECEIVE_INTERRUPT + ENDPOINT_TRANSMIT_INTERRUPT
  #define ENDPOINT3_CONFIG        ENDPOINT_RECEIVE_UNUSED + ENDPOINT_TRANSMIT_INTERRUPT
  #define ENDPOINT4_CONFIG        ENDPOINT_RECEIVE_UNUSED + ENDPOINT_TRANSMIT_INTERRUPT
  #define ENDPOINT5_CONFIG        ENDPOINT_RECEIVE_UNUSED + ENDPOINT_TRANSMIT_INTERRUPT
  #define ENDPOINT6_CONFIG        ENDPOINT_RECEIVE_INTERRUPT + ENDPOINT_TRANSMIT_UNUSED

The Problem:

USB_RAWHID: Serial debug output works perfectly with Serial.println()
USB_KEYBOARD_RAWHID: No serial debug output appears, even though the code compiles and uploads successfully

Both configurations have identical SEREMU definitions:

Same SEREMU_INTERFACE (though different interface numbers: 1 vs 2)
Same SEREMU endpoints, sizes, and intervals
Same ENDPOINT2_CONFIG for SEREMU

What I've Tried:

Extended Serial.begin() delays (up to 5 seconds)
Added Serial connection timeout checks
Verified SEREMU_INTERFACE is properly defined
Confirmed the Arduino Serial Monitor is working with USB_RAWHID

My Questions:

Why would USB_RAWHID work but USB_KEYBOARD_RAWHID fail for Serial debug when the SEREMU definitions appear identical?
Could there be interface conflicts or enumeration order issues with the additional Keyboard/Mouse interfaces?
Is there something about the endpoint configuration that could prevent SEREMU from functioning properly in the multi-interface configuration?

Environment:

Teensy 4.0
Arduino IDE 1.8.19
Teensyduino 1.58
Custom USB configuration (cannot change USB Type)

I'm particularly puzzled because the SEREMU definitions look functionally identical between the two configurations. Any insights into what might be causing this interface-specific failure would be greatly appreciated.

Has anyone else encountered similar issues with custom USB configurations where adding additional HID interfaces breaks SEREMU functionality?

USB_KEYBOARD_RAWHID Serial Debug Not Working - USB_RAWHID Works Fine

alcnonl42

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