TinyUSB Host Keyboard Suspend/Freeze Issues on RP2040

Common Issues

Device Auto-Suspend: Some keyboards automatically enter a low-power suspend mode if they don't detect activity or if the host stops sending Start-Of-Frame (SOF) packets.
Host Controller Freeze: The RP2040 USB host controller can sometimes get into a state where it stops processing events, especially if there are signal integrity issues or if the tuh_task() is blocked for too long.
Missing Keep-Alive: If the host doesn't send SOFs, the device will suspend. The RP2040 host should send SOFs automatically when configured as host.

`tuh_task` Usage

Requirement: tuh_task() must be called continuously and frequently in the main loop.
Blocking: It should not be blocked by long delays (like sleep_ms or blocking display updates) in the same thread.
Current Code: Your hello_usb.cpp calls tuh_task() in a tight loop, which is correct. The display updates are offloaded to Core 1, and the FIFO push is non-blocking (checked with multicore_fifo_wready), so Core 0 should remain responsive.

Potential Fixes & Debugging

1. Handle Suspend/Resume Callbacks

TinyUSB provides callbacks to notify the application when a device suspends or resumes. Implementing these can help determine if the device is actually suspending.

Add these to your hello_usb.cpp:

// Invoked when device is suspended
void tuh_device_suspend_cb(uint8_t dev_addr) {
    printf("Device address = %d suspended\r\n", dev_addr);
}

// Invoked when device is resumed
void tuh_device_resume_cb(uint8_t dev_addr) {
    printf("Device address = %d resumed\r\n", dev_addr);
}

2. Force Resume

If the device suspends and doesn't wake up, you might need to force a resume from the host side, although usually the device initiates resume (remote wakeup) or the host keeps it awake.

3. Check Power

Ensure the keyboard is receiving sufficient power. Some mechanical keyboards with LEDs draw significant current, potentially causing voltage drops that reset the USB connection or cause a freeze.

4. Disable Suspend (Device Side)

Some devices have internal settings to disable sleep, but this is device-specific.

5. SDK/TinyUSB Version

Ensure you are using a recent version of the Pico SDK and TinyUSB, as there have been fixes for RP2040 host mode stability.

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