# TinyUSB Host Keyboard Suspend/Freeze Issues on RP2040

## Common Issues
1. **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.
2. **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.
3. **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`:

```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.
