## Exercise 05: SD Card Watcher

This exercise continuously watches SD card presence and prints state-change events.

Watcher behavior:

1. Initializes PMU and enables SD power rail (AXP2101 BLDO1).
2. Polls for card changes with debounced state transitions.
3. Emits events only on change:
   - `EVENT: card inserted/mounted`
   - `EVENT: card removed/unavailable`
   - `EVENT: no card detected`
4. On mount event, prints card info and runs SD write workflow.
5. Every 15 seconds while mounted, runs a periodic write/permission check.
6. Uses fast preferred probe (`HSPI @ 400k`) and occasional full fallback scan.

Files used in this exercise:
- `/Exercise_05_test.txt`
- `/test/testsub1/testsubsub1/Exercise_05_test.txt`

## Build

```bash
source /home/jlpoole/rnsenv/bin/activate
pio run -e node_a
```

## Upload

```bash
source /home/jlpoole/rnsenv/bin/activate
pio run -e node_a -t upload --upload-port /dev/ttyACM0
```

## Monitor

```bash
screen /dev/ttyACM0 115200
```