## Exercise 04: SD Card

This exercise loops forever. Each cycle:

1. Prints `Sleeping 10 seconds` and waits 10 seconds.
2. Detects and mounts the SD card.
3. Prints card and filesystem info (type/size/used).
4. Writes `/Exercise_04_test.txt` with:
   - `This is a test`
5. Ensures nested directories exist:
   - `/test/testsub1/testsubsub1`
6. Writes nested file:
   - `/test/testsub1/testsubsub1/Exercise_04_test.txt`
7. If either target file already exists, prints warning, erases it, then recreates it.
8. Demonstrates permission behavior:
   - Notes FAT does not provide Unix `chmod/chown`.
   - Shows access behavior via `FILE_READ` vs `FILE_WRITE` modes.

## 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
```