# Overview

This is the b-parasite formware based on Nordic's [nRF5 SDK](https://infocenter.nordicsemi.com/index.jsp?topic=%2Fstruct_sdk%2Fstruct%2Fsdk_nrf5_latest.html&cp=7_1).

It uses Nordic's SoftDevice, which should additionally be flashed to the chip before running our firmware.

I use a [JLink probe](https://www.segger.com/products/debug-probes/j-link/) for flashing and debugging.

# Configuration
The b-parasite specific configuration, such as active/sleep time  and transmitting power are defined in [config/prst_config.h](./config/prst_config.h).

# Flashing SoftDevice and Firmware
```bash
# Flash softdevice
$ SDK_ROOT=~/dev/nrf52/sdk/nRF5_SDK_17.0.2_d674dde make flash_softdevice
# Compile annd flash our firmware
$ SDK_ROOT=~/dev/nrf52/sdk/nRF5_SDK_17.0.2_d674dde make flash
```

# Debugging
Calls to `NRF_LOG` will be readable on the console using `JLinkRTTLogger`. This is the handy one-liner I use for pulling log messages:

```bash
$ echo "\n\n\n\n0\n/dev/stdout" | JLinkRTTLogger | sed 's/^.*app: //'
```

# Bluetooth Low Energy Advertisement Data Encoding
Sensor data is encoded in the BLE advertisement packet as Service Data for the [Environmental Sensing Service profile](https://www.bluetooth.com/specifications/assigned-numbers/environmental-sensing-service-characteristics/) (UUID 0x181a).

Sensor data is encoded in unsigned 16 bits (2 bytes), and whenever multiple
 bytes are used to represent a single value, the encoding is big-endian.

| Byte index |                          Description                           |
|------------|----------------------------------------------------------------|
| 0          | 4 bits for protocol version + 4 reserved bits                  |
| 1          | 4 reserved bits + 4 bits wrap-around counter for deduplication |
| 2-3        | Battery voltage in millivolts                                  |
| 4-5        | Temperature in millidegrees Celcius                            |
| 6-7        | Relative air humidity, scaled from 0 (0%) to 0xffff (100%)     |
| 8-9        | Soil moisture, scaled from from 0 (0%) to 0xffff (100%)        |
| 10-15      | b-parasite's own MAC address, big-endian format                |