Allow device parameters to be overridden via environment variables

Allow the following parameters to be overridden from their default
values via environment variables:
* Advertised name (for advertising and GAP device name)
* Device id (response to `GetProgressorID` control message)
* Device version number (response to `GetAppVersion` control message)

This allows unique values to be set without committing them to the
repository.

.cargo/config

@@ -17,3 +17,8 @@ runner = "probe-run --chip nRF52832_xxAA"
 
 [build]
 target = "thumbv7em-none-eabihf"     # Cortex-M4F and Cortex-M7F (with FPU)
+
+[env]
+ADVERTISED_NAME = "Progressor_1719"
+DEVICE_ID = "42"
+DEVICE_VERSION_NUMBER = "1.2.3.4"

build.rs

@@ -28,4 +28,7 @@ fn main() {
 
     println!("cargo:rerun-if-changed=build.rs");
     println!("cargo:rerun-if-changed=memory.x");
+    println!("cargo:rerun-if-env-changed=ADVERTISED_NAME");
+    println!("cargo:rerun-if-env-changed=DEVICE_ID");
+    println!("cargo:rerun-if-env-changed=DEVICE_VERSION_NUMBER");
 }

src/ble/gatt_server.rs

@@ -24,9 +24,6 @@ use nrf_softdevice::ble::Connection;
 use nrf_softdevice::Softdevice;
 use once_cell::sync::OnceCell;
 
-const DUMMY_VERSION_NUMBER: &[u8] = b"1.2.3.4";
-const DUMMY_ID: u32 = 42;
-
 #[nrf_softdevice::gatt_server]
 struct Server {
     progressor: ProgressorService,
@@ -129,12 +126,22 @@ fn on_control_message(message: ControlOpcode, conn: &Connection, measure_ch: &Me
             }
         }
         ControlOpcode::GetAppVersion => {
-            if notify_data(DataOpcode::AppVersion(DUMMY_VERSION_NUMBER), conn).is_err() {
+            if notify_data(
+                DataOpcode::AppVersion(env!("DEVICE_VERSION_NUMBER").as_bytes()),
+                conn,
+            )
+            .is_err()
+            {
                 defmt::error!("Response to GetAppVersion failed");
             };
         }
         ControlOpcode::GetProgressorID => {
-            if notify_data(DataOpcode::ProgressorId(DUMMY_ID), conn).is_err() {
+            if notify_data(
+                DataOpcode::ProgressorId(env!("DEVICE_ID").parse().unwrap()),
+                conn,
+            )
+            .is_err()
+            {
                 defmt::error!("Response to GetProgressorID failed");
             };
         }

src/ble/mod.rs

@@ -28,7 +28,7 @@ type MeasureChannel = Sender<'static, NoopRawMutex, weight::Command, MEASURE_COM
 
 /// Device name to be used in GAP and advertising data. The Tindeq app requires this to be
 /// something of this form.
-const ADVERTISED_NAME: &[u8] = b"Progressor_1719";
+const ADVERTISED_NAME: &[u8] = env!("ADVERTISED_NAME").as_bytes();
 
 fn softdevice_config() -> nrf_softdevice::Config {
     use nrf_softdevice::raw;