Add NVM read/write functions

Including adding a wrapper type for NVM addresses to provide validation
that the wrong addresses aren't being sent to the device

CHANGELOG.md

@@ -12,8 +12,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `Rn2903::system_factory_reset()`
 - `Rn2903::system_module_reset()`
 - `Rn2903::mac_pause()` and `::mac_resume()`
+- `Rn2903::system_{get, set}_nvm()`
 - `BadResponse` and `CannotPause` error variants
-- Examples directory with LED blinky and LoRa packet RX examples 
+- `NvmAddress` newtype for representing values that can be passed to NVM functions
+- Examples directory:
+    - LED blink
+    - NVM read/write
+    - LoRa packet RX
 
 ### Changed
 

examples/nvm_set_get.rs

@@ -0,0 +1,45 @@
+use rn2903::{NvmAddress, Rn2903};
+use std::env::args;
+use std::process::exit;
+use std::thread;
+use std::time::Duration;
+
+fn main() {
+    let args: Vec<_> = args().collect();
+    if args.len() <= 1 {
+        eprintln!("rn2903_nvm_set_get <serial port>");
+        eprintln!("\tGet, modify, check, and restore the contents of NVM::0x300.");
+        exit(1);
+    }
+
+    let mut txvr = Rn2903::new_at(&args[1]).expect("Could not open device. Error");
+    println!(
+        "Successfully connected. Version: {}",
+        txvr.system_version()
+            .expect("Could not read from device. Error:")
+    );
+
+    txvr.system_module_reset().unwrap();
+    txvr.transact(b"mac pause").unwrap();
+    let addr = NvmAddress::new(0x300);
+
+    txvr.transact(b"sys set pindig GPIO10 1").unwrap();
+    let prev = txvr.system_get_nvm(addr).unwrap();
+    println!("Previous value: {:#x}", prev);
+    txvr.transact(b"sys set pindig GPIO10 0").unwrap();
+
+    txvr.transact(b"sys set pindig GPIO11 1").unwrap();
+    txvr.system_set_nvm(addr, 0xAB).unwrap();
+    println!("Wrote new value");
+    txvr.transact(b"sys set pindig GPIO11 0").unwrap();
+
+    txvr.transact(b"sys set pindig GPIO10 1").unwrap();
+    let new = txvr.system_get_nvm(addr).unwrap();
+    println!("New value: {:#x}", new);
+    txvr.transact(b"sys set pindig GPIO10 0").unwrap();
+
+    txvr.transact(b"sys set pindig GPIO11 1").unwrap();
+    txvr.system_set_nvm(addr, prev).unwrap();
+    println!("Restored old value");
+    txvr.transact(b"sys set pindig GPIO11 0").unwrap();
+}

src/lib.rs

@@ -308,6 +308,34 @@ impl Rn2903 {
     }
 }
 
+/// An address in user-accessible nonvolatile memory. Guaranteed to be between 0x300 and
+/// 0x3FF.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
+pub struct NvmAddress(u16);
+
+impl NvmAddress {
+    /// Create a new `NvmAddress` from a `u16`. The given value must be between 0x300 and
+    /// 0x3FF.
+    ///
+    /// # Panics
+    /// Panics if the given value is not between 0x300 and 0x3FF.
+    pub fn new(value: u16) -> NvmAddress {
+        if value < 0x300 {
+            panic!("Attempted to construct NvmAddress less than 0x300.");
+        }
+        if value > 0x3FF {
+            panic!("Attempted to construct NvmAddress more than 0x3FF.");
+        }
+        NvmAddress(value)
+    }
+
+    /// Return the address to which this NvmAddress refers. Guaranteed to be between
+    /// 0x300 and 0x3FF.
+    pub fn inner(self) -> u16 {
+        self.0
+    }
+}
+
 /// # System API Functions
 impl Rn2903 {
     /// Queries the module for its firmware version information.
@@ -340,6 +368,26 @@ impl Rn2903 {
     pub fn system_factory_reset(&mut self) -> Result<Vec<u8>> {
         self.transact(b"sys factoryRESET")
     }
+
+    /// Set the value of the on-MCU nonvolatile memory at the given address to the given
+    /// value.
+    pub fn system_set_nvm(&mut self, address: NvmAddress, value: u8) -> Result<()> {
+        self.transact_expecting(
+            &format!("sys set nvm {:x} {:x}", address.inner(), value).into_bytes(),
+            b"ok",
+        )
+    }
+
+    /// Get the value of the on-MCU nonvolatile memory at the given address.
+    pub fn system_get_nvm(&mut self, address: NvmAddress) -> Result<u8> {
+        let response = bytes_to_string(
+            &self.transact(&format!("sys get nvm {:x}", address.inner()).into_bytes())?,
+        );
+        match u8::from_str_radix(&response, 16) {
+            Ok(v) => Ok(v),
+            Err(_) => Err(Error::bad_response("<integer>", response)),
+        }
+    }
 }
 
 /// # MAC API Functions