Make MTU configurable

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Changed
 
 * The default output power interlock threshold has been increased from 0 dBm to 20 dBm.
+* The MTU used for MQTT messages is now configurable in flash.
 
 ### Added
 

src/hardware/external_mac.rs

@@ -2,6 +2,7 @@ use super::Mac;
 use enc424j600::EthPhy;
 
 use smoltcp_nal::smoltcp;
+use super::net_interface::MAX_MTU;
 
 impl smoltcp::phy::Device for Mac {
     type RxToken<'a>
@@ -15,7 +16,7 @@ impl smoltcp::phy::Device for Mac {
 
     fn capabilities(&self) -> smoltcp::phy::DeviceCapabilities {
         let mut caps = smoltcp::phy::DeviceCapabilities::default();
-        caps.max_transmission_unit = 1500;
+        caps.max_transmission_unit = MAX_MTU;
         caps.medium = smoltcp::phy::Medium::Ethernet;
         caps
     }
@@ -24,7 +25,7 @@ impl smoltcp::phy::Device for Mac {
         &mut self,
         _timestamp: smoltcp::time::Instant,
     ) -> Option<(Self::RxToken<'_>, Self::TxToken<'_>)> {
-        let mut buffer = [0u8; 1500];
+        let mut buffer = [0u8; MAX_MTU];
         let len = match self {
             Mac::W5500(w5500) => w5500.read_frame(&mut buffer[..]).unwrap(),
             Mac::Enc424j600(mac) => match mac.recv_packet(false) {
@@ -79,7 +80,7 @@ impl smoltcp::phy::TxToken for TxToken<'_> {
     where
         F: FnOnce(&mut [u8]) -> R,
     {
-        let mut buffer = [0u8; 1500];
+        let mut buffer = [0u8; MAX_MTU];
         let result = f(&mut buffer[..len]);
         match self.mac {
             Mac::W5500(mac) => {

src/hardware/net_interface.rs

@@ -6,6 +6,8 @@ use super::Mac;
 
 /// The number of TCP sockets supported in the network stack.
 const NUM_TCP_SOCKETS: usize = 4;
+/// The maximum MTU configurable for the network interface.
+pub const MAX_MTU: usize = 1500;
 
 /// Containers for smoltcp-related network configurations
 struct NetStorage {

src/hardware/setup.rs

@@ -16,7 +16,7 @@ use super::{
 };
 use stm32f4xx_hal::hal::delay::DelayNs;
 
-use crate::settings::eeprom::main_board::BoosterMainBoardData;
+use crate::settings::eeprom::main_board::{BoosterMainBoardData, Mtu};
 
 use stm32f4xx_hal as hal;
 
@@ -323,6 +323,7 @@ pub fn setup(
         ip: Leaf(eeprom_settings.ip),
         broker: Leaf(eeprom_settings.broker),
         gateway: Leaf(eeprom_settings.gateway),
+        mtu: Leaf(Mtu(eeprom_settings.mtu)),
         id: Leaf(eeprom_settings.id),
         booster: runtime_settings,
     };

src/settings/eeprom/main_board.rs

@@ -23,6 +23,7 @@ use heapless::String;
 use smoltcp_nal::smoltcp;
 
 use crate::hardware::chassis_fans::DEFAULT_FAN_SPEED;
+use crate::hardware::net_interface::MAX_MTU;
 
 use super::{sinara::SinaraConfiguration, SemVersion};
 use serde::{Deserialize, Serialize};
@@ -42,6 +43,26 @@ fn identifier_is_valid(id: &str) -> bool {
     id.len() <= 23 && id.chars().all(|x| x.is_alphanumeric() || x == '-')
 }
 
+#[derive(DeserializeFromStr, Copy, Clone, Debug)]
+pub struct Mtu(pub u16);
+
+impl core::str::FromStr for Mtu {
+    type Err = &'static str;
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let mtu = s.parse::<u16>().map_err(|_| "Invalid MTU format (expected decimal integer)")?;
+        if mtu as usize > MAX_MTU {
+            return Err("Specified MTU exceeds maximum allowed value");
+        }
+        Ok(Self(mtu))
+    }
+}
+
+impl Serialize for Mtu {
+    fn serialize<S: serde::Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
+        serializer.serialize_u16(self.0)
+    }
+}
+
 #[derive(DeserializeFromStr, Copy, Clone, Debug)]
 pub struct IpAddr(pub smoltcp_nal::smoltcp::wire::Ipv4Address);
 
@@ -171,6 +192,7 @@ pub struct SerializedMainBoardData {
     pub netmask: IpAddr,
     pub id: MqttIdentifier,
     pub fan_speed: f32,
+    pub mtu: u16,
 }
 
 impl SerializedMainBoardData {
@@ -189,6 +211,7 @@ impl SerializedMainBoardData {
             gateway: self.gateway,
             id: self.id.0,
             fan_speed: self.fan_speed,
+            mtu: self.mtu,
         }
     }
 }
@@ -203,6 +226,7 @@ pub struct BoosterMainBoardData {
     pub gateway: IpAddr,
     pub id: String<23>,
     pub fan_speed: f32,
+    pub mtu: u16,
 }
 
 impl BoosterMainBoardData {
@@ -238,6 +262,7 @@ impl BoosterMainBoardData {
             gateway: "0.0.0.0".parse().unwrap(),
             id: name,
             fan_speed: DEFAULT_FAN_SPEED,
+            mtu: MAX_MTU as u16,
         }
     }
 
@@ -278,3 +303,24 @@ impl BoosterMainBoardData {
         Ok((config.with_mac(eui48), modified))
     }
 }
+
+
+#[cfg(test)]
+mod tests {
+    // use super::MTU;
+    // use core::str::FromStr;
+    //
+    // // TODO: restructure repo tree to allow logic tests to run not on embedded
+    // //       hardware, but on the host machine
+    // #[test]
+    // fn test_mtu_parsing() {
+    //     let mtu: MTU = MTU::from_str("1500").unwrap();
+    //     assert_eq!(mtu.0, 1500);
+
+    //     let mtu_err = MTU::from_str("1501");
+    //     assert!(mtu_err.is_err());
+
+    //     let mtu_err = MTU::from_str("invalid");
+    //     assert!(mtu_err.is_err());
+    // }
+}

src/settings/mod.rs

@@ -9,6 +9,7 @@ pub mod flash;
 pub mod runtime_settings;
 
 use eeprom::main_board::{Cidr, IpAddr};
+use eeprom::main_board::Mtu;
 use runtime_settings::RuntimeSettings;
 
 #[derive(Clone, Debug, Tree)]
@@ -22,6 +23,7 @@ pub struct Settings {
     pub broker: Leaf<String<255>>,
     pub gateway: Leaf<IpAddr>,
     pub id: Leaf<String<23>>,
+    pub mtu: Leaf<Mtu>,
 }
 
 impl serial_settings::Settings for Settings {
@@ -33,5 +35,6 @@ impl serial_settings::Settings for Settings {
         self.ip = Leaf("0.0.0.0/0".parse().unwrap());
         self.broker = Leaf("mqtt".parse().unwrap());
         self.gateway = Leaf("0.0.0.0".parse().unwrap());
+        self.mtu = Leaf("1500".parse().unwrap());
     }
 }