add mosquitto example

controller/README.md

@@ -105,6 +105,17 @@ In order to decode a message, apply the above steps in reverse order.
 
 All configuration is read on startup of the microcontroller.
 
+## MQTT
+
+To read and decode the MQTT messages one can use for example mosquitto as
+follows (using the test.mosquitto.org broker):
+
+```
+mosquitto_sub -h test.mosquitto.org -p 1883 -t "temps/potato" | perl -e 'while(read(STDIN,$b,4)){printf "%.2f\n", unpack("f<",$b)}'
+```
+
+The perl magic is for decoding the floating point little endian representation.
+
 ## Outlook
 
 - Pull the flash/config handling into separate library for testability

controller/src/cmd_handlers/mod.rs

@@ -8,6 +8,7 @@ use serial_comm::{cobs, protocol::set_config::SetConfig};
 use crate::flash::{Config, FlashError};
 
 #[derive(Debug)]
+#[allow(dead_code)]
 pub struct Utf8Error(pub core::str::Utf8Error);
 
 impl Format for Utf8Error {

controller/src/main.rs

@@ -13,7 +13,6 @@ use embassy_executor::Spawner;
 use embassy_net::Stack;
 use embassy_time::Timer;
 use flash::{Config, FlashError};
-use mqtt_protocol::publish::MAX_TOPIC_LENGTH;
 use static_cell::StaticCell;
 use temperature::{temperature_task, Temperature};
 use usb_serial::{init_usb, usb_task};