Reserved flash to store some non-volatile state

firmware/Cargo.toml

@@ -26,3 +26,4 @@ cheapsdo-protocol = { path = "../protocol" }
 postcard = {version = "1.0.8", features = ["use-defmt"]} 
 heapless = {version = "0.8.0", features = ["defmt-03"]}
 num = {version = "0.4.1", default-features = false, features = ["libm"]}
+serde = { version = "1.0.195", default-features = false }

firmware/src/config.rs

@@ -0,0 +1,38 @@
+use postcard::{from_bytes_cobs, to_slice_cobs};
+use serde::{Deserialize, Serialize};
+use stm32f1xx_hal::flash::FlashWriter;
+
+#[derive(Serialize, Deserialize, Debug, PartialEq)]
+pub struct Config {
+    pub pwm: u16,
+}
+
+impl Default for Config {
+    fn default() -> Self {
+        Self { pwm: 1500u16 }
+    }
+}
+
+const PAGE_SIZE: usize = 1024;
+const CONFIG_OFFSET: u32 = 63 * PAGE_SIZE as u32;
+
+pub fn load(flash: &mut FlashWriter) -> Config {
+    let tmp = flash.read(CONFIG_OFFSET, PAGE_SIZE).unwrap();
+    let mut config_page = [0u8; PAGE_SIZE];
+    config_page.copy_from_slice(tmp);
+
+    match from_bytes_cobs::<Config>(&mut config_page) {
+        Ok(config) => config,
+        Err(_) => Config::default(),
+    }
+}
+
+impl Config {
+    pub fn save(&self, flash: &mut FlashWriter) {
+        let mut page = [0u8; PAGE_SIZE];
+
+        let used = to_slice_cobs(self, &mut page).unwrap();
+
+        flash.write(CONFIG_OFFSET, &used).unwrap();
+    }
+}

firmware/src/main.rs

@@ -6,6 +6,7 @@ use defmt_rtt as _; // global logger
 use panic_probe as _;
 use stm32f1xx_hal as _;
 
+mod config;
 mod si5153;
 
 // same panicking *behavior* as `panic-probe` but doesn't print a panic message
@@ -41,6 +42,7 @@ mod app {
 
     use cheapsdo_protocol::{DeviceMessage, HostMessage, StatusMessage};
 
+    use crate::config;
     use crate::si5153;
 
     const USB_BUFFER_SIZE: usize = 64;
@@ -229,6 +231,15 @@ mod app {
         si_pll.set_ms_freq(&mut i2c1, si5153::Multisynth::MS0, 100_000_000);
         si_pll.enable_ms_output(&mut i2c1, si5153::Multisynth::MS0);
 
+        let mut writer = flash.writer(
+            stm32f1xx_hal::flash::SectorSize::Sz1K,
+            stm32f1xx_hal::flash::FlashSize::Sz64K,
+        );
+
+        let config = config::load(&mut writer);
+
+        defmt::info!("read config from flash");
+
         update_pwm::spawn().unwrap();
 
         (

memory.x

@@ -1,6 +1,7 @@
 /* Linker script for the STM32F103C8T6 */
 MEMORY
 {
-  FLASH : ORIGIN = 0x08000000, LENGTH = 64K
+  FLASH : ORIGIN = 0x08000000, LENGTH = 63K
+  CONFIG : ORIGIN = FLASH + 63K, LENGTH = 1K
   RAM : ORIGIN = 0x20000000, LENGTH = 20K
 }