Use fixed-precision decimal numbers

Cargo.lock

@@ -41,12 +41,24 @@ version = "0.3.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b0a5e3906bcbf133e33c1d4d95afc664ad37fbdb9f6568d8043e7ea8c27d93d3"
 
+[[package]]
+name = "bytemuck"
+version = "1.14.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "374d28ec25809ee0e23827c2ab573d729e293f281dfe393500e7ad618baa61c6"
+
 [[package]]
 name = "byteorder"
 version = "1.4.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "14c189c53d098945499cdfa7ecc63567cf3886b3332b312a5b4585d8d3a6a610"
 
+[[package]]
+name = "cfg-if"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
+
 [[package]]
 name = "cortex-m"
 version = "0.7.7"
@@ -94,6 +106,12 @@ version = "1.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6548a0ad5d2549e111e1f6a11a6c2e2d00ce6a3dafe22948d67c2b443f775e52"
 
+[[package]]
+name = "crunchy"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7a81dae078cea95a014a339291cec439d2f232ebe854a9d672b796c6afafa9b7"
+
 [[package]]
 name = "debug-helper"
 version = "0.3.13"
@@ -175,6 +193,18 @@ dependencies = [
  "void",
 ]
 
+[[package]]
+name = "fixed"
+version = "1.24.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "02c69ce7e7c0f17aa18fdd9d0de39727adb9c6281f2ad12f57cbe54ae6e76e7d"
+dependencies = [
+ "az",
+ "bytemuck",
+ "half",
+ "typenum",
+]
+
 [[package]]
 name = "float-cmp"
 version = "0.9.0"
@@ -199,6 +229,35 @@ version = "2.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1d758ba1b47b00caf47f24925c0074ecb20d6dfcffe7f6d53395c0465674841a"
 
+[[package]]
+name = "half"
+version = "2.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bc52e53916c08643f1b56ec082790d1e86a32e58dc5268f897f313fbae7b4872"
+dependencies = [
+ "cfg-if",
+ "crunchy",
+]
+
+[[package]]
+name = "hash32"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "47d60b12902ba28e2730cd37e95b8c9223af2808df9e902d4df49588d1470606"
+dependencies = [
+ "byteorder",
+]
+
+[[package]]
+name = "heapless"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0bfb9eb618601c89945a70e254898da93b13be0388091d42117462b265bb3fad"
+dependencies = [
+ "hash32",
+ "stable_deref_trait",
+]
+
 [[package]]
 name = "itertools"
 version = "0.10.5"
@@ -407,7 +466,9 @@ dependencies = [
  "display-interface",
  "embedded-graphics",
  "embedded-hal",
+ "fixed",
  "fugit",
+ "heapless",
  "nb 1.1.0",
  "panic-halt",
  "rp-pico",
@@ -446,6 +507,12 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "typenum"
+version = "1.17.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "42ff0bf0c66b8238c6f3b578df37d0b7848e55df8577b3f74f92a69acceeb825"
+
 [[package]]
 name = "unicode-ident"
 version = "1.0.10"

Cargo.toml

@@ -11,7 +11,9 @@ cortex-m-rt = "0.7.3"
 display-interface = "0.4.1"
 embedded-graphics = "0.8.0"
 embedded-hal = "0.2.7"
+fixed = "1.24.0"
 fugit = "0.3.7"
+heapless = "0.8.0"
 nb = "1.1.0"
 panic-halt = "0.2.0"
 rp-pico = "0.7.0"

src/main.rs

@@ -3,7 +3,8 @@
 
 mod max6675;
 
-use core::str;
+use core::fmt::Write;
+use core::write;
 
 use cortex_m::delay::Delay;
 
@@ -23,7 +24,9 @@ use embedded_hal::{
 
 use fugit::{ExtU64, MicrosDurationU64, RateExtU32};
 
-use max6675::{Error, Max6675};
+use heapless::String;
+
+use max6675::{Error, FixedU16, Max6675};
 
 use nb::Error::WouldBlock;
 
@@ -49,19 +52,14 @@ use usb_device::{bus::UsbBus as UsbBusTrait, bus::UsbBusAllocator, prelude::*};
 
 use usbd_serial::{SerialPort, USB_CLASS_CDC};
 
-const HYSTERESIS: u16 = 10;
+const HYSTERESIS: FixedU16 = FixedU16::const_from_int(5);
 
-const PEAK_TEMPERATURE: u16 = 240;
+const PEAK_TEMPERATURE: FixedU16 = FixedU16::const_from_int(240);
 
-const POWER_FACTOR: u16 = 10;
+const PREHEAT_TEMPERATURE: FixedU16 = FixedU16::const_from_int(150);
-const POWER_MAX: u16 = 1000;
-
-const PREHEAT_TEMPERATURE: u16 = 150;
 
 const SOAK_TIME: MicrosDurationU64 = MicrosDurationU64::secs(90);
 
-const TEMPERATURE_BUFF: u16 = 10;
-
 enum State<'a> {
     Off,
     Preheat,
@@ -70,14 +68,6 @@ enum State<'a> {
     Cooling,
 }
 
-fn clamp(value: u16, max: u16) -> u16 {
-    if value > max {
-        max
-    } else {
-        value
-    }
-}
-
 fn print_serial<'a, B: UsbBusTrait>(
     serial: &mut SerialPort<'a, B>,
     msg: &str,
@@ -230,7 +220,6 @@ fn main() -> ! {
     let so = pins.gpio6.into_floating_input();
     let cs = pins.gpio7.into_push_pull_output_in_state(PinState::High);
     let sck = pins.gpio8.into_push_pull_output();
-
     let mut thermocouple = Max6675::new(cs, sck, so);
 
     let button = pins.gpio15.into_pull_up_input();
@@ -246,7 +235,7 @@ fn main() -> ! {
     let mut counter = 0;
     let mut state = State::Off;
     let mut heating = false;
-    let mut power = 0;
+    let mut error_counter = 0;
     loop {
         delay.delay_ms(5);
         counter = (counter + 1) % 2000;
@@ -271,15 +260,13 @@ fn main() -> ! {
         if counter % 50 == 0 {
             let thermocouple_result = thermocouple.read_temperature(&mut timer.count_down());
 
-            if let Some(mut temperature) = thermocouple_result.as_ref().copied().ok() {
+            if let Some(temperature) = thermocouple_result.as_ref().copied().ok() {
-                temperature = (temperature >> 2) + ((temperature & 2) >> 1);
+                error_counter = 0;
 
                 match state {
-                    State::Off => (),
                     State::Preheat => {
                         if temperature < PREHEAT_TEMPERATURE {
                             heating = true;
-                            power = clamp((PREHEAT_TEMPERATURE - temperature + TEMPERATURE_BUFF) * POWER_FACTOR, POWER_MAX);
                         } else {
                             let mut time = timer.count_down();
                             time.start(SOAK_TIME);
@@ -289,58 +276,61 @@ fn main() -> ! {
                     State::Soak(ref mut time) => match time.wait() {
                         Ok(_) => state = State::Reflow,
                         Err(WouldBlock) => {
-                            if temperature < PREHEAT_TEMPERATURE - HYSTERESIS {
+                            if temperature < PREHEAT_TEMPERATURE {
                                 heating = true;
-                                power = clamp((PREHEAT_TEMPERATURE - temperature + TEMPERATURE_BUFF) * POWER_FACTOR, POWER_MAX);
+                            }
-                            } else if temperature > PREHEAT_TEMPERATURE + HYSTERESIS * 2 {
+                            if temperature > PREHEAT_TEMPERATURE + HYSTERESIS {
-                                state = State::Reflow;
-                            } else if temperature > PREHEAT_TEMPERATURE {
                                 heating = false;
                             }
                         }
-                        Err(_) => state = State::Off,
+                        Err(_) => unreachable!(),
                     },
                     State::Reflow => {
                         if temperature < PEAK_TEMPERATURE {
                             heating = true;
-                            power = clamp((PEAK_TEMPERATURE - temperature + TEMPERATURE_BUFF) * POWER_FACTOR, POWER_MAX);
                         } else {
                             heating = false;
 
                             state = State::Cooling;
                         }
                     }
-                    State::Cooling => state = State::Off,
+                    State::Cooling if temperature < PREHEAT_TEMPERATURE => {
+                        state = State::Preheat;
+                    }
+                    _ => (),
                 }
             } else {
+                error_counter += 1;
+            }
+
+            if error_counter >= 4 {
                 state = State::Off;
             }
 
-            let mut bytes: [u8; 7] = [32, 32, 32, 32, 194, 176, 67];
+            let mut text: String<9> = String::new();
-            let text = match thermocouple_result {
+            let text_str;
-                Ok(mut temperature) => {
-                    temperature = (temperature >> 2) + ((temperature & 2) >> 1);
 
-                    for i in (0..3).rev() {
+            match thermocouple_result {
-                        bytes[i] = 48u8 + (temperature % 10) as u8;
+                Ok(temperature) => {
-                        temperature /= 10;
+                    if let Err(_) = write!(&mut text, "{}", temperature) {
-
+                        text_str = "format error";
-                        if temperature == 0 {
+                    } else {
-                            break;
+                        text_str = text.as_str();
-                        }
                     }
-
-                    str::from_utf8(&bytes).unwrap()
                 }
-                Err(Error::IOError) => "i/o error",
+                Err(Error::IOError) => {
-                Err(Error::OpenThermocouple) => "n/c",
+                    text_str = "i/o error";
+                }
+                Err(Error::OpenThermocouple) => {
+                    text_str = "n/c";
+                }
             };
 
-            let _ = println_serial(&mut serial, text);
+            let _ = println_serial(&mut serial, text_str);
 
             display.clear_buffer();
 
-            if let Err(err) = display_text(&mut display, text, Baseline::Bottom) {
+            if let Err(err) = display_text(&mut display, text_str, Baseline::Bottom) {
                 let _ = println_serial(&mut serial, stringify_display_error(err));
             }
 
@@ -362,16 +352,11 @@ fn main() -> ! {
         }
 
         if let State::Off = state {
-            relay.set_low().unwrap();
             heating = false;
         }
 
         if heating {
-            if counter == 0 {
+            relay.set_high().unwrap();
-                relay.set_high().unwrap();
-            } else if counter >= power {
-                relay.set_low().unwrap();
-            }
         } else {
             relay.set_low().unwrap();
         }

src/max6675.rs

@@ -3,10 +3,14 @@ use embedded_hal::{
     timer::CountDown,
 };
 
+use fixed::types::extra::U2;
+
 use fugit::{ExtU64, MicrosDurationU64};
 
 use nb::block;
 
+pub type FixedU16 = fixed::FixedU16<U2>;
+
 #[derive(Debug)]
 pub enum Error {
     IOError,
@@ -34,7 +38,7 @@ where
         Self { cs, sck, so }
     }
 
-    pub fn read_temperature<CD>(&mut self, timer: &mut CD) -> Result<u16, Error>
+    pub fn read_temperature<CD>(&mut self, timer: &mut CD) -> Result<FixedU16, Error>
     where
         CD: CountDown,
         CD::Time: From<MicrosDurationU64>,
@@ -61,7 +65,7 @@ where
         if d & 0x4 == 0x4 {
             Err(Error::OpenThermocouple)
         } else {
-            Ok(d >> 3)
+            Ok(FixedU16::from_num(d >> 3))
         }
     }
 }