Use 8 bits of fractional part for PID coefficients

This is needed to set meaningful k_i and k_d coefficients.

Cargo.lock

@@ -299,7 +299,7 @@ dependencies = [
 
 [[package]]
 name = "controller"
-version = "0.6.1"
+version = "0.7.0"
 dependencies = [
  "bootloader-params",
  "build-support",

controller/Cargo.toml

@@ -4,7 +4,7 @@ description = "Firmware for DC Motor Driver Hat DFR0592"
 authors.workspace = true
 edition.workspace = true
 license.workspace = true
-version = "0.6.1"  # Update in python/controller.py as well
+version = "0.7.0"  # Update in python/controller.py as well
 
 [lints]
 workspace = true

controller/python/controller.py

@@ -3,7 +3,7 @@ from numbers import Real
 from typing import Optional
 
 # Major and minor version of required firmware
-_REQUIRED_FIRMWARE_VERSION = (0, 6)
+_REQUIRED_FIRMWARE_VERSION = (0, 7)
 
 
 class FirmwareVersionMismatch(Exception):
@@ -34,7 +34,7 @@ class Controller:
     DEVICE_ID = 0xF0
     FIRMWARE_CAPABILITIES = 0xFE
 
-    PID_COEFFICIENTS_FACTOR = 1 << 4
+    PID_COEFFICIENTS_FACTOR = 1 << 8
 
     def __init__(self, i2c_bus=8):
         import smbus

controller/src/logic/pid_control.rs

@@ -4,7 +4,12 @@ use core::sync::atomic::{AtomicBool, AtomicI16, AtomicI32, Ordering};
 use embassy_time::{Duration, Ticker};
 use pid::{Fixed, Pid};
 
-pub static K_P: AtomicI32 = AtomicI32::new(4);
+type PidUnit = Fixed<8>;
+
+// Those coefficients are to be intepreted as `PidUnit` values.
+// For example, if `PidUnit` is `Fixed<8>`, a value of 0x40 is
+// in fact 0x40 ÷ (1 << 8) = 0.25.
+pub static K_P: AtomicI32 = AtomicI32::new(0x40);
 pub static K_I: AtomicI32 = AtomicI32::new(0);
 pub static K_D: AtomicI32 = AtomicI32::new(0);
 
@@ -12,8 +17,6 @@ static CONTROLLED_MODE: AtomicBool = AtomicBool::new(false);
 static LEFT_SPEED: AtomicI16 = AtomicI16::new(0);
 static RIGHT_SPEED: AtomicI16 = AtomicI16::new(0);
 
-type PidUnit = Fixed<4>;
-
 pub fn disable_controlled_mode() {
     CONTROLLED_MODE.store(false, Ordering::Relaxed);
 }