build: create file with current datetime on build

The real-time clock needs an initial date. Extend build.rs to write a file with
the local datetime into OUT_DIR.

Cargo.toml

@@ -23,6 +23,9 @@ rp-pico = "0.8"
 # rp2040-hal = { version="0.9", features=["rt", "critical-section-impl"] }
 # rp2040-boot2 = "0.3"
 
+[build-dependencies]
+chrono = "0.4"
+
 # cargo build/run
 [profile.dev]
 codegen-units = 1

build.rs

@@ -7,7 +7,11 @@
 //! Cargo re-run the build script whenever `memory.x` is changed,
 //! updating `memory.x` ensures a rebuild of the application with the
 //! new memory settings.
+//!
+//! The build script also stores the current time in a Rust file so the
+//! program can set the real-time clock.
 
+use chrono::{self, Datelike, Timelike};
 use std::env;
 use std::fs::File;
 use std::io::Write;
@@ -28,4 +32,48 @@ fn main() {
     // here, we ensure the build script is only re-run when
     // `memory.x` is changed.
     println!("cargo:rerun-if-changed=memory.x");
+
+    let now = chrono::Local::now();
+
+    let mut file = File::create(out.join("build_time.rs")).unwrap();
+    write!(
+        file,
+        "// This file is generated by build.rs and should not be modified manually.
+
+/// Structure containing date and time information
+pub struct DateTime {{
+    /// 0..4095
+    pub year: u16,
+    /// 1..12, 1 is January
+    pub month: u8,
+    /// 1..28,29,30,31 depending on month
+    pub day: u8,
+    ///
+    pub day_of_week: u8,
+    /// 0..23
+    pub hour: u8,
+    /// 0..59
+    pub minute: u8,
+    /// 0..59
+    pub second: u8,
+}}
+
+pub const BUILD_TIME: DateTime = DateTime {{
+    year: {},
+    month: {},
+    day: {},
+    day_of_week: {},
+    hour: {},
+    minute: {},
+    second: {},
+}};",
+        now.year(),
+        now.month(),
+        now.day(),
+        now.weekday().number_from_sunday(),
+        now.hour(),
+        now.minute(),
+        now.second()
+    )
+    .unwrap();
 }

src/digit.rs

@@ -6,6 +6,22 @@ pub type DigitArray = [[u8; NUM_ROWS]; NUM_COLS];
 // X is an alias for readability
 const X: u8 = 1;
 
+const DIGIT_ZERO: DigitArray = transpose([
+    [0, X, X, 0],
+    [X, X, X, X],
+    [X, 0, 0, X],
+    [X, 0, 0, X],
+    [X, 0, 0, X],
+    [X, 0, 0, X],
+    [X, 0, 0, X],
+    [X, 0, 0, X],
+    [X, 0, 0, X],
+    [X, 0, 0, X],
+    [X, 0, 0, X],
+    [X, X, X, X],
+    [0, X, X, 0],
+]);
+
 const DIGIT_ONE: DigitArray = transpose([
     [0, X, X, 0],
     [X, X, X, 0],
@@ -38,7 +54,7 @@ const DIGIT_TWO: DigitArray = transpose([
     [0, 0, X, 0],
 ]);
 
-pub const DIGITS: [DigitArray; 2] = [DIGIT_ONE, DIGIT_TWO];
+pub const DIGITS: [DigitArray; 3] = [DIGIT_ZERO, DIGIT_ONE, DIGIT_TWO];
 
 const fn transpose(arr: [[u8; NUM_COLS]; NUM_ROWS]) -> DigitArray {
     let mut transposed = [[0; NUM_ROWS]; NUM_COLS];

src/main.rs

@@ -5,6 +5,8 @@
 #![no_main]
 #![feature(const_for)]
 
+include!(concat!(env!("OUT_DIR"), "/build_time.rs"));
+
 use bsp::{
     entry,
     hal::gpio::{DynPinId, FunctionSio, Pin, PullDown, SioOutput},
@@ -28,6 +30,19 @@ use bsp::hal::{
 
 mod digit;
 
+fn day_of_week_from_u8(v: u8) -> Result<rtc::DayOfWeek, rtc::DateTimeError> {
+    Ok(match v {
+        0 => rtc::DayOfWeek::Sunday,
+        1 => rtc::DayOfWeek::Monday,
+        2 => rtc::DayOfWeek::Tuesday,
+        3 => rtc::DayOfWeek::Wednesday,
+        4 => rtc::DayOfWeek::Thursday,
+        5 => rtc::DayOfWeek::Friday,
+        6 => rtc::DayOfWeek::Saturday,
+        x => return Err(rtc::DateTimeError::InvalidDayOfWeek(x)),
+    })
+}
+
 #[entry]
 fn main() -> ! {
     info!("Program start");
@@ -52,13 +67,13 @@ fn main() -> ! {
 
     // TODO: read initial datetime from serial
     let initial_date = rtc::DateTime {
-        year: 2023,
-        month: 9,
-        day: 3,
-        day_of_week: rtc::DayOfWeek::Sunday,
-        hour: 14,
-        minute: 14,
-        second: 0,
+        year: BUILD_TIME.year,
+        month: BUILD_TIME.month,
+        day: BUILD_TIME.day,
+        day_of_week: day_of_week_from_u8(BUILD_TIME.day_of_week).unwrap(),
+        hour: BUILD_TIME.hour,
+        minute: BUILD_TIME.minute,
+        second: BUILD_TIME.second,
     };
 
     let real_time_clock =
@@ -128,7 +143,7 @@ fn main() -> ! {
         let k: usize = 0;
         let char_for_digit = now_digits[k];
 
-        if let Some(digit) = digit::DIGITS.get(char_for_digit - 1) {
+        if let Some(digit) = digit::DIGITS.get(char_for_digit) {
             print_digit(digit, &mut row_pins, &mut col_pins, &mut delay, 100, 0.1);
         }
     }