rtc_hal/
bcd.rs

1//! # BCD (Binary Coded Decimal) conversion utilities for RTC operations
2//!
3//! This module provides conversion functions between BCD and decimal formats
4//! commonly used in Real-Time Clock (RTC) chips like the DS1307.
5//!
6//! ## BCD Format Overview
7//!
8//! Binary Coded Decimal (BCD) represents decimal digits using 4-bit binary patterns:
9//! - Each decimal digit (0-9) is encoded in 4 bits
10//! - One byte can hold two decimal digits (00-99)
11//! - High nibble = tens digit, low nibble = ones digit
12//!
13//! ## Format Examples
14//!
15//! | Decimal | BCD Binary   | BCD Hex |
16//! |---------|--------------|---------|
17//! | 00      | 0000 0000    | 0x00    |
18//! | 01      | 0000 0001    | 0x01    |
19//! | 09      | 0000 1001    | 0x09    |
20//! | 10      | 0001 0000    | 0x10    |
21//! | 23      | 0010 0011    | 0x23    |
22//! | 59      | 0101 1001    | 0x59    |
23//! | 99      | 1001 1001    | 0x99    |
24//!
25
26/// Convert a BCD encoded byte to decimal
27/// First 4 bits are tens of the number
28/// Last 4 bits are ones of the number
29pub fn to_decimal(bcd: u8) -> u8 {
30    ((bcd >> 4) * 10) + (bcd & 0x0F)
31}
32
33/// Convert decimal byte to BCD encoding
34pub fn from_decimal(decimal: u8) -> u8 {
35    debug_assert!(decimal <= 99, "Decimal value must be <= 99 for BCD");
36    ((decimal / 10) << 4) | (decimal % 10)
37}
38
39#[cfg(test)]
40mod tests {
41    use super::*;
42
43    #[test]
44    fn test_to_decimal() {
45        assert_eq!(to_decimal(0x00), 0);
46        assert_eq!(to_decimal(0x01), 1);
47        assert_eq!(to_decimal(0x09), 9);
48        assert_eq!(to_decimal(0x10), 10);
49        assert_eq!(to_decimal(0x23), 23);
50        assert_eq!(to_decimal(0x45), 45);
51        assert_eq!(to_decimal(0x59), 59);
52        assert_eq!(to_decimal(0x99), 99);
53    }
54
55    #[test]
56    fn test_from_decimal() {
57        assert_eq!(from_decimal(0), 0x00);
58        assert_eq!(from_decimal(1), 0x01);
59        assert_eq!(from_decimal(9), 0x09);
60        assert_eq!(from_decimal(10), 0x10);
61        assert_eq!(from_decimal(23), 0x23);
62        assert_eq!(from_decimal(45), 0x45);
63        assert_eq!(from_decimal(59), 0x59);
64        assert_eq!(from_decimal(99), 0x99);
65    }
66
67    #[test]
68    fn test_bcd_round_trip() {
69        for i in 0..=99 {
70            let bcd = from_decimal(i);
71            let decimal = to_decimal(bcd);
72            assert_eq!(i, decimal);
73        }
74    }
75
76    #[test]
77    fn test_bcd_edge_cases() {
78        // Test boundary values commonly used in RTC
79        let test_cases = [0, 1, 9, 10, 23, 31, 59, 99];
80
81        for &value in &test_cases {
82            let bcd = from_decimal(value);
83            let back = to_decimal(bcd);
84            assert_eq!(value, back, "Failed for value: {value}");
85        }
86    }
87}
rtc_hal/bcd.rs

rtc_hal/
bcd.rs
