1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
//! Instrumentation Trace Macrocell
//!
//! **NOTE** This module is only available on ARMv7-M and newer.

use core::{fmt, ptr, slice};

use crate::peripheral::itm::Stim;

// NOTE assumes that `bytes` is 32-bit aligned
unsafe fn write_words(stim: &mut Stim, bytes: &[u32]) {
    let mut p = bytes.as_ptr();
    for _ in 0..bytes.len() {
        while !stim.is_fifo_ready() {}
        stim.write_u32(ptr::read(p));
        p = p.offset(1);
    }
}

/// Writes an aligned byte slice to the ITM.
///
/// `buffer` must be 4-byte aligned.
unsafe fn write_aligned_impl(port: &mut Stim, buffer: &[u8]) {
    let len = buffer.len();

    if len == 0 {
        return;
    }

    let split = len & !0b11;
    #[allow(clippy::cast_ptr_alignment)]
    write_words(
        port,
        slice::from_raw_parts(buffer.as_ptr() as *const u32, split >> 2),
    );

    // 3 bytes or less left
    let mut left = len & 0b11;
    let mut ptr = buffer.as_ptr().add(split);

    // at least 2 bytes left
    if left > 1 {
        while !port.is_fifo_ready() {}

        #[allow(clippy::cast_ptr_alignment)]
        port.write_u16(ptr::read(ptr as *const u16));

        ptr = ptr.offset(2);
        left -= 2;
    }

    // final byte
    if left == 1 {
        while !port.is_fifo_ready() {}
        port.write_u8(*ptr);
    }
}

struct Port<'p>(&'p mut Stim);

impl<'p> fmt::Write for Port<'p> {
    #[inline]
    fn write_str(&mut self, s: &str) -> fmt::Result {
        write_all(self.0, s.as_bytes());
        Ok(())
    }
}

/// A wrapper type that aligns its contents on a 4-Byte boundary.
///
/// ITM transfers are most efficient when the data is 4-Byte-aligned. This type provides an easy
/// way to accomplish and enforce such an alignment.
#[repr(align(4))]
pub struct Aligned<T: ?Sized>(pub T);

/// Writes `buffer` to an ITM port.
#[allow(clippy::missing_inline_in_public_items)]
pub fn write_all(port: &mut Stim, buffer: &[u8]) {
    unsafe {
        let mut len = buffer.len();
        let mut ptr = buffer.as_ptr();

        if len == 0 {
            return;
        }

        // 0x01 OR 0x03
        if ptr as usize % 2 == 1 {
            while !port.is_fifo_ready() {}
            port.write_u8(*ptr);

            // 0x02 OR 0x04
            ptr = ptr.offset(1);
            len -= 1;
        }

        // 0x02
        if ptr as usize % 4 == 2 {
            if len > 1 {
                // at least 2 bytes
                while !port.is_fifo_ready() {}

                // We checked the alignment above, so this is safe
                #[allow(clippy::cast_ptr_alignment)]
                port.write_u16(ptr::read(ptr as *const u16));

                // 0x04
                ptr = ptr.offset(2);
                len -= 2;
            } else {
                if len == 1 {
                    // last byte
                    while !port.is_fifo_ready() {}
                    port.write_u8(*ptr);
                }

                return;
            }
        }

        // The remaining data is 4-byte aligned, but might not be a multiple of 4 bytes
        write_aligned_impl(port, slice::from_raw_parts(ptr, len));
    }
}

/// Writes a 4-byte aligned `buffer` to an ITM port.
///
/// # Examples
///
/// ```no_run
/// # use cortex_m::{itm::{self, Aligned}, peripheral::ITM};
/// # let port = unsafe { &mut (*ITM::PTR).stim[0] };
/// let mut buffer = Aligned([0; 14]);
///
/// buffer.0.copy_from_slice(b"Hello, world!\n");
///
/// itm::write_aligned(port, &buffer);
///
/// // Or equivalently
/// itm::write_aligned(port, &Aligned(*b"Hello, world!\n"));
/// ```
#[allow(clippy::missing_inline_in_public_items)]
pub fn write_aligned(port: &mut Stim, buffer: &Aligned<[u8]>) {
    unsafe { write_aligned_impl(port, &buffer.0) }
}

/// Writes `fmt::Arguments` to the ITM `port`
#[inline]
pub fn write_fmt(port: &mut Stim, args: fmt::Arguments) {
    use core::fmt::Write;

    Port(port).write_fmt(args).ok();
}

/// Writes a string to the ITM `port`
#[inline]
pub fn write_str(port: &mut Stim, string: &str) {
    write_all(port, string.as_bytes())
}