pd200x 0.2.0

Rust driver for the Maono PD200X USB microphone
Documentation 
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

use crate::error::{Error, Result};

pub struct Response {
    pub command: u16,
    pub value: u16,
}

// checksum = -sum(packet[1..end]) & 0xFFFF
fn checksum(packet: &[u8], end: usize) -> u16 {
    let sum: u32 = packet[1..end].iter().map(|&b| b as u32).sum();
    ((!sum).wrapping_add(1)) as u16
}

pub fn build_command_packet(cmd: u16, value: u16) -> [u8; 65] {
    let mut p = [0u8; 65];
    p[0..6].copy_from_slice(&[0x4B, 0xC4, 0x0B, 0x00, 0x00, 0x03]);
    p[6..8].copy_from_slice(&cmd.to_le_bytes());
    p[8..10].copy_from_slice(&value.to_le_bytes());
    let cs = checksum(&p, 10);
    p[10..12].copy_from_slice(&cs.to_le_bytes());
    p
}

pub fn build_query_packet(cmd: u16) -> [u8; 65] {
    let mut p = [0u8; 65];
    p[0..6].copy_from_slice(&[0x4B, 0xC4, 0x09, 0x00, 0x00, 0x04]);
    p[6..8].copy_from_slice(&cmd.to_le_bytes());
    let cs = checksum(&p, 8);
    p[8..10].copy_from_slice(&cs.to_le_bytes());
    p
}

// pairs: [(cmd, value); 5] - one per EQ parameter slot
pub fn build_eq_packet(pairs: [(u16, u16); 5]) -> [u8; 65] {
    let mut p = [0u8; 65];
    p[0..6].copy_from_slice(&[0x4B, 0xC4, 0x1B, 0x00, 0x00, 0x03]);
    let mut offset = 6usize;
    for (cmd, value) in pairs {
        p[offset..offset + 2].copy_from_slice(&cmd.to_le_bytes());
        p[offset + 2..offset + 4].copy_from_slice(&value.to_le_bytes());
        offset += 4;
    }
    // checksum covers bytes 1..0x1A (exclusive), i.e. up to the last value field end
    let cs = checksum(&p, 0x1A);
    p[0x1A..0x1C].copy_from_slice(&cs.to_le_bytes());
    p
}

// Response packets from the device are 64 bytes (not 65 - the device does not
// echo back a report ID byte the way the host transmits one).
pub fn parse_response(raw: &[u8; 64]) -> Result<Response> {
    if raw[1] != 0xC4 {
        return Err(Error::BadResponse);
    }
    let command = u16::from_le_bytes([raw[6], raw[7]]);
    let value = u16::from_le_bytes([raw[8], raw[9]]);
    let stored_cs = u16::from_le_bytes([raw[10], raw[11]]);
    let computed_cs = checksum(raw, 10);
    if stored_cs != computed_cs {
        return Err(Error::BadResponse);
    }
    Ok(Response { command, value })
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn command_packet_checksum_roundtrip() {
        let p = build_command_packet(0x2023, 50);
        assert_eq!(p[0], 0x4B);
        assert_eq!(p[1], 0xC4);
        assert_eq!(p[2], 0x0B);
        // verify checksum recomputation matches stored value
        let stored = u16::from_le_bytes([p[10], p[11]]);
        assert_eq!(stored, checksum(&p, 10));
    }

    #[test]
    fn query_packet_layout() {
        let p = build_query_packet(0x2023);
        assert_eq!(p[2], 0x09);
        assert_eq!(u16::from_le_bytes([p[6], p[7]]), 0x2023);
    }

    #[test]
    fn eq_packet_checksum_roundtrip() {
        let pairs = [
            (0x204D, 1u16),
            (0x204E, 0u16),
            (0x204F, 110u16),
            (0x2050, 2030u16),
            (0x2051, 50u16),
        ];
        let p = build_eq_packet(pairs);
        assert_eq!(p[2], 0x1B);
        let stored = u16::from_le_bytes([p[0x1A], p[0x1B]]);
        assert_eq!(stored, checksum(&p, 0x1A));
    }

    fn make_response(cmd: u16, value: u16) -> [u8; 64] {
        // Simulate a 64-byte device response with the same layout as a command packet.
        let mut raw = [0u8; 64];
        raw[0] = 0x4B;
        raw[1] = 0xC4;
        raw[6..8].copy_from_slice(&cmd.to_le_bytes());
        raw[8..10].copy_from_slice(&value.to_le_bytes());
        let cs = checksum(&raw, 10);
        raw[10..12].copy_from_slice(&cs.to_le_bytes());
        raw
    }

    #[test]
    fn parse_response_rejects_bad_magic() {
        let mut raw = [0u8; 64];
        raw[1] = 0xFF;
        assert!(parse_response(&raw).is_err());
    }

    #[test]
    fn parse_response_rejects_bad_checksum() {
        let mut raw = make_response(0x2023, 50);
        raw[10] ^= 0xFF;
        assert!(parse_response(&raw).is_err());
    }

    #[test]
    fn parse_response_ok() {
        let raw = make_response(0x2023, 50);
        let r = parse_response(&raw).unwrap();
        assert_eq!(r.value, 50);
    }
}