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
use embedded_hal_02::blocking::{delay::DelayMs, i2c::WriteRead};
// The EEPROM is a variant without address bits, so the 3 LSB of this word are "dont-cares".
const I2C_ADDR: u8 = 0x50;
// The MAC address is stored in the last 6 bytes of the 256 byte address space.
const MAC_POINTER: u8 = 0xFA;
pub fn read_eui48<T>(i2c: &mut T, delay: &mut impl DelayMs<u8>) -> [u8; 6]
where
T: WriteRead,
{
let mut previous_read: Option<[u8; 6]> = None;
// On Stabilizer v1.1 and earlier hardware, there is a fault where the I2C bus is not connected
// to the CPU until the P12V0A rail enables, which can take many seconds, or may never come up
// at all. During these transient turn-on conditions, we may fail the I2C read operation. To
// accomodate this, we repeat the I2C read for a set number of attempts with a fixed delay
// between them. Then, we wait for the bus to stabilize by waiting until the MAC address
// read-out is identical for two consecutive reads.
for _ in 0..40 {
let mut buffer = [0u8; 6];
if i2c
.write_read(I2C_ADDR, &[MAC_POINTER], &mut buffer)
.is_ok()
{
if let Some(old_read) = previous_read {
if old_read == buffer {
return buffer;
}
}
previous_read.replace(buffer);
} else {
// Remove any pending previous read if we failed the last attempt.
previous_read.take();
}
delay.delay_ms(100);
}
panic!("Failed to read MAC address");
}