Newer revisions use LSM303AGR instead of LSM303DLHC

[aditsachde]

Newer revisions of the discovery board use the LSM303AGR instead of the LSM303DLHC. The I2C address of the LSM303AGR chip is still the same but the registers to read are different. This makes it very confusing, as the code doesn't end up panicking, only returning zeros or garbage data.

[eldruin]

Thanks for noticing. I have a WIP driver for the LSM303AGR so you can at least play around with that.
It is actually the same accelerometer as the micro:bit board has, for which this book is being rewritten for (a deprecation/removal of the current book version is still uncertain since the F3 disco board seems available for purchase again)

[aditsachde]

That's great news! Even with the discrepancies the book has, I found this book extremely helpful with dipping my toes into the embedded rust world, and updating the book will help countless more people.

[Winnaries]

Additionally, to make the LSM303AGR works like in the section 14.5 of the discovery book, you have to change its system mode from default idle to continuous mode by modifying the first two bits of the register CFG_REG_A_M via the I2C as well. Otherwise, your (x, y, z) value would probably stuck at some values! Hope this help someone.

[wbuck]

This is for anyone working through the book and you're stuck at the I2C section because the returned value from the IRA_REG_M register is 0.

Here is the link for the LSM303AGR data sheet. As noted above, newer board revisions use this IC instead of the LSM303DLHC.

For a quick test the WHO_AM_I_M register (address 0x4F) of the magnetometer can be used to quickly query the device via I2C.

If successfully you should see 64 or 0b01000000

So the code from the book becomes:

const MAGNETOMETER: u8 = 0b001_1110;
// Addresses of the magnetometer's registers.
const WHO_AM_I_M: u8 = 0x4F;

#[entry]
fn main() -> ! {
    let (i2c1, _delay, mut itm) = aux14::init();

    // Stage 1: Send the address of the register we want to read to the
    // magnetometer
    {
        // Broadcast START
        // Broadcast the MAGNETOMETER address with the R/W bit set to Write
        i2c1.cr2.write(|w| {
            w.start().set_bit();
            w.sadd1().bits(MAGNETOMETER);
            w.rd_wrn().clear_bit();
            w.nbytes().bits(1);
            w.autoend().clear_bit()
        });

        // Wait until we can send more data
        while i2c1.isr.read().txis().bit_is_clear() {}

        // Send the address of the register that we want to read: WHO_AM_I_M
        i2c1.txdr.write(|w| w.txdata().bits(WHO_AM_I_M));

        // Wait until the previous byte has been transmitted
        while i2c1.isr.read().tc().bit_is_clear() {}
    }

    // Stage 2: Receive the contents of the register we asked for
    let byte = {
        // Broadcast RESTART
        // Broadcast the MAGNETOMETER address with the R/W bit set to Read.
        i2c1.cr2.modify(|_, w| {
            w.start().set_bit();
            w.nbytes().bits(1);
            w.rd_wrn().set_bit();
            w.autoend().set_bit()
        });

        // Wait until we have received the contents of the register
        while i2c1.isr.read().rxne().bit_is_clear() {}

        // Broadcast STOP (automatic because of `AUTOEND = 1`)

        i2c1.rxdr.read().rxdata().bits()
    };

    // Expected output:  0b01000000(64)
    iprintln!(&mut itm.stim[0], "0x{:02X} - 0b{:08b}", WHO_AM_I_M, byte);

    loop {}
}

[waalge]

Until there is a rewrite, is it possible to flag this divergence (more?) prominently in the book?

Akin to how the missing solder bridge is nice and big and hard to miss (which I still managed to miss on first read).

[eldruin]

@waalge Sure thing. We would be glad about PRs doing that.

[waalge]

Happy to do more with instruction/ pointers.

When does the book get rebuilt so that changes appear?

[eldruin]

The one hosted at https://rust-embedded.github.io/discovery should be rebuilt shortly after each PR merge. The one hosted at https://docs.rust-embedded.org/discovery is a bit outdated because our CI for it is currently broken. We recently had some discussion about solving this and only publishing one version.

[nargetdev]

Additionally, to make the LSM303AGR works like in the section 14.5 of the discovery book, you have to change its system mode from default idle to continuous mode by modifying the first two bits of the register CFG_REG_A_M via the I2C as well. Otherwise, your (x, y, z) value would probably stuck at some values! Hope this help someone.

Indeed this helped me get to a solution for the LSM303AGR .

Here's my implementation for reading the magnetometer continuously.

#![deny(unsafe_code)]
#![no_main]
#![no_std]

#[allow(unused_imports)]
use aux14::{entry, iprint, iprintln, prelude::*};
use aux14::i2c1::RegisterBlock;

// Slave address
const MAGNETOMETER: u8 = 0b001_1110;

// Addresses of the magnetometer's registers
const OUT_X_H_M: u8 = 0x03;
const IRA_REG_M: u8 = 0x0A;


const WHO_AM_I_M: u8 = 0x4F;

const CFG_REG_A_M: u8 = 0x60;
const OUTX_L_REG_M: u8 = 0x068;

const OUT_X_ACC: u8 = 0x28;

fn set_mode_continuous__LSM303AGR(i2c1: &RegisterBlock) -> (u8) {
    {
        // Broadcast START
        // Broadcast the MAGNETOMETER address with the R/W bit set to Write
        i2c1.cr2.write(|w| {
            w.start().set_bit();
            w.sadd1().bits(MAGNETOMETER);
            w.rd_wrn().clear_bit();
            w.nbytes().bits(2);
            w.autoend().clear_bit()
        });

        // Wait until we can send more data
        while i2c1.isr.read().txis().bit_is_clear() {}

        // Send the address of the register that we want to read: WHO_AM_I_M
        i2c1.txdr.write(|w| w.txdata().bits(CFG_REG_A_M));
        i2c1.txdr.write(|w| w.txdata().bits(0x0));

        // Wait until the previous byte has been transmitted
        while i2c1.isr.read().tc().bit_is_clear() {}
    }

    let cfg_reg_a_m_byte = {
        // Broadcast RESTART
        // Broadcast the MAGNETOMETER address with the R/W bit set to Read.
        i2c1.cr2.modify(|_, w| {
            w.start().set_bit();
            w.nbytes().bits(1);
            w.rd_wrn().set_bit();
            w.autoend().set_bit()
        });

        // Wait until we have received the contents of the register
        while i2c1.isr.read().rxne().bit_is_clear() {}

        // Broadcast STOP (automatic because of `AUTOEND = 1`)

        i2c1.rxdr.read().rxdata().bits()
    };

    cfg_reg_a_m_byte
}

fn who_am_i__LSM303AGR(i2c1: &RegisterBlock) -> u8 {

    // Stage 1: Send the address of the register we want to read to the
    // magnetometer
    {
        // Broadcast START
        // Broadcast the MAGNETOMETER address with the R/W bit set to Write
        i2c1.cr2.write(|w| {
            w.start().set_bit();
            w.sadd1().bits(MAGNETOMETER);
            w.rd_wrn().clear_bit();
            w.nbytes().bits(1);
            w.autoend().clear_bit()
        });

        // Wait until we can send more data
        while i2c1.isr.read().txis().bit_is_clear() {}

        // Send the address of the register that we want to read: WHO_AM_I_M
        i2c1.txdr.write(|w| w.txdata().bits(WHO_AM_I_M));

        // Wait until the previous byte has been transmitted
        while i2c1.isr.read().tc().bit_is_clear() {}
    }

    // Stage 2: Receive the contents of the register we asked for
    let byte = {
        // Broadcast RESTART
        // Broadcast the MAGNETOMETER address with the R/W bit set to Read.
        i2c1.cr2.modify(|_, w| {
            w.start().set_bit();
            w.nbytes().bits(1);
            w.rd_wrn().set_bit();
            w.autoend().set_bit()
        });

        // Wait until we have received the contents of the register
        while i2c1.isr.read().rxne().bit_is_clear() {}

        // Broadcast STOP (automatic because of `AUTOEND = 1`)

        i2c1.rxdr.read().rxdata().bits()
    };

    byte
}

#[entry]
fn main() -> ! {
    let (i2c1, _delay, mut itm) = aux14::init();

    let cfg_reg_a_m_byte: u8 = set_mode_continuous__LSM303AGR(i2c1);
    // Expected output:  0x60 - 0b00000000
    iprintln!(&mut itm.stim[0], "0x{:02X} - 0b{:08b}", CFG_REG_A_M, cfg_reg_a_m_byte);

    let whoami: u8 = who_am_i__LSM303AGR(i2c1);
    // Expected output:  0x4F - 0b01000000
    iprintln!(&mut itm.stim[0], "0x{:02X} - 0b{:08b}", WHO_AM_I_M, whoami);

    // sample magnetometer
    loop{
        // ask for an array of 6 register values starting at OUTX_L_REG_M (0x68)
        {
            // Broadcast START
            // Broadcast the MAGNETOMETER address with the R/W bit set to Write
            i2c1.cr2.write(|w| {
                w.start().set_bit();
                w.sadd1().bits(MAGNETOMETER);
                w.rd_wrn().clear_bit();
                w.nbytes().bits(1);
                w.autoend().clear_bit()
            });

            // Wait until we can send more data
            while i2c1.isr.read().txis().bit_is_clear() {}

            // Send the address of the register that we want to read: WHO_AM_I_M
            i2c1.txdr.write(|w| w.txdata().bits(OUTX_L_REG_M));

            // Wait until the previous byte has been transmitted
            while i2c1.isr.read().tc().bit_is_clear() {}
        }

        i2c1.cr2.modify(|_, w| {
            w.start().set_bit();
            w.nbytes().bits(6);
            w.rd_wrn().set_bit();
            w.autoend().set_bit()
        });

        let mut buffer = [0u8; 6];
        for byte in &mut buffer {
            // Wait until we have received something
            while i2c1.isr.read().rxne().bit_is_clear() {}

            *byte = i2c1.rxdr.read().rxdata().bits();
        }
        // Broadcast STOP (automatic because of `AUTOEND = 1`)

        iprintln!(&mut itm.stim[0], "{:?}", buffer);
    }
}

[folknology]

Also note that the code to convert from the 6 register readings to 3 x i16 have the LSB/MSB order mixed up it should be LSB first :

    let x_l = u16::from(buffer[0]);
    let x_h = u16::from(buffer[1]);
    let z_l = u16::from(buffer[2]);
    let z_h = u16::from(buffer[3]);
    let y_l = u16::from(buffer[4]);
    let y_h = u16::from(buffer[5]);

    let x = ((x_h << 8) + x_l) as i16;
    let y = ((y_h << 8) + y_l) as i16;
    let z = ((z_h << 8) + z_l) as i16;

[pfesenmeier]

@folknology thanks!

p. 45 of AGR datasheet

I'm seeing that the registers are in order x, then y, then z. This is giving me the results I'm getting from using the lsm303agr crate in ch 15.