PCA9548A Driver

PCA9548a I2C-Expander driver using embedded-hal.

Simple Usage

You can select one ore more channels to activate.

use pca9548a::{Pca9548a, BASE_ADDRESS};
use embedded_hal::i2c::I2c;

let pca = Pca9548a::<std::sync::Mutex<_>>::new(i2c_bus, BASE_ADDRESS);

// `select_*()` returns an i2c-bus that can be used to perform transactions.
pca.select_single(0).unwrap().write(0x42, &[1, 2]).unwrap();
pca.select_mask(1 << 2 | 1 << 3).unwrap().write(0x42, &[1, 2]).unwrap();

SubBus

Often you will want to use device drivers that expect to take ownership of a type implementing I2c.

For this a proxy type SubBus is provided that implements embedded_hal::i2c::I2c/embedded_hal_async::i2c::I2c (depending on the underlying mutex and i2c bus implementations).

You can even use it to cascade PCA9548As:

use pca9548a::{Pca9548a, BASE_ADDRESS};

let pca = Pca9548a::<std::sync::Mutex<_>>::new(i2c_bus, BASE_ADDRESS);
// NOTE: If you chain PCA9548As, they must have different addresses
let pca_0 = Pca9548a::<std::sync::Mutex<_>>::new(pca.single_subbus(0), BASE_ADDRESS + 1);
let pca_1 = Pca9548a::<std::sync::Mutex<_>>::new(pca.single_subbus(1), BASE_ADDRESS + 1);
let pca_1_7 = Pca9548a::<std::sync::Mutex<_>>::new(pca_1.single_subbus(7), BASE_ADDRESS + 2);

// This will correctly select the channel 1 on pca, then channel 7 on pca_1, then channel 3 on pca_1_7
// before writing [1, 2] to address 0x42.
pca_1_7.select_single(3).unwrap().write(0x42, &[1, 2]).unwrap();

Note on SharedBus

This driver requires shared access to the underlying i2c bus similar to the shared_bus crate. A mutex is used to implement this.

When selecting a set of channels, a lock to the i2c-bus is returned; this can be used to perform transactions and prevents other tasks changing the selection before you are done.

However, this assumes that the Pca9548a struct has exclusive access to the underlying i2c bus. If you use shared_bus or similar, you must make sure that other tasks cannot change the selection, as this may break the guarantee that the correct channels are selected.