[−][src]Crate shared_bus
shared-bus is a crate to allow sharing bus peripherals safely between multiple devices.
In the embedded-hal
ecosystem, it is convention for drivers to "own" the bus peripheral they
are operating on. This implies that only one driver can have access to a certain bus. That,
of course, poses an issue when multiple devices are connected to a single bus.
shared-bus solves this by giving each driver a bus-proxy to own which internally manages access to the actual bus in a safe manner. For a more in-depth introduction of the problem this crate is trying to solve, take a look at the blog post.
There are different 'bus managers' for different use-cases:
Sharing within a single task/thread
As long as all users of a bus are contained in a single task/thread, bus sharing is very
simple. With no concurrency possible, no special synchronization is needed. This is where
a BusManagerSimple
should be used:
// For example: // let i2c = I2c::i2c1(dp.I2C1, (scl, sda), 90.khz(), clocks, &mut rcc.apb1); let bus = shared_bus::BusManagerSimple::new(i2c); let mut proxy1 = bus.acquire_i2c(); let mut my_device = MyDevice::new(bus.acquire_i2c()); proxy1.write(0x39, &[0xc0, 0xff, 0xee]); my_device.do_something_on_the_bus();
The BusManager::acquire_*()
methods can be called as often as needed; each call will yield
a new bus-proxy of the requested type.
Sharing across multiple tasks/threads
For sharing across multiple tasks/threads, synchronization is needed to ensure all bus-accesses
are strictly serialized and can't race against each other. The synchronization is handled by
a platform-specific BusMutex
implementation. shared-bus already contains some
implementations for common targets. For each one, there is also a macro for easily creating
a bus-manager with 'static
lifetime, which is almost always a requirement when sharing across
task/thread boundaries. As an example:
// For example: // let i2c = I2c::i2c1(dp.I2C1, (scl, sda), 90.khz(), clocks, &mut rcc.apb1); // The bus is a 'static reference -> it lives forever and references can be // shared with other threads. let bus: &'static _ = shared_bus::new_std!(SomeI2cBus = i2c).unwrap(); let mut proxy1 = bus.acquire_i2c(); let mut my_device = MyDevice::new(bus.acquire_i2c()); // We can easily move a proxy to another thread: std::thread::spawn(move || { my_device.do_something_on_the_bus(); });
Those platform-specific bits are guarded by a feature that needs to be enabled. Here is an overview of what's already available:
Mutex | Bus Manager | 'static Bus Macro | Feature Name |
---|---|---|---|
std::sync::Mutex | BusManagerStd | new_std!() | std |
cortex_m::interrupt::Mutex | BusManagerCortexM | new_cortexm!() | cortex-m |
Supported Busses
Currently, the following busses can be shared with shared-bus:
Bus | Proxy Type | Acquire Method | Comments |
---|---|---|---|
I2C | I2cProxy | .acquire_i2c() | |
SPI | SpiProxy | .acquire_spi() | SPI can only be shared within a single task (See SpiProxy for details). |
Macros
new_cortexm | Macro for creating a Cortex-M bus manager with |
new_std | Macro for creating a |
Structs
BusManager | "Manager" for a shared bus. |
I2cProxy | Proxy type for I2C bus sharing. |
NullMutex | "Dummy" mutex for sharing in a single task/thread. |
SpiProxy | Proxy type for SPI bus sharing. |
Traits
BusMutex | Common interface for mutex implementations. |
Type Definitions
BusManagerCortexM | A bus manager for safely sharing between tasks on Cortex-M. |
BusManagerSimple | A bus manager for sharing within a single task/thread. |
BusManagerStd | A bus manager for safely sharing between threads on a platform with |
CortexMMutex | Alias for a Cortex-M mutex. |