Module allocator 

Startup allocator for hardware peripherals, DMA channels, and PIO state machines. Hardware bus allocator.

The allocator hands out peripherals (SPI/I2C/UART), PIO state machines and DMA channels to drivers. Constructed bus handles own their resources for the rest of the boot; the allocator is intentionally a startup-time allocator, not a hot-plug pool. The API is designed so that the most common ways to misconfigure hardware are caught at compile time:

• Pin roles can’t be swapped — clk/mosi/miso and tx/rx are distinguished by trait bounds (ClkPin<I>, MosiPin<I>, …). A pin only implements the role trait for its actual function, so passing miso where clk is expected is a type error.
• Pins can’t be paired with the wrong peripheral instance — the role traits are parameterized by the instance (ClkPin<SPI0> vs ClkPin<SPI1>), so an SPI0 pin can’t be used with the SPI1 peripheral.
• The backend can’t be confused — there are separate create_*_hardware, create_*_pio and create_*_bitbang methods. There is no bool flag and no silent HW→bitbang downgrade when a hardware peripheral was specifically requested.
• DMA channels are owned by the allocator — callers specify which typed channel to use, and the allocator tracks availability. A channel already handed out returns Err(Exhausted).
• PIO state machines are allocated soundly — the PioManager keeps every SM alive, so all 12 SMs are independently available and no (block, sm) combination the allocator returns is unbuild-able.

Async SPI (hardware and PIO) requires DMA. Because embassy-rp models each DMA channel as a distinct type, the caller specifies the channel types (TxDma, RxDma) and provides the board’s IRQ binding; the allocator dispenses the matching Peri tokens from its pool. PIO UART uses FIFO polling (no DMA), so BusAllocator::create_uart provides a PIO→BitBang fallback without DMA for baud rates supported by at least one backend.

Structs

BusAllocator

DmaPool

Set of DMA channels the board hands to the allocator. Fields left as None are not owned by the allocator and can’t be dispensed.

Enums

AllocatorError

Startup-time resource allocation error.

PioBlock

RP235x PIO instances

Sm

RP235x PIO state machine index within a block.

Traits

DmaChannel

A DMA channel the allocator can hand out. Each RP235x DMA channel is a distinct type; the caller specifies which channel(s) to use, and the allocator tracks availability.

I2cHw

A hardware I2C instance the allocator can hand out.

SpiHw

A hardware SPI instance the allocator can hand out.

UartHw

A hardware UART instance the allocator can hand out.