RP2040

Single-cycle IO block (SIO)

Peripherals that require low-latency, deterministic access

CPUID

Core 0 reads a value of 0 when accessing this register, and core 1 reads a value of 1

Integer Divider

8-cycle signed/unsigned divide/modulo unit. Calculation is started by writing a dividend and divisor to the two argument registers, DIVIDEND and DIVISOR. The divider calculates the quotient / and remainder % of this division over the next 8 cycles, and on the 9th cycle the results can be read from the two result registers DIV_QUOTIENT and DIV_REMAINDER. A 'ready' bit in register DIV_CSR can be polled to wait for the calculation to complete, or software can insert a fixed 8-cycle delay.

Interpolator

Each core is equipped with two interpolators which can accelerate tasks by combining certain preconfigured operations into a single processor cycle.

Inter-processor FIFO

Each FIFO is 32 bits wide, and eight entries deep. One of the FIFOs can only be written by core 0, and read by core 1. The other can only be written by core 1, and read by core 0. Each core writes to its outgoing FIFO by writing to FIFO_WR, and reads from its incoming FIFO by reading from FIFO_RD.

A status register, FIFO_ST, provides the following status signals:

• VLD - Incoming FIFO contains data
• RDY - Outgoing FIFO has room for more data
• ROE - The incoming FIFO was read from while empty
• WOF - The outgoing FIFO was written to while full

Hardware Spinlock

The SIO provides 32 hardware spinlocks, which can be used to manage mutually-exclusive access to shared resources. Each spinlock is a one-bit flag, mapped to a different address

• Read: attempt to claim the lock. Read value is nonzero if the lock was successfully claimed, or zero if the lock had already been claimed by a previous read.
• Write (any value): release the lock. The next attempt to claim the lock will be successful.
• If both cores try to claim the same lock on the same clock cycle, core 0 succeeds.

Watchdog

The watchdog is a countdown timer that can restart parts of the chip if it reaches zero. This can be used to restart the processor if software gets stuck in an infinite loop. The programmer must periodically write a value to the watchdog to stop it from reaching zero. Because of a hardware error the watchdog counter is decremented twice per tick.

The watchdog contains eight 32-bit scratch registers that can be used to store information between soft resets of the chip.

DMA

CRC

The DMA can watch data from a given channel passing through the data FIFO, and calculate checksums based on this data.

Types of checksum:

• CRC-32, MSB-first and LSB-first
• CRC-16-CCITT, MSB-first and LSB-first
• Simple summation (add to 32-bit accumulator)
• Even parity

Types of post-processing:

• Bit inversion
• Bit reversal
• Byte swap

Memory

• A 16kB read-only memory (ROM) is at address 0x00000000
• Off-chip execute-in-place (XIP) flash interface (2MB on Raspberry Pi Pico) at address 0x10000000
• Four 16k x 32-bit banks of SRAM (64kB each)
  • Word striped at 0x20000000
  • Non striped at 0x21000000, 0x21010000, 0x21020000 and 0x21030000
• Two 1k x 32-bit banks of SRAM (4kB each) at 0x20040000 and 0x20041000
• If flash XIP caching is disabled, the cache becomes available as 16kB SRAM starting at 0x15000000
• If the USB is not used, the USB data DPRAM can be used as a 4kB memory starting at 0x50100000

Programmable input/output block (PIO)

There are two PIO blocks with four state machines each, that can independently execute sequential programs to manipulate GPIOs and transfer data. Unlike a general purpose processor, PIO state machines are highly specialised for IO, with a focus on determinism, precise timing, and close integration with fixed-function hardware.

Each state machine is equipped with:

• Two 32-bit shift registers – either direction, any shift count
• Two 32-bit scratch registers
• 4×32-bit bus FIFO in each direction (TX/RX), reconfigurable as 8×32 in a single direction
• Fractional clock divider (16 integer, 8 fractional bits)
• Flexible GPIO mapping
• DMA interface, sustained throughput up to 1 word per clock from system DMA
• IRQ flag set/clear/status

Instruction set

All PIO instructions are 16 bits long and execute in a single cycle with no pipeline.

Bit:  15-13 | 12 11 10 9 8   | 7   6   5   | 4 3  2 1 0
JMP   0 0 0 | Delay/side-set | Condition   | Address
WAIT  0 0 1 | Delay/side-set | Pol|Source  | Index
IN    0 1 0 | Delay/side-set | Source      | Bit-count
OUT   0 1 1 | Delay/side-set | Destination | Bit-count
PUSH  1 0 0 | Delay/side-set | 0| IfF |Blk | 0 0  0 0 0
PULL  1 0 0 | Delay/side-set | 1| IfE |Blk | 0 0  0 0 0
MOV   1 0 1 | Delay/side-set | Destination | Op | Source
IRQ   1 1 0 | Delay/side-set | 0|Clr|Wait  | Index
SET   1 1 1 | Delay/side-set | Destination | Data