Revision as of 14:33, 9 August 2022

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