Datasheet

•
The JMP takes up space in the instruction memory that could be used for other programs
•
The extra cycle taken to execute the JMP ends up halving the maximum output rate
As the Program Counter (PC) naturally wraps to 0 when incremented past 31, we could solve the second of these by
filling the entire instruction memory with a repeating pattern of set pins, 1 and set pins, 0, but this is wasteful. State
machines have a hardware feature, configured via their EXECCTRL control register, which solves this common case.
Pico Examples: https://github.com/raspberrypi/pico-examples/tree/master/pio/squarewave/squarewave_wrap.pio Lines 11 - 19
11 .program squarewave_wrap
12 ; Like squarewave, but use the state machine's .wrap hardware instead of an
13 ; explicit jmp. This is a free (0-cycle) unconditional jump.
14
15 set pindirs, 1 ; Set pin to output
16 .wrap_target
17 set pins, 1 [1] ; Drive pin high and then delay for one cycle
18 set pins, 0 [1] ; Drive pin low and then delay for one cycle
19 .wrap
After executing an instruction from the program memory, state machines use the following logic to update PC:
1.
If the current instruction is a JMP, and the Condition is true, set PC to the Target
2.
Otherwise, if PC matches EXECCTRL_WRAP_TOP, set PC to EXECCTRL_WRAP_BOTTOM
3.
Otherwise, increment PC, or set to 0 if the current value is 31.
The .wrap_target and .wrap assembly directives in pioasm are essentially labels. They export constants which can be
written to the WRAP_BOTTOM and WRAP_TOP control fields, respectively:
Pico Examples: https://github.com/raspberrypi/pico-examples/tree/master/pio/squarewave/generated/squarewave_wrap.pio.h Lines 1 - 37
Ê1 // -------------------------------------------------- //
Ê2 // This file is autogenerated by pioasm; do not edit! //
Ê3 // -------------------------------------------------- //
Ê4
Ê5 #if !PICO_NO_HARDWARE
Ê6 #include "hardware/pio.h"
Ê7 #endif
Ê8
Ê9 // --------------- //
10 // squarewave_wrap //
11 // --------------- //
12
13 #define squarewave_wrap_wrap_target 1
14 #define squarewave_wrap_wrap 2
15
16 static const uint16_t squarewave_wrap_program_instructions[] = {
17 0xe081, // 0: set pindirs, 1
18 // .wrap_target
19 0xe101, // 1: set pins, 1 [1]
20 0xe100, // 2: set pins, 0 [1]
21 // .wrap
22 };
23
24 #if !PICO_NO_HARDWARE
25 static const struct pio_program squarewave_wrap_program = {
26 .instructions = squarewave_wrap_program_instructions,
27 .length = 3,
28 .origin = -1,
29 };
30
RP2040 Datasheet
3.5. Functional Details 352