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63 lines
2.4 KiB
Zig
63 lines
2.4 KiB
Zig
//! Hello world for the PIO module: generating a square wave
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const std = @import("std");
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const microzig = @import("microzig");
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const rp2040 = microzig.hal;
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const gpio = rp2040.gpio;
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const Pio = rp2040.pio.Pio;
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const StateMachine = rp2040.pio.StateMachine;
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const squarewave_program = (rp2040.pio.assemble(
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\\.program squarewave
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\\ set pindirs, 1 ; Set pin to output
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\\again:
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\\ set pins, 1 [1] ; Drive pin high and then delay for one cycle
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\\ set pins, 0 ; Drive pin low
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\\ jmp again ; Set PC to label `again`
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, .{}) catch
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@panic("failed to assemble program"))
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.get_program_by_name("squarewave");
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pub fn main() void {
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gpio.reset();
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// Pick one PIO instance arbitrarily. We're also arbitrarily picking state
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// machine 0 on this PIO instance (the state machines are numbered 0 to 3
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// inclusive).
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const pio: Pio = .pio0;
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const sm: StateMachine = .sm0;
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// Load the assembled program directly into the PIO's instruction memory.
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// Each PIO instance has a 32-slot instruction memory, which all 4 state
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// machines can see. The system has write-only access.
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for (squarewave_program.instructions, 0..) |insn, i|
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pio.get_instruction_memory()[i] = insn;
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// Configure state machine 0 to run at sysclk/2.5. The state machines can
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// run as fast as one instruction per clock cycle, but we can scale their
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// speed down uniformly to meet some precise frequency target, e.g. for a
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// UART baud rate. This register has 16 integer divisor bits and 8
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// fractional divisor bits.
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pio.sm_set_clkdiv(sm, .{
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.int = 2,
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.frac = 0x80,
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});
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// There are five pin mapping groups (out, in, set, side-set, jmp pin)
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// which are used by different instructions or in different circumstances.
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// Here we're just using SET instructions. Configure state machine 0 SETs
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// to affect GPIO 0 only; then configure GPIO0 to be controlled by PIO0,
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// as opposed to e.g. the processors.
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pio.gpio_init(0);
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pio.sm_set_pin_mappings(sm, .{
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.out = .{
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.base = 0,
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.count = 1,
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},
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});
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// Set the state machine running. The PIO CTRL register is global within a
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// PIO instance, so you can start/stop multiple state machines
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// simultaneously. We're using the register's hardware atomic set alias to
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// make one bit high without doing a read-modify-write on the register.
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pio.sm_set_enabled(sm, true);
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}
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