rp/pio: add hd44780 example
add an hd44780 example for pio. hd44780 with busy polling is a pretty complicated protocol if the busy polling is to be done by the peripheral, and this example exercises many pio features that we don't have good examples for yet.
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examples/rp/src/bin/pio_hd44780.rs
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244
examples/rp/src/bin/pio_hd44780.rs
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#![no_std]
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#![no_main]
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#![feature(type_alias_impl_trait)]
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use core::fmt::Write;
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use embassy_executor::Spawner;
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use embassy_rp::dma::{AnyChannel, Channel};
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use embassy_rp::gpio::Pin;
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use embassy_rp::peripherals::PIO0;
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use embassy_rp::pio::{
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FifoJoin, PioCommon, PioInstanceBase, PioPeripheral, PioStateMachine, PioStateMachineInstance, ShiftDirection,
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SmInstanceBase,
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};
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use embassy_rp::pwm::{Config, Pwm};
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use embassy_rp::relocate::RelocatedProgram;
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use embassy_rp::{into_ref, Peripheral, PeripheralRef};
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use embassy_time::{Duration, Instant, Timer};
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use {defmt_rtt as _, panic_probe as _};
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#[embassy_executor::main]
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async fn main(_spawner: Spawner) {
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// this test assumes a 2x16 HD44780 display attached as follow:
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// rs = PIN0
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// rw = PIN1
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// e = PIN2
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// db4 = PIN3
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// db5 = PIN4
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// db6 = PIN5
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// db7 = PIN6
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// additionally a pwm signal for a bias voltage charge pump is provided on pin 15,
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// allowing direct connection of the display to the RP2040 without level shifters.
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let p = embassy_rp::init(Default::default());
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let _pwm = Pwm::new_output_b(p.PWM_CH7, p.PIN_15, {
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let mut c = Config::default();
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c.divider = 125.into();
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c.top = 100;
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c.compare_b = 50;
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c
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});
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let mut hd = HD44780::new(
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p.PIO0, p.DMA_CH3, p.PIN_0, p.PIN_1, p.PIN_2, p.PIN_3, p.PIN_4, p.PIN_5, p.PIN_6,
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)
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.await;
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loop {
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struct Buf<const N: usize>([u8; N], usize);
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impl<const N: usize> Write for Buf<N> {
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fn write_str(&mut self, s: &str) -> Result<(), core::fmt::Error> {
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for b in s.as_bytes() {
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if self.1 >= N {
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return Err(core::fmt::Error);
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}
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self.0[self.1] = *b;
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self.1 += 1;
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}
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Ok(())
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}
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}
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let mut buf = Buf([0; 16], 0);
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write!(buf, "up {}s", Instant::now().as_micros() as f32 / 1e6).unwrap();
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hd.add_line(&buf.0[0..buf.1]).await;
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Timer::after(Duration::from_secs(1)).await;
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}
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}
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pub struct HD44780<'l> {
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dma: PeripheralRef<'l, AnyChannel>,
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sm: PioStateMachineInstance<PioInstanceBase<0>, SmInstanceBase<0>>,
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buf: [u8; 40],
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}
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impl<'l> HD44780<'l> {
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pub async fn new(
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pio: PIO0,
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dma: impl Peripheral<P = impl Channel> + 'l,
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rs: impl Pin,
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rw: impl Pin,
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e: impl Pin,
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db4: impl Pin,
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db5: impl Pin,
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db6: impl Pin,
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db7: impl Pin,
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) -> HD44780<'l> {
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into_ref!(dma);
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let db7pin = db7.pin();
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let (mut common, mut sm0, ..) = pio.split();
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// takes command words (<wait:24> <command:4> <0:4>)
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let prg = pio_proc::pio_asm!(
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r#"
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.side_set 1 opt
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loop:
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out x, 24
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delay:
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jmp x--, delay
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out pins, 4 side 1
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out null, 4 side 0
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jmp !osre, loop
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irq 0
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"#,
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);
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let rs = common.make_pio_pin(rs);
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let rw = common.make_pio_pin(rw);
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let e = common.make_pio_pin(e);
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let db4 = common.make_pio_pin(db4);
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let db5 = common.make_pio_pin(db5);
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let db6 = common.make_pio_pin(db6);
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let db7 = common.make_pio_pin(db7);
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sm0.set_set_pins(&[&rs, &rw]);
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embassy_rp::pio_instr_util::set_pindir(&mut sm0, 0b11);
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sm0.set_set_pins(&[&e]);
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embassy_rp::pio_instr_util::set_pindir(&mut sm0, 0b1);
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sm0.set_set_pins(&[&db4, &db5, &db6, &db7]);
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embassy_rp::pio_instr_util::set_pindir(&mut sm0, 0b11111);
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let relocated = RelocatedProgram::new(&prg.program);
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common.write_instr(relocated.origin() as usize, relocated.code());
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embassy_rp::pio_instr_util::exec_jmp(&mut sm0, relocated.origin());
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sm0.set_clkdiv(125 * 256);
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let pio::Wrap { source, target } = relocated.wrap();
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sm0.set_wrap(source, target);
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sm0.set_side_enable(true);
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sm0.set_out_pins(&[&db4, &db5, &db6, &db7]);
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sm0.set_sideset_base_pin(&e);
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sm0.set_sideset_count(2);
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sm0.set_out_shift_dir(ShiftDirection::Left);
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sm0.set_fifo_join(FifoJoin::TxOnly);
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sm0.set_autopull(true);
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sm0.set_pull_threshold(32);
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sm0.set_enable(true);
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// init to 8 bit thrice
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sm0.push_tx((50000 << 8) | 0x30);
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sm0.push_tx((5000 << 8) | 0x30);
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sm0.push_tx((200 << 8) | 0x30);
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// init 4 bit
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sm0.push_tx((200 << 8) | 0x20);
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// set font and lines
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sm0.push_tx((50 << 8) | 0x20);
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sm0.push_tx(0b1100_0000);
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sm0.wait_irq(0).await;
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sm0.set_enable(false);
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// takes command sequences (<rs:1> <count:7>, data...)
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// many side sets are only there to free up a delay bit!
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let prg = pio_proc::pio_asm!(
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r#"
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.origin 7
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.side_set 1
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.wrap_target
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pull side 0
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out x 1 side 0 ; !rs
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out y 7 side 0 ; #data - 1
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; rs/rw to e: >= 60ns
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; e high time: >= 500ns
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; e low time: >= 500ns
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; read data valid after e falling: ~5ns
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; write data hold after e falling: ~10ns
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loop:
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pull side 0
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jmp !x data side 0
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command:
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set pins 0b00 side 0
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jmp shift side 0
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data:
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set pins 0b01 side 0
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shift:
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out pins 4 side 1 [9]
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nop side 0 [9]
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out pins 4 side 1 [9]
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mov osr null side 0 [7]
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out pindirs 4 side 0
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set pins 0b10 side 0
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busy:
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nop side 1 [9]
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jmp pin more side 0 [9]
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mov osr ~osr side 1 [9]
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nop side 0 [4]
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out pindirs 4 side 0
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jmp y-- loop side 0
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.wrap
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more:
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nop side 1 [9]
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jmp busy side 0 [9]
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"#
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);
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let relocated = RelocatedProgram::new(&prg.program);
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common.write_instr(relocated.origin() as usize, relocated.code());
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embassy_rp::pio_instr_util::exec_jmp(&mut sm0, relocated.origin());
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let pio::Wrap { source, target } = relocated.wrap();
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sm0.set_clkdiv(8 * 256); // ~64ns/insn
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sm0.set_side_enable(false);
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sm0.set_jmp_pin(db7pin);
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sm0.set_wrap(source, target);
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sm0.set_set_pins(&[&rs, &rw]);
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sm0.set_out_pins(&[&db4, &db5, &db6, &db7]);
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sm0.set_sideset_base_pin(&e);
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sm0.set_sideset_count(1);
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sm0.set_out_shift_dir(ShiftDirection::Left);
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sm0.set_fifo_join(FifoJoin::TxOnly);
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sm0.set_enable(true);
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// display on and cursor on and blinking, reset display
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sm0.dma_push(dma.reborrow(), &[0x81u8, 0x0f, 1]).await;
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Self {
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dma: dma.map_into(),
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sm: sm0,
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buf: [0x20; 40],
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}
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}
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pub async fn add_line(&mut self, s: &[u8]) {
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// move cursor to 0:0, prepare 16 characters
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self.buf[..3].copy_from_slice(&[0x80, 0x80, 15]);
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// move line 2 up
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self.buf.copy_within(22..38, 3);
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// move cursor to 1:0, prepare 16 characters
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self.buf[19..22].copy_from_slice(&[0x80, 0xc0, 15]);
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// file line 2 with spaces
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self.buf[22..38].fill(0x20);
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// copy input line
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let len = s.len().min(16);
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self.buf[22..22 + len].copy_from_slice(&s[0..len]);
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// set cursor to 1:15
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self.buf[38..].copy_from_slice(&[0x80, 0xcf]);
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self.sm.dma_push(self.dma.reborrow(), &self.buf).await;
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}
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}
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