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.

1 files changed, 244 insertions, 0 deletions

diff --git a/examples/rp/src/bin/pio_hd44780.rs b/examples/rp/src/bin/pio_hd44780.rs
new file mode 100644
index 000000000..6bcd0652b
--- /dev/null
+++ b/examples/rp/src/bin/pio_hd44780.rs
@@ -0,0 +1,244 @@
+#![no_std]
+#![no_main]
+#![feature(type_alias_impl_trait)]
+
+use core::fmt::Write;
+
+use embassy_executor::Spawner;
+use embassy_rp::dma::{AnyChannel, Channel};
+use embassy_rp::gpio::Pin;
+use embassy_rp::peripherals::PIO0;
+use embassy_rp::pio::{
+    FifoJoin, PioCommon, PioInstanceBase, PioPeripheral, PioStateMachine, PioStateMachineInstance, ShiftDirection,
+    SmInstanceBase,
+};
+use embassy_rp::pwm::{Config, Pwm};
+use embassy_rp::relocate::RelocatedProgram;
+use embassy_rp::{into_ref, Peripheral, PeripheralRef};
+use embassy_time::{Duration, Instant, Timer};
+use {defmt_rtt as _, panic_probe as _};
+
+#[embassy_executor::main]
+async fn main(_spawner: Spawner) {
+    // this test assumes a 2x16 HD44780 display attached as follow:
+    //   rs  = PIN0
+    //   rw  = PIN1
+    //   e   = PIN2
+    //   db4 = PIN3
+    //   db5 = PIN4
+    //   db6 = PIN5
+    //   db7 = PIN6
+    // additionally a pwm signal for a bias voltage charge pump is provided on pin 15,
+    // allowing direct connection of the display to the RP2040 without level shifters.
+    let p = embassy_rp::init(Default::default());
+
+    let _pwm = Pwm::new_output_b(p.PWM_CH7, p.PIN_15, {
+        let mut c = Config::default();
+        c.divider = 125.into();
+        c.top = 100;
+        c.compare_b = 50;
+        c
+    });
+
+    let mut hd = HD44780::new(
+        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,
+    )
+    .await;
+
+    loop {
+        struct Buf<const N: usize>([u8; N], usize);
+        impl<const N: usize> Write for Buf<N> {
+            fn write_str(&mut self, s: &str) -> Result<(), core::fmt::Error> {
+                for b in s.as_bytes() {
+                    if self.1 >= N {
+                        return Err(core::fmt::Error);
+                    }
+                    self.0[self.1] = *b;
+                    self.1 += 1;
+                }
+                Ok(())
+            }
+        }
+        let mut buf = Buf([0; 16], 0);
+        write!(buf, "up {}s", Instant::now().as_micros() as f32 / 1e6).unwrap();
+        hd.add_line(&buf.0[0..buf.1]).await;
+        Timer::after(Duration::from_secs(1)).await;
+    }
+}
+
+pub struct HD44780<'l> {
+    dma: PeripheralRef<'l, AnyChannel>,
+    sm: PioStateMachineInstance<PioInstanceBase<0>, SmInstanceBase<0>>,
+
+    buf: [u8; 40],
+}
+
+impl<'l> HD44780<'l> {
+    pub async fn new(
+        pio: PIO0,
+        dma: impl Peripheral<P = impl Channel> + 'l,
+        rs: impl Pin,
+        rw: impl Pin,
+        e: impl Pin,
+        db4: impl Pin,
+        db5: impl Pin,
+        db6: impl Pin,
+        db7: impl Pin,
+    ) -> HD44780<'l> {
+        into_ref!(dma);
+
+        let db7pin = db7.pin();
+        let (mut common, mut sm0, ..) = pio.split();
+
+        // takes command words (<wait:24> <command:4> <0:4>)
+        let prg = pio_proc::pio_asm!(
+            r#"
+                .side_set 1 opt
+
+                loop:
+                    out x,     24
+                delay:
+                    jmp x--,   delay
+                    out pins,  4     side 1
+                    out null,  4     side 0
+                    jmp !osre, loop
+                irq 0
+            "#,
+        );
+
+        let rs = common.make_pio_pin(rs);
+        let rw = common.make_pio_pin(rw);
+        let e = common.make_pio_pin(e);
+        let db4 = common.make_pio_pin(db4);
+        let db5 = common.make_pio_pin(db5);
+        let db6 = common.make_pio_pin(db6);
+        let db7 = common.make_pio_pin(db7);
+
+        sm0.set_set_pins(&[&rs, &rw]);
+        embassy_rp::pio_instr_util::set_pindir(&mut sm0, 0b11);
+        sm0.set_set_pins(&[&e]);
+        embassy_rp::pio_instr_util::set_pindir(&mut sm0, 0b1);
+        sm0.set_set_pins(&[&db4, &db5, &db6, &db7]);
+        embassy_rp::pio_instr_util::set_pindir(&mut sm0, 0b11111);
+
+        let relocated = RelocatedProgram::new(&prg.program);
+        common.write_instr(relocated.origin() as usize, relocated.code());
+        embassy_rp::pio_instr_util::exec_jmp(&mut sm0, relocated.origin());
+        sm0.set_clkdiv(125 * 256);
+        let pio::Wrap { source, target } = relocated.wrap();
+        sm0.set_wrap(source, target);
+        sm0.set_side_enable(true);
+        sm0.set_out_pins(&[&db4, &db5, &db6, &db7]);
+        sm0.set_sideset_base_pin(&e);
+        sm0.set_sideset_count(2);
+        sm0.set_out_shift_dir(ShiftDirection::Left);
+        sm0.set_fifo_join(FifoJoin::TxOnly);
+        sm0.set_autopull(true);
+        sm0.set_pull_threshold(32);
+
+        sm0.set_enable(true);
+        // init to 8 bit thrice
+        sm0.push_tx((50000 << 8) | 0x30);
+        sm0.push_tx((5000 << 8) | 0x30);
+        sm0.push_tx((200 << 8) | 0x30);
+        // init 4 bit
+        sm0.push_tx((200 << 8) | 0x20);
+        // set font and lines
+        sm0.push_tx((50 << 8) | 0x20);
+        sm0.push_tx(0b1100_0000);
+
+        sm0.wait_irq(0).await;
+        sm0.set_enable(false);
+
+        // takes command sequences (<rs:1> <count:7>, data...)
+        // many side sets are only there to free up a delay bit!
+        let prg = pio_proc::pio_asm!(
+            r#"
+                .origin 7
+                .side_set 1
+
+                .wrap_target
+                pull     side 0
+                out  x 1 side 0 ; !rs
+                out  y 7 side 0 ; #data - 1
+
+                ; rs/rw to e: >= 60ns
+                ; e high time: >= 500ns
+                ; e low time: >= 500ns
+                ; read data valid after e falling: ~5ns
+                ; write data hold after e falling: ~10ns
+
+                loop:
+                    pull                 side 0
+                    jmp  !x       data   side 0
+                command:
+                    set  pins     0b00   side 0
+                    jmp  shift           side 0
+                data:
+                    set  pins     0b01   side 0
+                shift:
+                    out  pins     4      side 1 [9]
+                    nop                  side 0 [9]
+                    out  pins     4      side 1 [9]
+                    mov  osr      null   side 0 [7]
+                    out  pindirs  4      side 0
+                    set  pins     0b10   side 0
+                busy:
+                    nop                  side 1 [9]
+                    jmp  pin      more   side 0 [9]
+                    mov  osr      ~osr   side 1 [9]
+                    nop                  side 0 [4]
+                    out  pindirs  4      side 0
+                    jmp  y--      loop   side 0
+                .wrap
+                more:
+                    nop                  side 1 [9]
+                    jmp busy             side 0 [9]
+            "#
+        );
+
+        let relocated = RelocatedProgram::new(&prg.program);
+        common.write_instr(relocated.origin() as usize, relocated.code());
+        embassy_rp::pio_instr_util::exec_jmp(&mut sm0, relocated.origin());
+        let pio::Wrap { source, target } = relocated.wrap();
+        sm0.set_clkdiv(8 * 256); // ~64ns/insn
+        sm0.set_side_enable(false);
+        sm0.set_jmp_pin(db7pin);
+        sm0.set_wrap(source, target);
+        sm0.set_set_pins(&[&rs, &rw]);
+        sm0.set_out_pins(&[&db4, &db5, &db6, &db7]);
+        sm0.set_sideset_base_pin(&e);
+        sm0.set_sideset_count(1);
+        sm0.set_out_shift_dir(ShiftDirection::Left);
+        sm0.set_fifo_join(FifoJoin::TxOnly);
+
+        sm0.set_enable(true);
+
+        // display on and cursor on and blinking, reset display
+        sm0.dma_push(dma.reborrow(), &[0x81u8, 0x0f, 1]).await;
+
+        Self {
+            dma: dma.map_into(),
+            sm: sm0,
+            buf: [0x20; 40],
+        }
+    }
+
+    pub async fn add_line(&mut self, s: &[u8]) {
+        // move cursor to 0:0, prepare 16 characters
+        self.buf[..3].copy_from_slice(&[0x80, 0x80, 15]);
+        // move line 2 up
+        self.buf.copy_within(22..38, 3);
+        // move cursor to 1:0, prepare 16 characters
+        self.buf[19..22].copy_from_slice(&[0x80, 0xc0, 15]);
+        // file line 2 with spaces
+        self.buf[22..38].fill(0x20);
+        // copy input line
+        let len = s.len().min(16);
+        self.buf[22..22 + len].copy_from_slice(&s[0..len]);
+        // set cursor to 1:15
+        self.buf[38..].copy_from_slice(&[0x80, 0xcf]);
+
+        self.sm.dma_push(self.dma.reborrow(), &self.buf).await;
+    }
+}