add transmit-only UART example

crates/fayalite/examples/tx_only_uart.rs

@@ -0,0 +1,188 @@
+// SPDX-License-Identifier: LGPL-3.0-or-later
+// See Notices.txt for copyright information
+use clap::builder::TypedValueParser;
+use fayalite::{
+    build::{ToArgs, WriteArgs},
+    platform::PeripheralRef,
+    prelude::*,
+};
+use ordered_float::NotNan;
+
+fn pick_clock<'a>(
+    platform_io_builder: &PlatformIOBuilder<'a>,
+) -> PeripheralRef<'a, peripherals::ClockInput> {
+    let mut clks = platform_io_builder.peripherals_with_type::<peripherals::ClockInput>();
+    clks.sort_by_key(|clk| {
+        // sort clocks by preference, smaller return values means higher preference
+        let mut frequency = clk.ty().frequency();
+        let priority;
+        if frequency < 10e6 {
+            frequency = -frequency; // prefer bigger frequencies
+            priority = 1;
+        } else if frequency > 50e6 {
+            // prefer smaller frequencies
+            priority = 2; // least preferred
+        } else {
+            priority = 0; // most preferred
+            frequency = (frequency - 25e6).abs(); // prefer closer to 25MHz
+        }
+        (priority, NotNan::new(frequency).expect("should be valid"))
+    });
+    clks[0]
+}
+
+#[hdl_module]
+fn tx_only_uart(
+    platform_io_builder: PlatformIOBuilder<'_>,
+    divisor: f64,
+    message: impl AsRef<[u8]>,
+) {
+    let message = message.as_ref();
+    let clk_input = pick_clock(&platform_io_builder).use_peripheral();
+    let rst = platform_io_builder.peripherals_with_type::<Reset>()[0].use_peripheral();
+    let cd = #[hdl]
+    ClockDomain {
+        clk: clk_input.clk,
+        rst,
+    };
+    let numerator = 1u128 << 16;
+    let denominator = (divisor * numerator as f64).round() as u128;
+
+    #[hdl]
+    let remainder_reg: UInt<128> = reg_builder().clock_domain(cd).reset(0u128);
+
+    #[hdl]
+    let sum: UInt<128> = wire();
+    connect_any(sum, remainder_reg + numerator);
+
+    #[hdl]
+    let tick_reg = reg_builder().clock_domain(cd).reset(false);
+    connect(tick_reg, false);
+
+    #[hdl]
+    let next_remainder: UInt<128> = wire();
+    connect(remainder_reg, next_remainder);
+
+    #[hdl]
+    if sum.cmp_ge(denominator) {
+        connect_any(next_remainder, sum - denominator);
+        connect(tick_reg, true);
+    } else {
+        connect(next_remainder, sum);
+    }
+
+    #[hdl]
+    let uart_state_reg = reg_builder().clock_domain(cd).reset(0_hdl_u4);
+    #[hdl]
+    let next_uart_state: UInt<4> = wire();
+
+    connect_any(next_uart_state, uart_state_reg + 1u8);
+
+    #[hdl]
+    let message_mem: Array<UInt<8>> = wire(Array[UInt::new_static()][message.len()]);
+    for (message, message_mem) in message.iter().zip(message_mem) {
+        connect(message_mem, *message);
+    }
+    #[hdl]
+    let addr_reg: UInt<32> = reg_builder().clock_domain(cd).reset(0u32);
+    #[hdl]
+    let next_addr: UInt<32> = wire();
+    connect(next_addr, addr_reg);
+
+    #[hdl]
+    let tx = reg_builder().clock_domain(cd).reset(true);
+
+    #[hdl]
+    let tx_bits: Array<Bool, 10> = wire();
+
+    connect(tx_bits[0], false); // start bit
+    connect(tx_bits[9], true); // stop bit
+
+    for i in 0..8 {
+        connect(tx_bits[i + 1], message_mem[addr_reg][i]); // data bits
+    }
+
+    connect(tx, tx_bits[uart_state_reg]);
+
+    #[hdl]
+    if uart_state_reg.cmp_eq(Expr::ty(tx_bits).len() - 1) {
+        connect(next_uart_state, 0_hdl_u4);
+        let next_addr_val = addr_reg + 1u8;
+        #[hdl]
+        if next_addr_val.cmp_lt(message.len()) {
+            connect_any(next_addr, next_addr_val);
+        } else {
+            connect(next_addr, 0u32);
+        }
+    }
+
+    #[hdl]
+    if tick_reg {
+        connect(uart_state_reg, next_uart_state);
+        connect(addr_reg, next_addr);
+    }
+
+    for uart in platform_io_builder.peripherals_with_type::<peripherals::Uart>() {
+        connect(uart.use_peripheral().tx, tx);
+    }
+
+    #[hdl]
+    let io = m.add_platform_io(platform_io_builder);
+}
+
+fn parse_baud_rate(
+    v: impl AsRef<str>,
+) -> Result<NotNan<f64>, Box<dyn std::error::Error + Send + Sync>> {
+    let retval: NotNan<f64> = v
+        .as_ref()
+        .parse()
+        .map_err(|_| "invalid baud rate, must be a finite positive floating-point value")?;
+    if *retval > 0.0 && retval.is_finite() {
+        Ok(retval)
+    } else {
+        Err("baud rate must be finite and positive".into())
+    }
+}
+
+#[derive(Clone, PartialEq, Eq, Hash, Debug, clap::Args)]
+pub struct ExtraArgs {
+    #[arg(long, value_parser = clap::builder::StringValueParser::new().try_map(parse_baud_rate), default_value = "115200")]
+    pub baud_rate: NotNan<f64>,
+    #[arg(long, default_value = "Hello World from Fayalite!!!\r\n", value_parser = clap::builder::NonEmptyStringValueParser::new())]
+    pub message: String,
+}
+
+impl ToArgs for ExtraArgs {
+    fn to_args(&self, args: &mut (impl WriteArgs + ?Sized)) {
+        let Self { baud_rate, message } = self;
+        args.write_display_arg(format_args!("--baud-rate={baud_rate}"));
+        args.write_long_option_eq("message", message);
+    }
+}
+
+fn main() {
+    type Cli = BuildCli<ExtraArgs>;
+    Cli::main(
+        "tx_only_uart",
+        |_, platform, ExtraArgs { baud_rate, message }| {
+            Ok(JobParams::new(platform.try_wrap_main_module(|io| {
+                let clk = pick_clock(&io).ty();
+                let divisor = clk.frequency() / *baud_rate;
+                let baud_rate_error = |msg| {
+                    <Cli as clap::CommandFactory>::command()
+                        .error(clap::error::ErrorKind::ValueValidation, msg)
+                };
+                const HUGE_DIVISOR: f64 = u64::MAX as f64;
+                match divisor {
+                    divisor if !divisor.is_finite() => {
+                        return Err(baud_rate_error("bad baud rate"));
+                    }
+                    HUGE_DIVISOR.. => return Err(baud_rate_error("baud rate is too small")),
+                    4.0.. => {}
+                    _ => return Err(baud_rate_error("baud rate is too large")),
+                }
+                Ok(tx_only_uart(io, divisor, message))
+            })?))
+        },
+    );
+}

crates/fayalite/src/platform/peripherals.rs

@@ -50,3 +50,13 @@ pub struct RgbLed {
     pub g: Bool,
     pub b: Bool,
 }
+
+#[hdl]
+/// UART, used as an output from the FPGA
+pub struct Uart {
+    /// transmit from the FPGA's perspective
+    pub tx: Bool,
+    /// receive from the FPGA's perspective
+    #[hdl(flip)]
+    pub rx: Bool,
+}

crates/fayalite/src/vendor/xilinx/arty_a7.rs

@@ -7,7 +7,7 @@ use crate::{
     platform::{
         DynPlatform, Peripheral, PeripheralRef, Peripherals, PeripheralsBuilderFactory,
         PeripheralsBuilderFinished, Platform, PlatformAspectSet,
-        peripherals::{ClockInput, Led, RgbLed},
+        peripherals::{ClockInput, Led, RgbLed, Uart},
     },
     prelude::*,
     vendor::xilinx::{
@@ -77,6 +77,7 @@ pub struct ArtyA7Peripherals {
     ld5: Peripheral<Led>,
     ld6: Peripheral<Led>,
     ld7: Peripheral<Led>,
+    uart: Peripheral<Uart>,
     // TODO: add rest of peripherals when we need them
 }
 
@@ -94,6 +95,7 @@ impl Peripherals for ArtyA7Peripherals {
             ld5,
             ld6,
             ld7,
+            uart,
         } = self;
         clk100_div_pow2.append_peripherals(peripherals);
         rst.append_peripherals(peripherals);
@@ -106,6 +108,7 @@ impl Peripherals for ArtyA7Peripherals {
         ld5.append_peripherals(peripherals);
         ld6.append_peripherals(peripherals);
         ld7.append_peripherals(peripherals);
+        uart.append_peripherals(peripherals);
     }
 }
 
@@ -192,6 +195,7 @@ impl Platform for ArtyA7Platform {
                 ld5: builder.output_peripheral("ld5", Led),
                 ld6: builder.output_peripheral("ld6", Led),
                 ld7: builder.output_peripheral("ld7", Led),
+                uart: builder.output_peripheral("uart", Uart),
             },
             builder.finish(),
         )
@@ -214,6 +218,7 @@ impl Platform for ArtyA7Platform {
             ld5,
             ld6,
             ld7,
+            uart,
         } = peripherals;
         let make_buffered_input = |name: &str, location: &str, io_standard: &str, invert: bool| {
             let pin = m.input_with_loc(name, SourceLocation::builtin(), Bool);
@@ -373,6 +378,14 @@ impl Platform for ArtyA7Platform {
                 connect(o, false);
             }
         }
+        let uart_tx = make_buffered_output("uart_tx", "D10", "LVCMOS33");
+        let uart_rx = make_buffered_input("uart_rx", "A9", "LVCMOS33", false);
+        if let Some(uart) = uart.into_used() {
+            connect(uart_tx, uart.instance_io_field().tx);
+            connect(uart.instance_io_field().rx, uart_rx);
+        } else {
+            connect(uart_tx, true); // idle
+        }
     }
 
     fn aspects(&self) -> PlatformAspectSet {