Implement a USB serial example

Lifted directly from https://github.com/rp-rs/rp-hal-boards/blob/HEAD/boards/rp-pico/examples/pico_usb_serial.rs.

Cargo.toml

@@ -33,4 +33,4 @@ members = [
     "tree",
     "visions/server",
     "gm-dash/server"
-]
+, "pico-usb-serial"]

pico-usb-serial/.cargo/config

@@ -0,0 +1,12 @@
+[build]
+target = "thumbv6m-none-eabi"
+
+[target.thumbv6m-none-eabi]
+rustflags = [
+    "-C", "link-arg=--nmagic",
+    "-C", "link-arg=-Tlink.x",
+    "-C", "inline-threshold=5",
+    "-C", "no-vectorize-loops",
+]
+
+runner = "elf2uf2-rs -d"

pico-usb-serial/Cargo.toml

@@ -0,0 +1,23 @@
+[package]
+name = "pico-usb-serial"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+# az              = { version = "1" }
+# cortex-m-rt     = { version = "0.7.3" }
+# cortex-m        = { version = "0.7.7" }
+# embedded-alloc  = { version = "0.5.1" }
+# embedded-hal    = { version = "0.2.7" }
+# fixed           = { version = "1" }
+# fugit           = { version = "0.3.7" }
+# panic-halt      = { version = "0.2.0" }
+# rp-pico         = { version = "0.8.0" }
+usb-device = "0.3.2"
+usbd-serial = "0.2.2"
+heapless = "0.8.0"
+rp-pico = "0.9.0"
+embedded-hal = "1.0.0"
+embedded-alloc = "0.6.0"
+cortex-m-rt = "0.7.5"
+panic-halt = "1.0.0"

pico-usb-serial/src/main.rs

@@ -0,0 +1,81 @@
+// Lifted directly from https://github.com/rp-rs/rp-hal-boards/blob/HEAD/boards/rp-pico/examples/pico_usb_serial.rs
+#![no_main]
+#![no_std]
+
+use core::fmt::Write;
+use heapless::String;
+use panic_halt as _;
+use rp_pico::{
+    entry,
+    hal::{self, pac},
+};
+use usb_device::{class_prelude::*, prelude::*};
+use usbd_serial::SerialPort;
+
+#[entry]
+fn main() -> ! {
+    let mut pac = pac::Peripherals::take().unwrap();
+    let mut watchdog = hal::Watchdog::new(pac.WATCHDOG);
+    let clocks = hal::clocks::init_clocks_and_plls(
+        rp_pico::XOSC_CRYSTAL_FREQ,
+        pac.XOSC,
+        pac.CLOCKS,
+        pac.PLL_SYS,
+        pac.PLL_USB,
+        &mut pac.RESETS,
+        &mut watchdog,
+    )
+    .ok()
+    .unwrap();
+
+    let timer = hal::Timer::new(pac.TIMER, &mut pac.RESETS, &clocks);
+
+    let usb_bus = UsbBusAllocator::new(hal::usb::UsbBus::new(
+        pac.USBCTRL_REGS,
+        pac.USBCTRL_DPRAM,
+        clocks.usb_clock,
+        true,
+        &mut pac.RESETS,
+    ));
+
+    let mut serial = SerialPort::new(&usb_bus);
+
+    let mut usb_dev = UsbDeviceBuilder::new(&usb_bus, UsbVidPid(0x16c0, 0x27dd))
+        .strings(&[StringDescriptors::default()
+            .manufacturer("Fake company")
+            .product("Serial port")
+            .serial_number("TEST")])
+        .unwrap()
+        .device_class(2)
+        .build();
+
+    let mut said_hello = false;
+    loop {
+        if !said_hello && timer.get_counter().ticks() >= 2_000_000 {
+            said_hello = true;
+            let _ = serial.write(b"Hello, World!\r\n");
+            let time = timer.get_counter().ticks();
+            let mut text: String<64> = String::new();
+            writeln!(&mut text, "Current timer ticks: {}", time).unwrap();
+            let _ = serial.write(text.as_bytes());
+        }
+
+        if usb_dev.poll(&mut [&mut serial]) {
+            let mut buf = [0u8; 64];
+            match serial.read(&mut buf) {
+                Err(_e) => {}
+                Ok(0) => {}
+                Ok(count) => {
+                    buf.iter_mut().take(count).for_each(|b| { b.make_ascii_uppercase(); });
+                    let mut wr_ptr = &buf[..count];
+                    while !wr_ptr.is_empty() {
+                        match serial.write(wr_ptr) {
+                            Ok(len) => wr_ptr = &wr_ptr[len..],
+                            Err(_) => break,
+                        };
+                    }
+                }
+            }
+        }
+    }
+}