Add rust package embedded-std with module string

Having our own std library with newtypes allows us to implement
traits of `ufmt`.

firmware-support/Cargo.toml

@@ -1,9 +1,10 @@
-# SPDX-FileCopyrightText: 2022 Google LLC
+# SPDX-FileCopyrightText: 2022-2024 Google LLC
 #
 # SPDX-License-Identifier: CC0-1.0
 
 [workspace]
 members = [
   "bittide-sys",
+  "embedded-std",
 ]
 resolver = "2"

firmware-support/embedded-std/Cargo.toml

@@ -0,0 +1,30 @@
+# SPDX-FileCopyrightText: 2024 Google LLC
+#
+# SPDX-License-Identifier: CC0-1.0
+
+[package]
+name = "embedded-std"
+version = "0.1.0"
+edition = "2021"
+license = "Apache-2.0"
+authors = ["Google LLC"]
+resolver = "2"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[features]
+panic-handler = []
+default = []
+
+[dependencies]
+ufmt = "0.2.0"
+heapless = { version = "0.7", default-features = false}
+
+[dev-dependencies]
+proptest = "1.0"
+object = { version = "0.28", features = ["write"] }
+libc = "0.2"
+test-strategy = "0.2.0"
+rand = "0.8"
+lazy_static = "1.0"
+tempfile = "3"

firmware-support/embedded-std/src/lib.rs

@@ -0,0 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Google LLC
+//
+// SPDX-License-Identifier: Apache-2.0
+
+#![no_std]
+
+pub mod string;

firmware-support/embedded-std/src/string.rs

@@ -0,0 +1,31 @@
+// SPDX-FileCopyrightText: 2024 Google LLC
+//
+// SPDX-License-Identifier: Apache-2.0
+use ufmt::{uDisplay, uWrite};
+
+#[derive(Clone)]
+pub struct String<const SIZE: usize>(pub heapless::String<SIZE>);
+
+impl <const SIZE: usize> String<SIZE> {
+    pub fn new() -> Self {
+        String(heapless::String::new())
+    }
+}
+
+impl<const SIZE: usize> uDisplay for String<SIZE> {
+    #[inline(always)]
+    fn fmt<W>(&self, f: &mut ufmt::Formatter<'_, W>) -> Result<(), W::Error>
+    where
+        W: uWrite + ?Sized,
+    {
+        f.write_str(&self.0.as_str())
+    }
+}
+
+impl <const SIZE: usize>  ufmt::uWrite for String<SIZE> {
+    fn write_str(&mut self, s: &str) -> Result<(), Self::Error> {
+        self.0.push_str(s)?;
+        Ok(())
+    }
+    type Error = ();
+}