add no_std program and build it in github actions

Author: RCasatta

.github/workflows/embedded.yml

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+name: Test Embedded
+
+on:
+  push:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v2
+      - name: Checkout Toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          override: true
+          components: rust-src
+          target: thumbv7m-none-eabi
+      -
+        name: Build
+        run: cd embedded && cargo build

embedded/.cargo/config

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+[target.thumbv7m-none-eabi]
+# uncomment this to make `cargo run` execute programs on QEMU
+runner = "qemu-system-arm -cpu cortex-m3 -machine lm3s6965evb -nographic -semihosting-config enable=on,target=native -kernel"
+
+rustflags = [
+  # This is needed if your flash or ram addresses are not aligned to 0x10000 in memory.x
+  # See https://github.com/rust-embedded/cortex-m-quickstart/pull/95
+  "-C", "link-arg=--nmagic",
+
+  # LLD (shipped with the Rust toolchain) is used as the default linker
+  "-C", "link-arg=-Tlink.x",
+
+  # if you run into problems with LLD switch to the GNU linker by commenting out
+  # this line
+  # "-C", "linker=arm-none-eabi-ld",
+
+  # if you need to link to pre-compiled C libraries provided by a C toolchain
+  # use GCC as the linker by commenting out both lines above and then
+  # uncommenting the three lines below
+  # "-C", "linker=arm-none-eabi-gcc",
+  # "-C", "link-arg=-Wl,-Tlink.x",
+  # "-C", "link-arg=-nostartfiles",
+]
+
+[build]
+target = "thumbv7m-none-eabi"        # Cortex-M3

embedded/Cargo.toml

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+[package]
+authors = ["Riccardo Casatta <[email protected]>"]
+edition = "2018"
+readme = "README.md"
+name = "embedded"
+version = "0.1.0"
+
+[dependencies]
+cortex-m = "0.6.0"
+cortex-m-rt = "0.6.10"
+cortex-m-semihosting = "0.3.3"
+panic-halt = "0.2.0"
+bitcoin_hashes = { path="../", default-features = false }
+
+# Uncomment for the panic example.
+# panic-itm = "0.4.1"
+
+# Uncomment for the allocator example.
+# alloc-cortex-m = "0.4.0"
+
+# Uncomment for the device example.
+# Update `memory.x`, set target to `thumbv7em-none-eabihf` in `.cargo/config`,
+# and then use `cargo build --examples device` to build it.
+# [dependencies.stm32f3]
+# features = ["stm32f303", "rt"]
+# version = "0.7.1"
+
+# this lets you use `cargo fix`!
+[[bin]]
+name = "embedded"
+test = false
+bench = false
+
+[profile.release]
+codegen-units = 1 # better optimizations
+debug = true # symbols are nice and they don't increase the size on Flash
+lto = true # better optimizations

embedded/build.rs

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+//! This build script copies the `memory.x` file from the crate root into
+//! a directory where the linker can always find it at build time.
+//! For many projects this is optional, as the linker always searches the
+//! project root directory -- wherever `Cargo.toml` is. However, if you
+//! are using a workspace or have a more complicated build setup, this
+//! build script becomes required. Additionally, by requesting that
+//! Cargo re-run the build script whenever `memory.x` is changed,
+//! updating `memory.x` ensures a rebuild of the application with the
+//! new memory settings.
+
+use std::env;
+use std::fs::File;
+use std::io::Write;
+use std::path::PathBuf;
+
+fn main() {
+    // Put `memory.x` in our output directory and ensure it's
+    // on the linker search path.
+    let out = &PathBuf::from(env::var_os("OUT_DIR").unwrap());
+    File::create(out.join("memory.x"))
+        .unwrap()
+        .write_all(include_bytes!("memory.x"))
+        .unwrap();
+    println!("cargo:rustc-link-search={}", out.display());
+
+    // By default, Cargo will re-run a build script whenever
+    // any file in the project changes. By specifying `memory.x`
+    // here, we ensure the build script is only re-run when
+    // `memory.x` is changed.
+    println!("cargo:rerun-if-changed=memory.x");
+}

embedded/memory.x

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+MEMORY
+{
+  /* NOTE 1 K = 1 KiBi = 1024 bytes */
+  /* TODO Adjust these memory regions to match your device memory layout */
+  /* These values correspond to the LM3S6965, one of the few devices QEMU can emulate */
+  FLASH : ORIGIN = 0x00000000, LENGTH = 256K
+  RAM : ORIGIN = 0x20000000, LENGTH = 64K
+}
+
+/* This is where the call stack will be allocated. */
+/* The stack is of the full descending type. */
+/* You may want to use this variable to locate the call stack and static
+   variables in different memory regions. Below is shown the default value */
+/* _stack_start = ORIGIN(RAM) + LENGTH(RAM); */
+
+/* You can use this symbol to customize the location of the .text section */
+/* If omitted the .text section will be placed right after the .vector_table
+   section */
+/* This is required only on microcontrollers that store some configuration right
+   after the vector table */
+/* _stext = ORIGIN(FLASH) + 0x400; */
+
+/* Example of putting non-initialized variables into custom RAM locations. */
+/* This assumes you have defined a region RAM2 above, and in the Rust
+   sources added the attribute `#[link_section = ".ram2bss"]` to the data
+   you want to place there. */
+/* Note that the section will not be zero-initialized by the runtime! */
+/* SECTIONS {
+     .ram2bss (NOLOAD) : ALIGN(4) {
+       *(.ram2bss);
+       . = ALIGN(4);
+     } > RAM2
+   } INSERT AFTER .bss;
+*/

embedded/src/main.rs

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+#![no_std]
+#![no_main]
+
+#[macro_use]
+extern crate bitcoin_hashes;
+
+// pick a panicking behavior
+use panic_halt as _; // you can put a breakpoint on `rust_begin_unwind` to catch panics
+// use panic_abort as _; // requires nightly
+// use panic_itm as _; // logs messages over ITM; requires ITM support
+// use panic_semihosting as _; // logs messages to the host stderr; requires a debugger
+
+use cortex_m_rt::entry;
+use cortex_m_semihosting::{debug, hprintln};
+use bitcoin_hashes::sha256;
+use core::str::FromStr;
+use bitcoin_hashes::Hash;
+
+hash_newtype!(TestType, sha256::Hash, 32, doc="test");
+
+#[entry]
+fn main() -> ! {
+    hprintln!("Hello world!").unwrap();
+
+    debug::exit(debug::EXIT_SUCCESS);
+
+    loop {
+        // your code goes here
+    }
+}