Add POC Rust Crazyflie app example

Makefile

@@ -38,6 +38,7 @@ PROCESSOR = -mcpu=cortex-m4 -mthumb -mfloat-abi=hard -mfpu=fpv4-sp-d16
 LINKER_DIR = $(srctree)/tools/make/F405/linker
 
 LDFLAGS += --specs=nosys.specs --specs=nano.specs $(PROCESSOR) -nostdlib
+image_LDFLAGS += -z noexecstack
 image_LDFLAGS += -Wl,-Map=$(PROG).map,--cref,--gc-sections,--undefined=uxTopUsedPriority
 image_LDFLAGS += -L$(srctree)/tools/make/F405/linker
 image_LDFLAGS += -T $(LINKER_DIR)/FLASH_CLOAD.ld

examples/app_hello_rs/.gitignore

@@ -0,0 +1 @@
+target/

examples/app_hello_rs/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "cfapprs"
+version = "0.1.0"
+authors = ["Arnaud Taffanel <[email protected]>"]
+edition = "2021"
+
+[lib]
+crate-type = ["staticlib"]
+
+[dependencies]
+panic-halt = "1.0.0"

examples/app_hello_rs/Kbuild

@@ -0,0 +1,15 @@
+# Name of the RUST lib crate to include in the build
+CRATE_NAME := cfapprs
+
+# The crate's output lib will become app.o to make KBUILD happy 
+obj-y += app.o
+
+# Flag required to link the whole static library into built-in.o, noexecstack matches the default behavior of LLVM
+EXTRA_LDFLAGS += -Wl,--whole-archive -z noexecstack
+
+# Always build the Rust lib crate and copy it to app.o
+$(obj)/app.o: FORCE
+	cargo build --release --target thumbv7em-none-eabihf
+	cp $(obj)/target/thumbv7em-none-eabihf/release/lib$(CRATE_NAME).a $@
+
+FORCE:

examples/app_hello_rs/Makefile

@@ -0,0 +1,23 @@
+# The firmware uses the Kbuild build system. There are 'Kbuild' files in this
+# example that outlays what needs to be built. (check src/Kbuild).
+#
+# The firmware is configured using options in Kconfig files, the
+# values of these end up in the .config file in the firmware directory.
+#
+# By setting the OOT_CONFIG (it is '$(PWD)/oot-config' by default) environment
+# variable you can provide a custom configuration. It is important that you
+# enable the app-layer. See app-config in this directory for example.
+
+#
+# We want to execute the main Makefile for the firmware project,
+# it will handle the build for us.
+#
+CRAZYFLIE_BASE := ../..
+
+#
+# We override the default OOT_CONFIG here, we could also name our config
+# to oot-config and that would be the default.
+#
+OOT_CONFIG := $(PWD)/app-config
+
+include $(CRAZYFLIE_BASE)/tools/make/oot.mk

examples/app_hello_rs/README.md

@@ -0,0 +1,28 @@
+# Rust Hello world App for Crazyflie 2.x
+
+Rust version of the Hello-world app.
+
+This folder shows a proof of concept of how to compile some Rust in the Crazyflie to call firmware functions.
+
+This is a very minimal examples that can be used as a starting point to build better Rust integration for the Crazyflie fiwmware.
+
+## Build dependencies
+
+The prerequisite to build the rust app is to have a recent rust compiler (tested with 1.82.0) and the target for the Crazyflie CPU.
+To install the target with [rustup](https://rustup.rs):
+```
+rustup target add thumbv7em-none-eabihf
+```
+
+## Architecture
+
+The Crazyflie build system is based on KBuild and it had to be creatively bent to allow to link a static library.
+This is done my renaming the Rust crate output static lib into a .o and make sure GCC copies the full lib content into the resulting firmware (See [Kbuild](Kbuild)).
+
+The Rust project is setup to generate a C static library.
+The Makefile calls `cargo build` to build the lib and copies the resulting lib into ```app.o```.
+
+The Crazyflie firmware will call `appMain()` at startup.
+This function is declared in rust as `pub extern "C"` to be callable from C.
+
+The FreeRTOS delay function and Crazyflie console putchar function are manually declared `extern "C"` which allows Rust to call them.

examples/app_hello_rs/app-config

@@ -0,0 +1,3 @@
+CONFIG_APP_ENABLE=y
+CONFIG_APP_PRIORITY=1
+CONFIG_APP_STACKSIZE=350

examples/app_hello_rs/src/lib.rs

@@ -0,0 +1,23 @@
+#![no_std]
+
+use panic_halt as _;
+
+extern "C" {
+    pub fn vTaskDelay(ticks: u32);
+    pub fn consolePutchar(ch: i32) -> i32;
+}
+
+fn console_print(msg: &str) {
+    for c in msg.as_bytes() {
+        unsafe{ consolePutchar(*c as i32); }
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn appMain() -> i32 {
+    console_print("Hello from Rust!\n");
+
+    loop {
+        unsafe { vTaskDelay(1000); }
+    }
+}