rust: Add a Rust compatible API implementation.

We will gradually add a Rust compatible API implementation conforming
to Apache-2.
This PR adds an alternative implementation of Common.cpp.

Signed-off-by: TOKITA Hiroshi <tokita.hiroshi@gmail.com>

Author: soburi

.gitignore

@@ -0,0 +1 @@
+rust/Cargo.lock

CMakeLists.txt

@@ -10,4 +10,74 @@ if (CONFIG_ARDUINO_API)
   add_subdirectory(cores)
   add_subdirectory(libraries)
   zephyr_include_directories(${variant_dir})
+
+  # quote from https://github.com/zephyrproject-rtos/zephyr-lang-rust/blob/main/CMakeLists.txt
+  function (rust_target_arch RUST_TARGET)
+    # Map Zephyr targets to LLVM targets.
+    if(CONFIG_CPU_CORTEX_M)
+      if(CONFIG_CPU_CORTEX_M0 OR CONFIG_CPU_CORTEX_M0PLUS OR CONFIG_CPU_CORTEX_M1)
+        set(${RUST_TARGET} "thumbv6m-none-eabi" PARENT_SCOPE)
+      elseif(CONFIG_CPU_CORTEX_M3)
+        set(${RUST_TARGET} "thumbv7m-none-eabi" PARENT_SCOPE)
+      elseif(CONFIG_CPU_CORTEX_M4 OR CONFIG_CPU_CORTEX_M7)
+        if(CONFIG_FP_HARDABI OR FORCE_FP_HARDABI)
+          set(${RUST_TARGET} "thumbv7em-none-eabihf" PARENT_SCOPE)
+        else()
+          set(${RUST_TARGET} "thumbv7em-none-eabi" PARENT_SCOPE)
+        endif()
+      elseif(CONFIG_CPU_CORTEX_M23)
+        set(${RUST_TARGET} "thumbv8m.base-none-eabi" PARENT_SCOPE)
+      elseif(CONFIG_CPU_CORTEX_M33 OR CONFIG_CPU_CORTEX_M55)
+        # Not a typo, Zephyr, uses ARMV7_M_ARMV8_M_FP to select the FP even on v8m.
+        if(CONFIG_FP_HARDABI OR FORCE_FP_HARDABI)
+          set(${RUST_TARGET} "thumbv8m.main-none-eabihf" PARENT_SCOPE)
+        else()
+          set(${RUST_TARGET} "thumbv8m.main-none-eabi" PARENT_SCOPE)
+        endif()
+
+        # Todo: The M55 is thumbv8.1m.main-none-eabi, which can be added when Rust
+        # gain support for this target.
+      else()
+        message(FATAL_ERROR "Unknown Cortex-M target.")
+      endif()
+    elseif(CONFIG_RISCV)
+      if(CONFIG_RISCV_ISA_RV64I)
+        # TODO: Should fail if the extensions don't match.
+        set(${RUST_TARGET} "riscv64imac-unknown-none-elf" PARENT_SCOPE)
+      elseif(CONFIG_RISCV_ISA_RV32I)
+        # TODO: We have multiple choices, try to pick the best.
+        set(${RUST_TARGET} "riscv32i-unknown-none-elf" PARENT_SCOPE)
+      else()
+        message(FATAL_ERROR "Rust: Unsupported riscv ISA")
+      endif()
+    elseif(CONFIG_ARCH_POSIX AND CONFIG_64BIT AND (${CMAKE_HOST_SYSTEM_PROCESSOR} MATCHES "x86_64"))
+      set(${RUST_TARGET} "x86_64-unknown-none" PARENT_SCOPE)
+    elseif(CONFIG_ARCH_POSIX AND CONFIG_64BIT AND (${CMAKE_HOST_SYSTEM_PROCESSOR} MATCHES "aarch64"))
+      set(${RUST_TARGET} "aarch64-unknown-none" PARENT_SCOPE)
+    else()
+      message(FATAL_ERROR "Rust: Add support for other target")
+    endif()
+  endfunction()
+
+  rust_target_arch(RUST_TARGET_TRIPLE)
+
+  set(RUST_CRATE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/rust)
+  set(RUST_OUT_DIR   ${CMAKE_CURRENT_BINARY_DIR}/rust)
+  set(RUST_LIB       ${RUST_OUT_DIR}/target/${RUST_TARGET_TRIPLE}/release/libarduinocore_api_rust.a)
+
+  add_custom_command(
+    OUTPUT ${RUST_LIB}
+    COMMAND ${CMAKE_COMMAND} -E env CARGO_TARGET_DIR=${RUST_OUT_DIR}/target
+            cargo build --manifest-path ${RUST_CRATE_DIR}/Cargo.toml
+	    --target ${RUST_TARGET_TRIPLE} --release
+    WORKING_DIRECTORY ${RUST_CRATE_DIR}
+    COMMENT "Building Rust staticlib for ${RUST_TARGET}"
+    VERBATIM
+  )
+
+  add_custom_target(arduinocore_api_rust_build ALL DEPENDS ${RUST_LIB})
+  add_library(arduinocore_api_rust STATIC IMPORTED GLOBAL)
+  set_target_properties(arduinocore_api_rust PROPERTIES IMPORTED_LOCATION ${RUST_LIB})
+  zephyr_link_libraries(arduinocore_api_rust)
+
 endif()

Kconfig

@@ -13,6 +13,7 @@ config ARDUINO_API
 	imply CBPRINTF_FP_SUPPORT
 	imply RING_BUFFER
 	select UART_INTERRUPT_DRIVEN
+	select RUST
 	default n
 
 if ARDUINO_API

cores/arduino/CMakeLists.txt

@@ -7,6 +7,7 @@ if(NOT DEFINED ARDUINO_BUILD_PATH)
 zephyr_sources(zephyrPrint.cpp)
 zephyr_sources(zephyrSerial.cpp)
 zephyr_sources(zephyrCommon.cpp)
+zephyr_sources(apiCommon.cpp)
 
 if(DEFINED CONFIG_ARDUINO_ENTRY)
 zephyr_sources(main.cpp)

cores/arduino/apiCommon.cpp

@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2025 TOKITA Hiroshi
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <Arduino.h>
+#include "zephyrInternal.h"
+
+extern "C" {
+  int32_t map_i32(int32_t x, int32_t in_min, int32_t in_max, int32_t out_min, int32_t out_max);
+  uint16_t makeWord_w(uint16_t w);
+  uint16_t makeWord_hl(byte h, byte l);
+}
+
+long map(long x, long in_min, long in_max, long out_min, long out_max)
+{
+  return map_i32(x, in_min, in_max, out_min, out_max);
+}
+
+uint16_t makeWord(uint16_t w) {
+  return makeWord_w(w);
+}
+uint16_t makeWord(byte h, byte l) {
+  return makeWord_hl(h, l);
+}

rust/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "arduinocore_api_rust"
+version = "0.1.0"
+edition = "2024"
+license = "Apache-2.0"
+
+[lib]
+crate-type = ["staticlib"]

rust/src/common.rs

@@ -0,0 +1,22 @@
+// Copyright (c) 2025 TOKITA Hiroshi
+// SPDX-License-Identifier: Apache-2.0
+
+#[unsafe(no_mangle)]
+pub extern "C" fn map_i32(
+    x: i32, in_min: i32, in_max: i32, out_min: i32, out_max: i32
+) -> i32 {
+    let num = x.wrapping_sub(in_min).wrapping_mul(out_max.wrapping_sub(out_min));
+    let den = in_max.wrapping_sub(in_min);
+    // Note: To keep compatibility, the panic when den=0 is left as is.
+    num / den.wrapping_add(out_min)
+}
+
+#[unsafe(no_mangle)]
+pub extern "C" fn makeWord_w(w: u16) -> u16 {
+    w
+}
+
+#[unsafe(no_mangle)]
+pub extern "C" fn makeWord_hl(h: u8, l: u8) -> u16 {
+    ((h as u16) << 8) | (l as u16)
+}

rust/src/lib.rs

@@ -0,0 +1,14 @@
+// Copyright (c) 2025 TOKITA Hiroshi
+// SPDX-License-Identifier: Apache-2.0
+
+#![no_std]
+
+mod common;
+pub use common::*;
+
+use core::panic::PanicInfo;
+
+#[panic_handler]
+fn panic(_panic: &PanicInfo<'_>) -> ! {
+    loop {}
+}