More revisions to Zephyr doc

Author: xtremekforever

Sources/EmbeddedSwift/Documentation.docc/SDKSupport/IntegrateWithZephyr.md

@@ -31,26 +31,27 @@ Refer to the [Zephyr Releases](https://docs.zephyrproject.org/latest/releases/in
 
 ## Project Setup
 
-Once Zephyr is setup, the next step is to setup a project with a bridging header, `CMakeLists.txt`, `Main.swift`, and `prj.conf`:
+Once Zephyr is setup, the next step is to setup a project with the following files included:
 
 ```plain
-SwiftZephyrProject/BridgingHeader.h
+SwiftZephyrProject/src/BridgingHeader.h
+SwiftZephyrProject/src/Main.swift
+SwiftZephyrProject/src/Stubs.c
 SwiftZephyrProject/CMakeLists.txt
-SwiftZephyrProject/Main.swift
 SwiftZephyrProject/prj.conf
 ```
 
-These are the minimum required files in order to build a Zephyr project. For example, `prj.conf` is required even if it is empty, or the project will not build.
+These are the minimum required files in order to build a Zephyr project. By convention, source files should be placed in the src/ subdirectory, but this is not a hard requirement. Also, `prj.conf` is required even if it is empty, or the project will not build.
 
-Inside of `BridgingHeader.h`, add the following content as a minimum:
+Inside of `src/BridgingHeader.h`, add the following content as a minimum:
 
 ```c
 #pragma once
 
 #include <autoconf.h>
 ```
 
-The `Main.swift` file must contain a `static func main()` as follows:
+The `src/Main.swift` file must contain a `static func main()` as follows:
 
 ```swift
 @main
@@ -61,6 +62,30 @@ struct Main {
 }
 ```
 
+Since Embedded Swift requires posix_memalign to be defined, add the following to `src/Stubs.c` to define it:
+
+```c
+#include <stdlib.h>
+#include <errno.h>
+
+void *aligned_alloc(size_t alignment, size_t size);
+
+// Embedded Swift currently requires posix_memalign, but the C libraries in the
+// Zephyr SDK do not provide it. Let's implement it and forward the calls to
+// aligned_alloc(3).
+int
+posix_memalign(void **memptr, size_t alignment, size_t size)
+{
+  void *p = aligned_alloc(alignment, size);
+  if (p) {
+    *memptr = p;
+    return 0;
+  }
+
+  return errno;
+}
+```
+
 ### CMakeLists.txt Setup
 
 The `CMakeLists.txt` setup is more involved and complex since target, compilation flags, and library linking must be specified for Swift. First, some initial setup and flags:
@@ -69,20 +94,19 @@ The `CMakeLists.txt` setup is more involved and complex since target, compilatio
 cmake_minimum_required(VERSION 3.29)
 find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
 
-# Use the armv7em-none-none-eabi target triple for Swift
-set(CMAKE_Swift_COMPILER_TARGET armv7em-none-none-eabi)
 # Enable "wmo" as needed by Embedded Swift
 set(CMAKE_Swift_COMPILATION_MODE wholemodule)
-# FIXME: Skip checking if the compiler works
-set(CMAKE_Swift_COMPILER_WORKS true)
 
 # Create a new project called "SwiftZephyrProject" and enable "Swift" as a supported language
 project(SwiftZephyrProject Swift)
 ```
 
-The following flags have been curated to work well with `armv7em-none-none-eabi` target with `swiftc`. Some flags may need to change depending on the chosen target:
+The following flags have been curated to work well with the `armv7em-none-none-eabi` target with `swiftc`. Some flags may need to change depending on the chosen target:
 
 ```cmake
+# Use the armv7em-none-none-eabi target triple for Swift
+set(CMAKE_Swift_COMPILER_TARGET armv7em-none-none-eabi)
+
 # Set global Swift compiler flags
 add_compile_options(
     # Enable Embedded Swift
@@ -126,9 +150,11 @@ endif()
 Finally, setup targets, libraries, and additional compile options:
 
 ```cmake
+target_sources(app PRIVATE src/Stubs.c)
+
 # The Swift code providing "main" needs to be in an OBJECT library (instead of STATIC library) to make sure it actually gets linker.
 # A STATIC library would get dropped from linking because Zephyr provides a default weak empty main definition.
-add_library(app_swift OBJECT Main.swift)
+add_library(app_swift OBJECT src/Main.swift)
 
 add_dependencies(app_swift syscall_list_h_target)
 target_compile_options(app_swift PRIVATE
@@ -139,7 +165,7 @@ target_compile_options(app_swift PRIVATE
     -Xfrontend -disable-stack-protector
 
     # FIXME: add dependency on BridgingHeader.h
-    -import-bridging-header ${CMAKE_CURRENT_LIST_DIR}/BridgingHeader.h
+    -import-bridging-header ${CMAKE_CURRENT_LIST_DIR}/src/BridgingHeader.h
 )
 
 # Copy include paths from C target to Swift target