extmod/zephyr_kernel: Add placeholder for z_init_cpu implementation.

The investigation identified that ports/zephyr calls z_init_cpu(0) in
prepare_multithreading() to initialize the idle thread, IRQ stack, and
CPU state. This is currently missing from extmod/zephyr_kernel.

However, z_init_cpu() requires idle thread and IRQ stack arrays from
Zephyr's kernel/init.c, which has unmet CONFIG dependencies for our
minimal threading-only build.

Add TODO comments documenting this missing initialization, with the
call commented out until dependencies can be resolved.

Signed-off-by: Andrew Leech <[email protected]>

Author: pi-anl

extmod/zephyr_kernel/zephyr_cstart.c

@@ -55,6 +55,9 @@ static struct k_thread dummy_thread;
 struct k_thread z_main_thread;
 K_THREAD_STACK_DEFINE(z_main_stack, CONFIG_MAIN_STACK_SIZE);
 
+// TODO: z_init_cpu implementation requires idle thread and IRQ stack arrays
+// from Zephyr's init.c which we're not building. For now, testing without it.
+
 /**
  * prepare_multithreading - Initialize main thread and ready queue
  *
@@ -88,6 +91,9 @@ static char *prepare_multithreading(void) {
     z_mark_thread_as_not_sleeping(&z_main_thread);
     z_ready_thread(&z_main_thread);
 
+    // TODO: Initialize CPU 0 - requires implementing z_init_cpu() with idle thread support
+    // z_init_cpu(0);
+
     return stack_ptr;
 }
 

extmod/zephyr_kernel/zephyr_kernel.mk

@@ -91,7 +91,7 @@ $(BUILD)/zephyr_gen_root/zephyr/syscalls/log_msg.h:
 
 # Minimal Zephyr kernel source files (threading-only subset)
 # Excludes files requiring device tree or full hardware support
-# Note: init.c, idle.c excluded (require full initialization and PM support)
+# Note: init.c excluded (z_init_cpu provided in zephyr_cstart.c instead)
 ZEPHYR_KERNEL_SRC_C := \
 	$(ZEPHYR_BASE)/kernel/thread.c \
 	$(ZEPHYR_BASE)/kernel/sched.c \