#include <cstring>

#include "arm_defs.hpp"
#include "kernel.hpp"

/*
	This file sets up an idle thread that's meant to run when no other OS thread can run.
	It simply idles and constantly yields to check if there's any other thread that can run
	The code for our idle thread looks like this

idle_thread_main:
	// Sleep for 0 seconds with the SleepThread SVC, which just yields execution
	mov r0, #0
	mov r1, #0
	svc SleepThread

	b idle_thread_main
*/

using namespace KernelMemoryTypes;

static constexpr u8 idleThreadCode[] = {
	0x00, 0x00, 0xA0, 0xE3,  // mov r0, #0
	0x00, 0x10, 0xA0, 0xE3,  // mov r1, #0
	0x0A, 0x00, 0x00, 0xEF,  // svc SleepThread
	0xFB, 0xFF, 0xFF, 0xEA   // b idle_thread_main
};

// Set up an idle thread to run when no thread is able to run
void Kernel::setupIdleThread() {
	Thread& t = threads[idleThreadIndex];

	// Reserve some memory for the idle thread's code. We map this memory to vaddr 3FC00000 which shouldn't be accessed by applications
	// We only allocate 4KB (1 page) because our idle code is pretty small
	constexpr u32 codeAddress = 0x3FC00000;
	if (!mem.allocMemory(codeAddress, 1, FcramRegion::Base, true, true, false, MemoryState::Locked)) {
		Helpers::panic("Failed to setup idle thread");
	}

	// Copy idle thread code to the allocated FCRAM
	mem.copyToVaddr(codeAddress, idleThreadCode, sizeof(idleThreadCode));

	t.entrypoint = codeAddress;
	t.initialSP = 0;
	t.tlsBase = 0;
	t.gprs[13] = 0;  // Set SP & LR to 0 just in case. The idle thread should never access memory, but let's be safe
	t.gprs[14] = 0;
	t.gprs[15] = codeAddress;
	t.cpsr = CPSR::UserMode;
	t.fpscr = FPSCR::ThreadDefault;

	// Our idle thread should have as low of a priority as possible, because, well, it's an idle thread.
	// We handle this by giving it a priority of 0x40, which is lower than is actually allowed for user threads
	// (High priority value = low priority). This is the same priority used in the retail kernel.
	t.priority = 0x40;
	t.status = ThreadStatus::Ready;

	// Add idle thread to the list of thread indices
	threadIndices.push_back(idleThreadIndex);
	sortThreads();
}