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59 lines
2.1 KiB
C++
59 lines
2.1 KiB
C++
#include <cstring>
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#include "arm_defs.hpp"
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#include "kernel.hpp"
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/*
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This file sets up an idle thread that's meant to run when no other OS thread can run.
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It simply idles and constantly yields to check if there's any other thread that can run
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The code for our idle thread looks like this
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idle_thread_main:
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// Sleep for 0 seconds with the SleepThread SVC, which just yields execution
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mov r0, #0
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mov r1, #0
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svc SleepThread
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b idle_thread_main
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*/
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static constexpr u8 idleThreadCode[] = {
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0x00, 0x00, 0xA0, 0xE3, // mov r0, #0
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0x00, 0x10, 0xA0, 0xE3, // mov r1, #0
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0x0A, 0x00, 0x00, 0xEF, // svc SleepThread
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0xFB, 0xFF, 0xFF, 0xEA // b idle_thread_main
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};
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// Set up an idle thread to run when no thread is able to run
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void Kernel::setupIdleThread() {
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Thread& t = threads[idleThreadIndex];
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constexpr u32 codeAddress = 0xBFC00000;
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// Reserve some memory for the idle thread's code. We map this memory to vaddr BFC00000 which is not userland-accessible
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// We only allocate 4KB (1 page) because our idle code is pretty small
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const u32 fcramIndex = mem.allocateSysMemory(Memory::pageSize);
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auto vaddr = mem.allocateMemory(codeAddress, fcramIndex, Memory::pageSize, true, true, false, true, false, true);
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if (!vaddr.has_value() || vaddr.value() != codeAddress) {
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Helpers::panic("Failed to setup idle thread");
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}
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// Copy idle thread code to the allocated FCRAM
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std::memcpy(&mem.getFCRAM()[fcramIndex], idleThreadCode, sizeof(idleThreadCode));
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t.entrypoint = codeAddress;
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t.tlsBase = 0;
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t.gprs[13] = 0; // Set SP & LR to 0 just in case. The idle thread should never access memory, but let's be safe
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t.gprs[14] = 0;
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t.gprs[15] = codeAddress;
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t.cpsr = CPSR::UserMode;
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t.fpscr = FPSCR::ThreadDefault;
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// Our idle thread should have as low of a priority as possible, because, well, it's an idle thread.
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// We handle this by giving it a priority of 0x40, which is lower than is actually allowed for user threads
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// (High priority value = low priority). This is the same priority used in the retail kernel.
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t.priority = 0x40;
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t.status = ThreadStatus::Ready;
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// Add idle thread to the list of thread indices
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threadIndices.push_back(idleThreadIndex);
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sortThreads();
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}
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