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Albeit with no BIOS present, execute.

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This commit is contained in:
Thomas Harte 2023-11-15 16:10:37 -05:00
parent 3b84299a05
commit 2bc9dfbef9
1 changed files with 33 additions and 1 deletions
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34
Machines/PCCompatible/PCCompatible.cpp
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@ -205,6 +205,18 @@ struct Memory {
*reinterpret_cast<uint16_t *>(&memory[target]) = value;
}
//
// Helper for instruction fetch.
//
std::pair<const uint8_t *, size_t> next_code() {
const uint32_t start = segments_.cs_base_ + registers_.ip();
return std::make_pair(&memory[start], 0x10'000 - start);
}
std::pair<const uint8_t *, size_t> all() {
return std::make_pair(memory.data(), 0x10'000);
}
private:
std::vector<uint8_t> memory;
Registers &registers_;
@ -314,8 +326,27 @@ class ConcreteMachine:
void run_for([[maybe_unused]] const Cycles cycles) override {
auto instructions = cycles.as_integral();
while(instructions--) {
// const auto decoded = decoder.decode(data.data(), data.size());
// Get the next thing to execute into decoded.
if(!context.flow_controller.should_repeat()) {
// Decode from the current IP.
const auto remainder = context.memory.next_code();
decoded = decoder.decode(remainder.first, remainder.second);
// If that didn't yield a whole instruction then the end of memory must have been hit;
// continue from the beginning.
if(decoded.first <= 0) {
const auto all = context.memory.all();
decoded = decoder.decode(all.first, all.second);
}
} else {
context.flow_controller.begin_instruction();
}
// Execute it.
InstructionSet::x86::perform(
decoded.second,
context
);
}
}
@ -349,6 +380,7 @@ class ConcreteMachine:
static constexpr auto model = InstructionSet::x86::Model::i8086;
} context;
InstructionSet::x86::Decoder<Context::model> decoder;
std::pair<int, InstructionSet::x86::Instruction<false>> decoded;
};