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Add timers.

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This commit is contained in:
Thomas Harte 2024-12-10 18:04:10 -05:00
parent ab2a576e1b
commit 6b7edac6e4
1 changed files with 104 additions and 3 deletions
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107
Machines/Commodore/Plus4/Plus4.cpp
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@ -53,6 +53,73 @@ private:
static constexpr auto Shift = ln2(PageSize);
};
class Timers {
public:
template <int offset>
void write(const uint8_t value) {
const auto load_low = [&](uint16_t &target) {
target = uint16_t((target & 0xff00) | (value << 0));
};
const auto load_high = [&](uint16_t &target) {
target = uint16_t((target & 0x00ff) | (value << 8));
};
constexpr auto timer = offset >> 1;
paused_[timer] = !(offset & 1);
if constexpr (offset & 1) {
load_high(timers_[timer]);
if(!timer) {
load_high(timer0_reload_);
}
} else {
load_low(timers_[timer]);
if(!timer) {
load_low(timer0_reload_);
}
}
}
template <int offset>
uint8_t read() {
constexpr auto timer = offset >> 1;
if constexpr (offset & 1) {
return uint8_t(timers_[timer] >> 8);
} else {
return uint8_t(timers_[timer] >> 0);
}
}
void tick(int count) {
// Quick hack here; do better than stepping through one at a time.
while(count--) {
decrement<0>();
decrement<1>();
decrement<2>();
}
}
private:
template <int timer>
void decrement() {
if(paused_[timer]) return;
// Check for reload.
if(!timer && !timers_[timer]) {
timers_[timer] = timer0_reload_;
}
-- timers_[timer];
// Check for interrupt.
if(!timers_[timer]) {
}
}
uint16_t timers_[3]{};
uint16_t timer0_reload_ = 0xffff;
bool paused_[3]{};
};
class ConcreteMachine:
public CPU::MOS6502::BusHandler,
public MachineTypes::TimedMachine,
@ -94,7 +161,38 @@ public:
const uint16_t address,
uint8_t *const value
) {
// printf("%04x\n", address);
// TODO: calculate length of this bus operation.
const auto length = Cycles(5);
// Update other subsystems.
// TODO: timers decrement at a 894 KHz rate for NTSC television systems, 884 KHZ for PAL systems.
// Probably a function of the speed register?
timers_subcycles_ += length;
const auto timers_cycles = timers_subcycles_.divide(Cycles(5));
timers_.tick(timers_cycles.as<int>());
// Perform actual access.
if(address >= 0xff00 && address < 0xff40) {
if(isReadOperation(operation)) {
switch(address) {
case 0xff00: *value = timers_.read<0>(); break;
case 0xff01: *value = timers_.read<1>(); break;
case 0xff02: *value = timers_.read<2>(); break;
case 0xff03: *value = timers_.read<3>(); break;
case 0xff04: *value = timers_.read<4>(); break;
case 0xff05: *value = timers_.read<5>(); break;
}
} else {
switch(address) {
case 0xff00: timers_.write<0>(*value); break;
case 0xff01: timers_.write<1>(*value); break;
case 0xff02: timers_.write<2>(*value); break;
case 0xff03: timers_.write<3>(*value); break;
case 0xff04: timers_.write<4>(*value); break;
case 0xff05: timers_.write<5>(*value); break;
}
}
}
if(address >= 0xfd00 && address < 0xff40) {
if(isReadOperation(operation)) {
@ -102,7 +200,7 @@ public:
} else {
printf("TODO: TED write of %02x @ %04x\n", *value, address);
}
return Cycles(5);
return length;
}
if(isReadOperation(operation)) {
@ -111,7 +209,7 @@ public:
map_.write(address) = *value;
}
return Cycles(5);
return length;
}
private:
@ -136,6 +234,9 @@ private:
std::array<uint8_t, 65536> ram_;
std::vector<uint8_t> kernel_;
std::vector<uint8_t> basic_;
Cycles timers_subcycles_;
Timers timers_;
};
}