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Handling DMA's modes

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This commit is contained in:
Anonymus Raccoon
2020-05-28 01:17:45 +02:00
parent 291426a392
commit 5ef1ba8d4f
2 changed files with 30 additions and 9 deletions
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35
sources/CPU/DMA/DMA.cpp
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@@ -65,24 +65,24 @@ namespace ComSquare::CPU
}
}
unsigned DMA::_writeOneByte()
unsigned DMA::_writeOneByte(uint24_t aAddress, uint24_t bAddress)
{
// Address $2180 refers to the WRam data register. Write to/Read from this port when the a address is on the vram cause different behaviors.
if (this->port == 0x80) {
auto accessor = this->_bus->getAccessor(this->aAddress.raw);
auto accessor = this->_bus->getAccessor(aAddress);
if (accessor && accessor->getComponent() == WRam) {
if (this->controlRegister.direction == AToB)
return 8;
this->_bus->write(this->aAddress.raw, 0xFF);
this->_bus->write(aAddress, 0xFF);
return 4;
}
}
if (this->controlRegister.direction == AToB) {
uint8_t data = this->_bus->read(this->aAddress.raw);
this->_bus->write(0x2100 | this->port, data);
uint8_t data = this->_bus->read(aAddress);
this->_bus->write(bAddress, data);
} else {
uint8_t data = this->_bus->read(0x2100 | this->port);
this->_bus->write(this->aAddress.raw, data);
uint8_t data = this->_bus->read(bAddress);
this->_bus->write(aAddress, data);
}
return 8;
}
@@ -90,14 +90,33 @@ namespace ComSquare::CPU
uint8_t DMA::run(unsigned int maxCycles)
{
unsigned cycles = 8;
int i = 0;
do {
cycles += this->_writeOneByte();
cycles += this->_writeOneByte(this->aAddress.raw, 0x2100 | this->port + this->getModeOffset(i));
if (!this->controlRegister.fixed)
this->aAddress.page += this->controlRegister.increment ? -1 : 1;
this->count.raw--;
i++;
} while (this->count.raw > 0 && cycles < maxCycles);
this->enabled = false;
return cycles;
}
int DMA::getModeOffset(int index)
{
switch (this->controlRegister.mode) {
case OneToOne:
return 0;
case TwoToTwo:
return index % 2;
case TwoToOne:
return 0;
case FourToTwo:
return (index & 0b11) > 1;
case FourToFour:
return (index & 0b11);
}
return 0;
}
}

4
sources/CPU/DMA/DMA.hpp
View File

@@ -36,7 +36,9 @@ namespace ComSquare::CPU
private:
//! @brief Write one byte using the A address, the port and the direction. Handle special cases where no write occurs.
//! @return The number of cycles used.
unsigned _writeOneByte();
unsigned _writeOneByte(uint24_t aAddress, uint24_t bAddress);
//! @brief Get an offset corresponding to the current DMAMode and the index of the currently transferred byte.
int getModeOffset(int index);
public:
//! @brief DMA Control register (various information about the transfer)
union {