/
loopyRegister.go
152 lines (130 loc) · 4.12 KB
/
loopyRegister.go
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package ppu
import (
"github.com/raulferras/nes-golang/src/nes/types"
)
/*
LoopyRegister Internal PPU Register
The 15 bit registers t and v are composed this way during rendering:
yyy NN YYYYY XXXXX
||| || ||||| +++++-- coarse X scroll
||| || +++++-------- coarse Y scroll
||| ++-------------- nametable select
+++----------------- fine Y scroll
*/
type LoopyRegister struct {
_coarseX byte // 5 bits
_coarseY byte // 5 bits
_nameTableX byte // 1 bit
_nameTableY byte // 1 bit
_fineY byte // 3 bits
latch byte
}
func (register *LoopyRegister) address() types.Address {
var address uint16 = 0
address |= uint16(register._coarseX & 0b11111)
address |= uint16(register._coarseY&0b11111) << 5
address |= uint16(register._nameTableX&1) << 10
address |= uint16(register._nameTableY&1) << 11
address |= uint16(register._fineY&0b111) << 12
return types.Address(address) & 0x3FFF
}
func (register *LoopyRegister) nameTableAddress() types.Address {
var address uint16 = 0
address |= uint16(register._coarseX & 0b11111)
address |= uint16(register._coarseY&0b11111) << 5
address |= uint16(register._nameTableX&1) << 10
address |= uint16(register._nameTableY&1) << 11
return types.Address(address) & 0x3FFF
}
func (register *LoopyRegister) Value() types.Address {
var address uint16 = 0
address |= uint16(register._coarseX & 0b11111)
address |= uint16(register._coarseY&0b11111) << 5
address |= uint16(register._nameTableX&1) << 10
address |= uint16(register._nameTableY&1) << 11
address |= uint16(register._fineY&0b111) << 12
return types.Address(address)
}
func (register *LoopyRegister) setValue(address types.Address) {
register._coarseX = byte(address & 0b11111)
register._coarseY = byte(address>>5) & 0b11111
register._nameTableX = byte(address>>10) & 1
register._nameTableY = byte(address>>11) & 1
register._fineY = byte(address>>12) & 0b111
}
func (register *LoopyRegister) setNameTableX(nameTableX byte) {
register._nameTableX = nameTableX & 1
}
func (register *LoopyRegister) setNameTableY(nameTableY byte) {
register._nameTableY = nameTableY & 1
}
func (register *LoopyRegister) setCoarseX(coarseX byte) {
register._coarseX = coarseX & 0b11111
}
func (register *LoopyRegister) setCoarseY(coarseY byte) {
register._coarseY = coarseY & 0b11111
}
func (register *LoopyRegister) push(value byte) {
/*
if register.latch == 0 {
register.address = types.Address(Value&0x3F)<<8 |
(register.address & 0x00FF)
} else {
register.address = register.address&0xFF00 | types.Address(Value)
}
*/
// fY fY fy NY NX YYYYY XXXXX
if register.latch == 0 {
// fy fy fy NY NX Y Y] [Y Y Y X X X X X]
// [15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0]
// v v v v v v v v
// 0x3F => 111111 <<8 => 11111100000000
// Bits 0 and 1 go into bits 3 and 4 of CoarseY
register._coarseY = (value & 0x03 << 3) | register._coarseY&0b111
// bit 2 goes into NameTableX
register._nameTableX = (value & 0x04) >> 2
// bit 3 goes into NameTableY
register._nameTableY = (value & 0x08) >> 3
// bit 5,6 and 7 goes into FineY. bit 7 is cleared
register._fineY = (value >> 4) & 0b011
//register.address =
// types.Address(Value&0x3F)<<8 | (register.address & 0x00FF)
register.latch = 1
} else {
// bits 0,1,2,3, and 4 goes into CoarseX
register._coarseX = value & 0b11111
// bits 5,6 and 7 go into CoarseY[0,1,2]
register._coarseY = register._coarseY&0b11111000 | (value&0b11100000)>>5
register.latch = 0
}
}
func (register *LoopyRegister) increment(incrementMode byte) {
address := register.Value()
if incrementMode == 0 {
address++
} else {
address += 32
}
register.setValue(address)
}
func (register *LoopyRegister) resetLatch() {
register.latch = 0
}
func (register *LoopyRegister) NameTableY() byte {
return register._nameTableY
}
func (register *LoopyRegister) NameTableX() byte {
return register._nameTableX
}
func (register *LoopyRegister) CoarseX() byte {
return register._coarseX
}
func (register *LoopyRegister) CoarseY() byte {
return register._coarseY
}
func (register *LoopyRegister) FineY() byte {
return register._fineY
}
func (register *LoopyRegister) resetFineY() {
register._fineY = 0
}