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package nes
import (
"crecher.net/gones/v2/cart"
"crecher.net/gones/v2/cpu"
"crecher.net/gones/v2/ppu"
)
type Console struct {
CPU *cpu.CPU
PPU *ppu.PPU
Cart *cart.Cartridge
RAM [0x800]uint8
// APU, controllers once they exist
cycles uint64
}
func New(c *cart.Cartridge) *Console {
n := &Console{Cart: c}
n.PPU = ppu.New(c.Mapper, c.Mirroring)
n.CPU = cpu.NewCPU(n)
n.CPU.Reset()
return n
}
// Step runs one CPU instruction and the PPU dots (3 per CPU cycle) that
// elapse alongside it, firing NMI on a PPUCTRL/vblank edge. PPU state seen
// by bus accesses mid-instruction still lags behind by up to one
// instruction's worth of dots, since the CPU isn't cycle-stepped yet (see
// README: "CPU stall hook and proper IRQ/NMI line (polled between
// instructions)") - timing-sensitive register logic (the $2002 race window,
// NMI edge detection) is implemented to the real dot granularity and is
// exercised directly in the ppu package's tests, but end-to-end precision
// against real games/test ROMs needs that CPU work to land too.
func (n *Console) Step() int {
cycles := n.CPU.Step()
n.cycles += uint64(cycles)
for i := 0; i < cycles*3; i++ {
n.PPU.Tick()
if n.PPU.PollNMI() {
n.CPU.NMI()
}
}
return cycles
}
func (n *Console) StepFrame() {
// 29780 is roughly one frame:
// ~ 1789773 cycles per sec
// ~ 60.1 fps
// 1789773 / 60.1 = 29779.916...
const cyclesPerFrame = 29780
for done := 0; done < cyclesPerFrame; {
done += n.Step()
}
}
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