From 780b1e886f6676efedc732b67328f5fbdbe87dc4 Mon Sep 17 00:00:00 2001
From: crecher <crecher@crecher.net>
Date: Mon, 12 Oct 2026 15:44:15 +0200
Subject: waiter waiter more comments please

---
 nes/bus.go | 21 +++++++++++++++++++--
 nes/nes.go |  6 +++++-
 2 files changed, 24 insertions(+), 3 deletions(-)

(limited to 'nes')

diff --git a/nes/bus.go b/nes/bus.go
index d9fd521..07bbbf2 100644
--- a/nes/bus.go
+++ b/nes/bus.go
@@ -1,10 +1,27 @@
 package nes
 
+// CPU memory map is:
+// Address range	| Size	| Device
+// --------------------------------------------------
+// $0000-$07FF		| $0800	| 2 KB internal RAM
+// $0800-$0FFF		| $0800	| Mirror of $0000-$07FF
+// $1000-$17FF		| $0800	| Mirror of $0000-$07FF
+// $1800-1FFF		| $0800 | Mirror of $0000-$07FF
+// $2000-2007		| $0008 | PPU registers
+// $2008-$3FFF		| $1FF8	| Mirrors of $2000-$2007 (repeats every 8 bytes)
+// $4000-4017		| $0018	| APU and I/O registers
+// $4018-$401F		| $0008 | APU and I/O functionality thats normally disabled (CPU test mode)
+// $4020-$FFFF		| $BFE0	| Unmapped, available for cartridge
+// - $6000-$7FFF	| $2000	| Usually cartridge RAM (if present)
+// - $8000-$FFFF	| $8000 | Usually cartridge ROM (if present)
+
+// wow i put way too much effort into making that table
+
 func (n *Console) Read(addr uint16) uint8 {
 	switch {
-	case addr < 0x2000:
+	case addr < 0x2000: // internal RAM and mirrors
 		return n.RAM[addr&0x7FF]
-	case addr >= 0x4020:
+	case addr >= 0x4020: // cartridge
 		return n.Cart.Mapper.CPURead(addr)
 	default:
 		return 0
diff --git a/nes/nes.go b/nes/nes.go
index 0f2a754..7f36b1a 100644
--- a/nes/nes.go
+++ b/nes/nes.go
@@ -27,7 +27,11 @@ func (n *Console) Step() int {
 }
 
 func (n *Console) StepFrame() {
-	const cyclesPerFrame = 29780 // 29780 ~ 1789773 / 60.1
+	// 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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