Displays a live frame counter that increments every VBlank (60 fps NTSC, 50 fps PAL). The simplest possible real-time display on the SNES: read a hardware counter, render it as text, repeat.

Screenshot

What You'll Learn

How the NMI handler increments frame_count every VBlank — the heartbeat of every SNES game
How to use the text module for real-time number display
How WaitForVBlank() synchronizes the main loop to exactly 60/50 fps
How to read input with padPressed() for single-press detection

Controls

Button	Action
A	Reset counter to 0

SNES Concepts

VBlank and frame_count

The SNES PPU triggers an NMI interrupt at the end of every visible frame (scanline 225). The NMI handler in crt0.asm increments frame_count — a 16-bit counter that wraps at 65535 (~18 minutes at 60 fps). This counter is the basis for all game timing: animation delays, physics steps, input polling, and audio updates all synchronize to it.

WaitForVBlank

WaitForVBlank() blocks the main loop until the next NMI fires. This guarantees the game runs at a fixed frame rate. Without it, the main loop would spin freely and produce inconsistent timing.

Modules Used

Module	Why it's here
console	consoleInit(), WaitForVBlank(), NMI handler with frame_count
sprite	OAM buffer (required by NMI handler)
dma	DMA transfers used internally by console init
background	BG layer configuration
text	textInit(), textPrintAt(), textFlush() for counter display
input	padPressed() for single-press reset button

Build & Run

cd $OPENSNES_HOME

make -C examples/basics/timer

Open timer.sfc in Mesen2 and watch the counter increment.