by Arda Erdikmen

A cycle exact frame number counter to test emulator render performance

Requires Sinclair Zx Spectrum computer with at least 48kb memory (or equivalent emulator).

Compile and create a loadable tape file with pasmo: pasmo.exe -v --tapbas fpscounter2.asm fpscounterout2.tap

There are two different versions. The screenshot shows the second one. Below image is a 50fps gif image.

it shoud look like this. (if your computer/browser cannot play 50fps gif, it should flicker and you should see red/green borders and other visual artifacts etc.)

upper part of the border should switch colors according to zx spectrum series, black to white. lower part of border should switch between red and yellow, producing a shade of orange/yellow colour. If you see a red or green border, your emulator skips frames.

Following image shows the two frames blended. The border and lower part of image should look like this.

Topmost part of screen shows frame number, 1 to 50. Middle part of screen shows short horizontal lines, switching position. They should look like grayish long horizontal line. If you sense they are moving through a direction, your emulator might skip frames. Bottom part of screen shows alternating checker pattern. If you see any kind of flashing at that area, it's a frame skip.

Best way to test your emulator is with using a hi-framerate video recorder. Use your smartphone's slow-mo 240fps recorder. Record a couple of seconds of footage. Watch and observe your emulator performance.