just do it

main.go

@@ -54,6 +54,7 @@ var (
 	show_refresh             = flag.Bool("led-show-refresh", false, "Show refresh rate.")
 	inverse_colors           = flag.Bool("led-inverse", false, "Switch if your matrix has inverse colors on.")
 	disable_hardware_pulsing = flag.Bool("led-no-hardware-pulse", false, "Don't use hardware pin-pulse generation.")
+	led_slowdown_gpio        = flag.Int("led-slowdown-gpio", 1, "GPIO pin slowdown")
 )
 
 //listens on topic for messages
@@ -213,9 +214,11 @@ func main() {
 	config.ShowRefreshRate = *show_refresh
 	config.InverseColors = *inverse_colors
 	config.DisableHardwarePulsing = *disable_hardware_pulsing
+	var rt rgbmatrix.RunTimeConfig
+	rt.Gpio_slowdown = *led_slowdown_gpio
 	setupMQTT()
 
-	m, err := rgbmatrix.NewRGBLedMatrix(config)
+	m, err := rgbmatrix.NewRGBLedMatrix(config, rt)
 	fatal(err)
 	mqMessages := make(chan mqtt.Message)
 	log.Println("making listener")