If a static is being displayed by HDMI2USB (for example a slide in a presentation), then it is difficult to tell whether the HDMI2USB is working or it is hung. So a heart beat feature has been added which causes a block of pixel to pulse in the lower right corner of the screen indicating that HDMI2USB is alive.
How to control?
Heart Beat (HB) can be switched on/off using switch SW 0 or using the CDC control port by sending ASCII command "S(s)" and "H(h)". But the control port will work only when the switch is on. So the switch acts as a "hard off" signal.
How to tweak the pulse?
The heart beat module is instantiated in the image_selector module. To change height, width and pulsing rate of the pixels, change the generics HB_length, HB_width and alt_aft_frame in hdl/misc/image_selector.vhd file.