6.1.26. Variable Refresh Rate(VRR) and Auto Low Latency Mode (ALLM)
HDMI sink core is able to receive the video with variable refresh rate (VRR) transport. Since VRR involves runtime varying video vertical blanking, HDMI sink locked and vid_lock remains asserted when receiving video with VRR transport.
ALLM is enabled through the HF-VSI which can only be supported in sink auxiliary data port. You can capture the ALLM_Mode through the packet byte 5 bit 1 of HF-VSI through the sink auxiliary data port. Refer to HDMI 2.1 specification section 10.2 HDMI Forum Vendor Specific InfoFrame for more information.