HDMI High-Definition Multimedia

InterfaceMythri P K

September 2010

Introduction• HDMI is a compact audio/video interface

for transmitting digital data.

HDMI communication channels

• HDMI has three physically separate communication channels, which are the DDC, TMDS, and the optional CEC – The HDMI cable and connectors carry four

differential pairs that make up the TMDS data and clock channels.

» Audio, video and auxiliary data is transmitted across the three TMDS data channels.

» A TMDS clock, typically running at the video pixel rate, is transmitted on the TMDS clock channel

HDMI communication channels contd..

– HDMI carries a VESA DDC channel. The DDC is used for configuration and status exchange between a single transmitter and a single receiver.

» The DDC is used by the transmitter to read the receiver’s Enhanced Extended Display Identification Data (E-EDID) in order to discover the receiver’s configuration and capabilities.

– The optional CEC protocol provides high-level control functions between all of the various audiovisual products in a user’s environment.

HDMI connector

• There are 3 Types of HDMI connector, Type A , B and C. All three connectors carry all required HDMI signals, including a TMDS link.

• The Type B connector is slightly larger and carries a second TMDS link, which is necessary to support very high resolution displays using dual link.

• The Type C connector carries the same signals as the Type A but is more compact and intended for mobile applications.

• The HDMI connector provides a pin allowing the transmitter to supply +5.0 Volts to the cable and receiver.

• All HDMI transmitters shall assert the +5V Power signal whenever the transmitter is using the DDC or TMDS signals

HDMI Link

• The HDMI link operates in one of three modes:• Video Data Period - the active pixels of an active

video line are transmitted• Data Island period - audio and auxiliary data are

transmitted using a series of packets.– This auxiliary data includes InfoFrames and other

data describing the active audio or video stream or describing the transmitter.

• Control period- It is used when no video, audio, or auxiliary data needs to be transmitted. It is required between any two periods that are not control periods.

Video Data on HDMI

• Video data can have a pixel size of 24, 30, 36 or 48 bits. Color depths greater than 24 bits are defined to be “Deep Color” modes.

• Video at the default 24-bit color depth is carried at a TMDS clock rate equal to the pixel clock rate.• Video Pixels Video Data Coding is such that the 8 bits

converted to 10 bits by HDMI transmitter.• The video pixels can be encoded in either RGB, YCBCR

4:4:4 or YCBCR 4:2:2 formats.• Deep Color modes are optional though if an HDMI

transmitter or receiver supports any Deep Color mode*, it shall support 36-bit mode.

AVI Infoframe

• An InfoFrame packet carries one InfoFrame. The InfoFrame provided by HDMI is limited to 30 bytes plus a checksum byte.

• HDMI transmitter shall always transmit an AVI InfoFrame at least once per two video fields if the transmitter supports.

• The AVI InfoFrame shall be transmitted even while such a transmitter is transmitting RGB and non pixel-repeated video.

• For AVI infoframe format refer : Section 8.2 in HDMI 1.3 specification

EDIDExtended display identification data

• HDMI transmitter shall read the EDID and first CEA Extension to determine the capabilities supported by the receiver.

• HDMI transmitter shall check the E-EDID for the presence of an HDMI Vendor Specific Data Block within the first CEA Extension to determine whether it is an HDMI/DVI device.

• All the receiver supports 640 * 480P video format by default.

• For detailed information on EDID format refer to

http://en.wikipedia.org/wiki/Extended_display_identification_data

Hot-Plug detect

• An HDMI receiver shall assert high voltage level on its Hot Plug Detect pin when the E-EDID is available for reading.

• HDMI receiver shall indicate any change to the contents of the E-EDID by driving a low voltage level pulse on the Hot Plug Detect pin.

Code flow in OMAP4• hdmi_init-

– It is called during bootup during the DSS probe along with other blocks like dispc, dsi , dpi etc.

– This registers the HDMI driver to DSS and registers HDMI IRQ handler.

• hdmi_exit – – Called from omapdss_remove , it will free IRQ

handler.

• Call flow when echo 1 > sys/devices/platform/omapdss/display*/enabled Is called

• hdmi_enable_display – Does the GPIO configuration for DDC and hot-plug detect level

shifter (GPIO60 and 41).– Enabled dss clk -> hdmi_enable_clocks– Reads EDID by calling hdmi_read_edid to determine the timing

supported by TV. See http://omappedia.org/wiki/RFCs RFC for autodetect for more information/

– Computes PLL based on the timing that is selected after reading EDID.

– Configures the HDMI PLL and PHY blocks hdmi_pll_program and hdmi_phy_init

– Configures the video and auxillary infoframe inforamtion based on the EDID by calling hdmi_lib_enable.

– Configures the dispc(display controller) gamma table and HDMI switch.

• Call flow when echo 0 > sys/devices/platform/omapdss/display*/enabled

Is called

• hdmi_disable_display– Disabled the dss_clk requested by HDMI.

Hdmi_enable_clocks(0).– Sets the power state of the HDMI PLL block to

ALL_OFF HDMI_W1_SetWaitPllPwrState– Set the PHY block to off hdmi_phy_off– GPIO configurations are pulled down.

References

• TI OMAP4 TRM

http://focus.ti.com/general/docs/wtbu/wtbudocumentcenter.tsp?templateId=6123&navigationId=12667

• HDMI 1.3 specification http://www.hdmi.org/learningcenter/faq.aspx

• EDID information

http://en.wikipedia.org/wiki/Extended_display_identification_data http://www.hdmi.org/learningcenter/presentations.aspx (Implementing EDID that works)

• Connector http://pinouts.ru/Video/hdmi_pinout.shtml