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HDMI
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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