Edid Definitions; Additional Segments; Figure 134: Reading Sink Edid Through Adv7850 - Analog Devices ADV7850 Hardware Manual

EDID Definitions

13.13.2
Extended EDID (E-EDID) supports up to 256 segments. A segment is a 256-byte segment of EDID data containing one or two 128-byte
EDID blocks. A typical HDMI sink will have only two EDID blocks and so will only use segment 0. The first EDID block is always a base
EDID structure defined in the VESA EDID specifications; the second EDID block is usually the CEA extension defined in the CEA-861
specification.
The ADV7850 has a single memory location used to store EDID and HDCP information read from the downstream sink. During HDCP
repeater initialization, the EDID data read from the sink is overwritten with HDCP information which is also read from the sink. The sink
EDID is not reread after HDCP initialization. The user can request the ADV7850 to rebuffer an EDID segment by using edid_read_en.

Additional Segments

13.13.3
The EDID block 0 byte number 0x7E tells how many additional EDID blocks are available. If byte 0x7E is greater than 1, additional EDID
segments need to be read. If there is more than one segment, the second block (that is, block 1) is required to be an EDID extension map.
This map should be parsed according to the VESA EDID specification to determine where additional EDID blocks are stored in the sink
EDID storage device (that is, EEPROM, RAM, and so on).
The ADV7850 is capable of accessing up to 256 segments from EDID of the sink as allowed by the EDID specification. By writing the
desired segment number to edid_segment[7:0], the ADV7850 will automatically access the correct portion of the sink EDID over the Tx
DDC lines and load the 256 bytes into the EDID/HDCP memory. When the action is complete, the ADV7850 triggers the edid_ready_int
interrupt. The EDID data read from the sink can then be accessed from the Tx EDID Map. If the host controller needs access to
previously requested EDID information, then it can be stored in its own memory.
Figure 134 shows how to implement software to read EDID from the downstream sink using the ADV7850.
Power up Tx via
SYSTEM_PD
Wait for EDID
Ready Interrupt
EDID_READY_INT
Read EDID data
from TX EDID
Map
Rev. A May 2012
START
Wait for HPD
interrupt HDP_INT
Set
EDID_SEGMENT
desired Segment
Need
Parse EDID
Additional
Data
Blocks?

Figure 134: Reading Sink EDID Through ADV7850

Disable EDID
Interrupt
NO
EDID_READY_INT
until next HPD
381
ADV7850
Setup Audio and
Video