DDC(9)

DDC(9) | Kernel Developer's Manual | DDC(9)

# NAME

`ddc` —
VESA Display Data Channel V2

# SYNOPSIS

`#include <dev/i2c/ddcvar.h>`

int
`ddc_read_edid`(i2c_tag_t tag, uint8_t *dest, size_t len);

# DESCRIPTION

The `ddc_read_edid`() reads a VESA Extended Display Identification Data block (EDID) via VESA Display Data Channel (DDCv2). DDCv2 is a protocol for data exchange between display devices (such as monitors and flat panels) and host machines using an I2C bus.

The tag argument is a machine-dependent tag used to specify the I2C bus on which the DDCv2 device is located. The dest argument is a pointer to a buffer where the EDID data will be stored. The len argument is the amount of data to read into the buffer. (The buffer must be large enough.) Typically, this value will be 128, which is the size of a normal EDID data block.

Normally the EDID data block will be post-processed with the `edid_parse`() function.

# RETURN VALUES

The `ddc_read_edid`() function returns zero on success, and non-zero otherwise.

# ENVIRONMENT

The `ddc_read_edid`() function is part of the ddc(4) driver, and is only included in the kernel if that driver is also included.

# EXAMPLES

The following code uses `ddc_read_edid`() to retrieve and print information about a monitor:

    	struct edid_info info;
    	i2c_tag_t        tag;
    	char		 buffer[128];

    	...
    	/* initialize i2c tag... */
    	...
    	if ((ddc_read_edid(tag, buffer, 128) == 0) &&
    	    (edid_parse(buffer, &info) == 0))
    		edid_print(info);
    	...

Note that this must be called before the PCI bus is attached during autoconfiguration.

# SEE ALSO

ddc(4), edid(9), iic(9)

# HISTORY

DDCv2 support was added in NetBSD 4.0.

# AUTHORS

Garrett D'Amore <gdamore@NetBSD.org>

May 11, 2006 | NetBSD 9.0