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DDC(9) NetBSD Kernel Developer's Manual DDC(9)
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ddc -- VESA Display Data Channel V2
ddc_read_edid(i2c_tag_t tag, uint8_t *dest, size_t len);
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 pan-
els) 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 nor-
mal EDID data block.
Normally the EDID data block will be post-processed with the edid_parse()
The ddc_read_edid() function returns zero on success, and non-zero other-
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.
The following code uses ddc_read_edid() to retrieve and print information
about a monitor:
struct edid_info info;
/* initialize i2c tag... */
if ((ddc_read_edid(tag, buffer, 128) == 0) &&
(edid_parse(buffer, &info) == 0))
Note that this must be called before the PCI bus is attached during auto-
ddc(4), edid(9), iic(9)
DDCv2 support was added in NetBSD 4.0.
Garrett D'Amore <gdamore@NetBSD.org>
NetBSD 9.99 May 11, 2006 NetBSD 9.99