Developer Doug Brown has dug deep into precisely how a monitor makes its capabilities identified — so as, sarcastically sufficient, to not use a monitor in any respect.
“I lately discovered myself needing to alter the monitor that an inexpensive HDMI ‘dummy plug’ pretended to be,” Brown explains. “It was a random one I had purchased on Amazon a number of years in the past that acted as a 4k monitor, and I wanted it to be one thing less complicated that didn’t assist a 4k decision.”
So-called “dummy plugs” are tiny and quite simple digital units thatinsert into a tool’s video output and faux to be a monitor. Within the days of analog indicators, they could have been one thing as primary as a number of crossed wires and a resistor or two; in today of digital units, they’re just a little extra advanced — transmitting a knowledge bundle referred to as Prolonged Show Identification Information, or EDID.
Received a Raspberry Pi at hand? You then’ve all you could reprogram the EDID on a “dummy plug.” (📷: Doug Brown)
These units are ceaselessly used for “headless” operation, the place a gadget must assume there’s a monitor hooked up to be able to work correctly however can be accessed utilizing some type of distant desktop session. In Brown’s case, the HDMI dummy plug he had labored high quality — apart from the truth that it reported too excessive a decision, inflicting the digital desktop to exceed his desired decision. The answer: reprogramming the machine to report decrease capabilities.
“Conveniently,” Brown explains, “I discovered that my Raspberry Pi Zero has an I2C controller wired to the right pins on its HDMI port.” Utilizing this, Brown was capable of dump the present EDID from the dummy plug then dump one other from a seize card with the capabilities he was trying to emulate. “Lastly, I unplugged the seize machine and linked the dummy plug once more,” Brown continues, “and wrote the seize machine’s EDID to it.”
The unique EDID was backed up and verified earlier than a substitute was flashed onto the dummy plug. (📷: Doug Brown)
The consequence: a dummy plug that not reviews itself as a 4k-capable monitor, however as a substitute as a clone of Brown’s HDMI seize card. “I wish to make it clear that it might be doable to screw up a monitor should you observe these directions whereas an actual monitor is plugged in and it does not have its EDID protected,” Brown notes. “Additionally, be sure to are assured you’re on the right I2C bus! All the time learn the EDID and parse it first to verify it truly accommodates an EDID earlier than you try a write.”
The method is documented in full on Brown’s web site, full with a brief shell script for finishing up the reprogramming itself.
