This is how your laptop screen receives an image from the GPU

portable tablet screen

The arrival of OLED screens, as well as the DisplayPort 2.0 standard as an external video interface, has forced VESA to improve eDP to 1.5. But, what do these acronyms mean and how important are they in the future of GPUs and the screens that we use in our computers?

If you have ever wondered how it is possible for a laptop, a tablet, a smartphone or a portable console to receive the video signal without a video connector visible to the naked eye, then read on, you will learn how the Magic.

What does the acronym eDP stand for?

eDP is the acronym for embedded DisplayPort and refers to when this type of video interface and its signal are not obtained through an external interface to which a cable is connected, but internally. So it is the video interface used in systems with integrated screen. In other words, the eDP is the video interface that is used in laptops, pocket video game consoles, tablets and smartphones. So if you have a laptop and have ever wondered how the main hardware unit sends information to your PC screen, now you know how this type of connection is made.

Another of the functions of the eDP interface is to power the screen, not just transmit the video signal, since in devices that have it embedded they do not have an additional external power port.

Relationship with the GPU

eDP connector

Internally, the eDP does not differ at all from a DisplayPort interface. It is when the internal wiring reaches the perimeter of the device board that its signal is transformed into an external interface, which can be an eDP connection to connect the screen of a tablet or a laptop, a conventional DisplayPort output in any of its variants , a USB-C Alt-DP output, and even an HDMI output if there’s such a controller in between.

And here we enter into a little secret, at the level of generating the signal for several screens at the same time, the part of the GPU in charge of it has an eDP interface per supported screen, which is converted on the fly into another type of signal if the device needs it. In other words, your gaming graphics card also uses an eDP interface.

What is eDP 1.5?

eDP 1.5

Normally, the eDP and Display Port standards go hand in hand, but the body in charge of creating these standards, VESA, has decided to give the nth version of its embedded DisplayPort the name of eDP 1.5, instead of 2.0. This comes after 6 years, as its predecessor eDP 1.4b was released in 2015 and the new version of the standard is an incremental improvement over the previous one. Which means that it does not delete anything, but rather adds improvements to what has already been done previously.

The first novelty to highlight is the screen refresh author, to understand it we have to imagine that we have our computer or smartphone stopped doing nothing at all and it does not stop sending, therefore, the same image over and over again. This means that the GPU and video RAM will be active. Well, with the refresh author mode we can make the screen store the last image displayed in an internal memory and read its information from there while the GPU is off. This means great energy savings.

Another important point that we believe should be highlighted is the ability to disconnect the sending of data to the panel in the periods in which it is not necessary to send the information, known as VBlank. This is crucial for when we don’t have an image buffer on the system and the image is rendered line by line, old TV style.

eDP 1.5, designed to save on consumption

eDP 1.5

One of the improvements that VESA has added in eDP 1.5 is the so-called Replay Panel, which allows us to update only specific parts of the screen while leaving the rest totally intact, for this it also takes advantage of the ability to store in memory the last image displayed.

In general, the eDP 1.5 interface is designed to increase or reduce its consumption depending on the level of workload to be carried out. Thus, not only in lower resolutions and refresh rates will it consume much less than in higher ones, but it will also not emit anything during the periods in which the signal is not sent to the screen. Especially highlighting the inactivity between frames.

Although the screen does not show anything, the fact that the signal is active is a significant energy consumption. Temporarily turning off frame delivery also means turning off the system’s graphics hardware for that short period of time or reducing its clock speed.

A-SYNC for movies in eDP 1.5

Adaptive Sync means that the refresh rate and, therefore, the screen refresh rate is not controlled by the screen’s internal processor, but by the graphics hardware itself to which the screen is connected. Which in the case of your computer would be the graphics card. This ability was already in the previous version, but has been slightly improved in the new version.

It is a function related to video games where these tend to fluctuate unless we play with variable resolution, in which the FPS rate is maintained by sacrificing the number of pixels on the screen for it. Well, in eDP 1.5 this has been added for video playback in order to eliminate frame duplication, known as stuttering, and frame skipping.

For gaming panels, VESA has added new mechanisms to the new standard to reduce flickering on high-frequency screens.

Related to DisplayPort 2.0

DisplayPort-2.0

All the novelties that we have described require to be supported at the hardware level. Which translates to making changes to the display driver found in the GPU, it is a video communication protocol that as of the end of 2021 we have not yet seen a single product announced that supports eDP 1.5.

And the necessary changes not only have to be made in the hardware that generates the frame and receives it, but also in the one that receives it to show the image that the screens themselves are. This reminds us that much of the functions of the DisplayPort 2.0 are in the eDP 1.5. So, for example, a laptop with an internal eDP 1.5 interface will most likely have a DisplayPort 2.0.