Yesterday ARM introduced its highest performing and most power efficient display processor technology, the ARM® Mali™-DP650, which targets next generation premium and mass market devices.
The Mali-DP650 delivers performance and power efficiency gains of up to 2X compared to its predecessor, the Mali-DP550, in order to address the shift in mobile panel resolution from Full HD (1920x1080 pixels) to 2.5K formats including WQXGA (2560x1600 pixels) for tablets and WQHD (2560x1440 pixels) for a mobile screen. The Mali-DP550 remains the processor of choice for HD (1280x720 pixels) and Full HD devices.
Mali-DP650 offers enhanced 4K (3840x2160 pixels) capabilities and the ability to send 4K to a larger screen through WIFI streaming (e.g.Miracast) or via a connector (such as HDMI or USB-C). It enables more display processor use cases at 4K further reducing the requirement to engage other hardware blocks such as the GPU, thereby saving power and prolonging battery life.
Like its predecessor, the Mali-DP550, the Mali-DP650 offers an array of advanced features such as 7-layer composition, rotation, high quality scaling and a variety of pre and post-processing functions for video and graphics.
Mali-DP650: Performing functions such as composition, rotation, advanced scaling, colour conversion and tone mapping in a single pass through external memory
Addressing the performance challenges as mobile panels move towards 4K
Previously, it was thought that Full HD video and graphics content offered sufficient detail for a mobile screen. However, there is no doubt that being able to display video, UI and gaming content at even higher resolutions makes the overall output sharper and clearer. This has already led to a visible market presence of mobile screens capable of delivering higher resolutions - WQHD, WQXGA and even 4K is now starting to appear. This, however, poses a trade-off as handling higher resolution display layers natively means a costlier SoC in terms of both size and power consumption. Yet demand for such SoCs is growing and so therefore is the demand for effective solutions to address this issue with minimum impact on area, bandwidth and power.
Mali-DP650 doubles the available AXI bus width to 128-bits and adds significant memory subsystem optimizationswhich results in doubling the pixel throughput at the specified AXI clock rate. This exceeds performance expectations by being able to composite, process and display a combination of up to three full-frame 4K graphics and 10-bit video layers without any external intervention. This means that heavy composition use cases such as 4K video playback or gaming with UI overlays can be offloaded from the GPU onto the Mali-DP650 display processor, delivering power savings and allowing the GPU to focus on tasks it’s optimized for.
Mali-DP650 in a typical Mass Market Mobile system
Mali-DP650 also provides an MMU pre-fetcher solution to hide the delays caused by page table walks and enhances the overall interoperability with ARM’s CoreLink MMU-500 thus improving its overall tolerance to system latency. This translates to being able to build a lower cost interface to the display processor whilst still being able to deliver the same superior quality required by Full HD and beyond state-of-the-art mobile panels.
ARM Frame Buffer Compression (AFBC) is a system bandwidth saving technology which is known to deliver up to 50% system bandwidth saving if implemented throughout the multimedia system (GPU, Video and Display). Mali-DP650 implements AFBC and further optimizes AFBC efficiency by ensuring superior performance with DDR controllers.
Mali-DP650 display output is compatible with MIPI (Mobile Industry Processor Interface) DPHY transmitters. The Mali-DP650 offers split-display mode which is necessary to be able to talk to MIPI DPHY mobile panels with screen resolutions beyond Full HD. Split display mode allows for an image to be split into two equal parts at the display output thereby allowing two separate MIPI DSI transmitters to be driven in parallel. This doubles the available data rate making display resolutions up to 4k a reality on mobile or tablet devices.
Variable refresh rate saves power on the mobile panel
A display processor sends out pixel information to be displayed at a refresh rate that matches the rate at which the panel refreshes. In most systems today this is 60 times a second (60Hz/60fps). If the display processor did not send the information at the required rate then the panel would not be able to synchronize with the system and the visual output would not be displayed (or would be displayed with clear visual artefacts). Always sending output frames from the system to the panel at a fixed, and high, refresh rate has a key disadvantage. Even when the system is producing new visual information at a much slower rate (e.g. during video playback or when displaying a static webpage), the display processor is still running at the high refresh rate in order to keep the panel fed with information. In mobile, battery-powered systems this is detrimental to the battery life as the majority of the display subsystem must remain running continuously. To counter that, Mali-DP650 supports variable refresh - a technique whereby the output signal from the display processor is not transmitted at a constant and fixed rate but can vary on a per frame basis. The lowest frame rate will depend on the panel itself but a typical target would be 30Hz, which contributes to a longer battery life.
Enabling more composition use cases at resolutions beyond Full HD
Mali-DP650 can receive the 10-bit per pixel 4K video layer in either AFBC or YUV formats alongside additional UI layers (RGB888a or AFBC formats) and composite them with alpha blending. It can also rotate, downscale or upscale to the required resolution and even tone map the final output before sending it to the display. All of this functionality is performed in a single pass through the display processor without having to write back to external memory, thereby significantly reducing the overall system bandwidth and consequently, the power consumption. In addition, Mali-DP650 can be configured to act as a content passport for users as they move from a smaller mobile screen to a larger screen - 4K streaming video playback to external 4K displays via either HDMI, USB-C or through Wi-Fi transmission.
Another common video use case on a mobile device is a mobile video call via IP. This requires simultaneous video streams, one from the local camera and one from the other device, to be composited as a picture-in-picture (PIP) on the mobile display. The Mali-DP650 display processor enables PIP on the mobile display by allowing composition for the two video layers along with an additional graphics UI overlay, and can also upscale or downscale to meet the requirements of the local mobile panel. This again provides system-wide power savings by enabling composition, rotation and scaling without having to engage the GPU.
And it’s not just about the hardware…
Mali-DP650 is delivered with an Android HW Composer driver and an associated ADF-based Kernel Driver optimized to work alongside Mali GPU and Mali Video drivers. The ADF kernel device drivers are licensed under GPLv2 and are available in the driver section of the Mali Developer Centre. For more information on the Mali Display Android drivers, please check out the following blog: Do Androids have nightmares of botched system integrations?
In summary…
The Mali-DP650 display processor is 4k capable and optimised for 2.5k. It offers new features and performance enhancements that enable beyond Full HD mobile and tablet displays with optimal power usage. Mali-DP650 aims to drive new visual content and gaming experiences on mobile devices and act as a content passport for users as they move from a smaller mobile screen to a larger screen, such as a 4K smart television. Mali-DP650 further expands the Mali family of display processors, including Mali-DP550, which remains the processor of choice for mobile panels below Full HD. Display processors are critical for enabling the best overall user experience and prolonging the battery life of the device and we expect the Mali-DP650 to begin appearing in devices from early 2017.