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27 Jul 2017, 8:22

Design your own HMI using the RX71M Revelation Kit GAPI Journey Document for free


Have you been challenged by your marketing team to design out the old LCD segment display in your application and refresh the design with latest TFT technology?

HMI (Human Machine Interface) requirement specifications are in a changing phase. Smart Phones have created customer expectation for “Smart HMIs” on all kind of devices and those days where a Segment LCD was accepted by customers are starting to vanish. Existing HMI solutions based on Segment LCD display are requested by marketing to be replaced by TFT based ones.

Sounds like a straightforward task for an engineer, if there wouldn’t be all the new challenges suddenly appearing on the way down this path, especially if it is your first TFT HMI design.

Several question may come to mind immediately:

  • Is the current MCU suitable to control the TFT?
  • Where to get the images to be displayed?
  • How to get the image data into my project resources?
  • Where to find a suitable software, without large budget investment?
  • How to keep to the design schedule and learn all these new things?

Luckily there is an answer to all of these and more. The nice GAPI Journey document, designed by Renesas, provides a helping hand to you. 

Get your project ready for start

The Renesas Graphics Application Programming Interface (GAPI) is a useful and flexible tool for creating a Human Machine Interface (HMI) on a Renesas RX-based system incorporating a touchscreen display.

Using the RX71M Revelation Kit as a hardware platform, the journey document shows how an application can be built up from the e2 studio project generator, describing the importation of Renesas Firmware Integration Technology (FIT) modules and the addition of source code components for FreeRTOS, Direct-Drive LCD (DDLCD) and GAPI. The purpose of each component and how they interact is explained in the document.

The new project creation is done in a step-by-step detail level, so that it would be easy to follow and to do your own steps accordingly.

It is started by creating an empty project using Renesas e2 studio project generator, including the tool chain selection suitable for the Revelation Kit. At the coding assistant tool selection the FIT module integration has to be selected. The Renesas Firmware Integration Technology (FIT) code modules provides a consistent API for the overlying software to access the peripherals of the RX71M (or other RX devices). FIT API offers a consistent interface to the peripheral function module drivers and therefore improves the portability between RX microcontrollers.

  • Aim of lightening the burden of program development.
  • Reduce the needs of software resource management.
  • Easy development using the RX Family.
  • Easy transition within the RX family without touching the application code.


Beside the FIT a few other components need to be added to the project to make it suitable for the base of your development. Again don’t be scared about this as it is all nicely descripted in the Journey document.

  • FreeRTOS

A real time operation system provides scheduling, timing and messaging functionality for the various tasks to communicate with each other and run together in a consistent, organised manner. In this case the FreeRTOS had been selected by Renesas to allow customers easy adaption.

  • Direct Drive LCD

The DDLCD package is responsible for updating the LCD display. It controls the driving of the display, using various timers with external pins and the external bus. It also manages the buffer memory area in RAM where the display “frames” are stored, and implements the timing of updates, so that changes are not being made to a frame while it is being output to the display, in order to minimise flicker.

  • Graphics Application Programming Interface

GAPI provide functionality for the creation and manipulation of graphic objects on the
display (actually on the frame in memory).

The source for the FreeRTOS, DDLCD and GAPI components can be copied directly from the RPBRX71M_GAPI project.

Build your own HMI demo

If you have followed the journey document you should have a blank GAPI project ready by importing the various elements: FIT modules, FreeRTOS, DDLCD, GAPI, existing code including touchscreen driver, resource builder and configuring the project on the RPBRX71M Revelation Kit hardware platform.

This new project can now be built, debugged and used as a base to develop GUI applications. The GUI application demo, descripted by the journey document, will consist of a home screen, and 2 child screens that will be entered by pressing an icon on the home screen.


Graphics in the demonstration are mainly in bitmap format, although jpeg images are supported by the included jpeg library (as part of the GAPI). In order for the application to be able to access the graphics, they need to be packaged together and embedded in the Flash for retrieval as required. All steps are shown to build the above HMI from scratch in a quite detailed level by the GAPI journey document.


It is proven by the journey document, that a proper documentation, detailing the difficulties to get started with a TFT HMI application, makes your own HMI design an easier task. The provided demo project can be adapted and modified to your custom needs, as all pieces of software are provided as source for your quick reference.

Moreover the 32-bit MCU RX71M as a system MCU on the Revelation Kit shows that the large embedded 552kB RAM and the 4MB Flash is suitable to drive a single chip HMI design without the need of addition external memory. In fact, the embedded 552kB SRAM of the RX71M MCU will be used for that purpose, leaving enough performance as well as memory for the application design, too.

Have a nice and successful engineering day!


Further details as well as the board schematic, demo projects, manuals etc can be found at:


The Journey document and the project file can be downloaded at:

A “Get started” book you can find (English PDF) download here:

For a German version of the book please follow this link:

Details about the Firmware Integration Technology (FIT) can be found here:

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27 Jul 2017, 8:22


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