Memory Optimisation on AVR Microcontrollers for IoT Devices’ Minimalistic Displays

The minimalistic hardware of most Internet of things (IoT) devices and sensors, especially those based on microcontrollers (MCU), imposes severe limitations on the memory capacity and interfacing capabilities of the device. Nevertheless, many applications prescribe not only textual but also graphical display features as output interface. Due to the aforementioned limitations, the storage of graphical data is however highly problematic and existing solutions have even resorted to requiring external storage (e.g., a microSD card) for that purpose. In this paper, we present, evaluate and discuss two solutions that enable loading fullscreen, optimal 18-bit colour image data directly from the MCU, that is, without having to rely on additional hardware. Importantly, these solutions retain a very low footprint to suit the microcontroller architecture; the AVR architecture has been selected given its popularity. The obtained results show the feasibility and practicability of the proposal: in the worst case, 21 Kbytes of memory are required, in other words approximately 33% of the flash memory of a 32-Kbyte MCU remain available.