Driving TFEL with RP2040: Offloading the CPU step by step (2021)
14 days ago
- #STN-LCD
- #PIO
- #RP2040
- The author discusses challenges in driving a monochrome 10.4" 640x480 TFEL panel with an STN LCD interface, which requires continuous refreshing at 120 Hz.
- Options for driving the display include using obsolete dedicated graphics controllers, ARM SoCs with LCD controllers, or display controller chips converting VGA to STN LCD signals.
- Alternative methods involve using a fast microcontroller with large SRAM to bit-bang GPIO or a CPLD/FPGA for timing generation.
- The author chooses to use the RP2040 microcontroller, leveraging its PIO (Programmable I/O) engine to offload CPU tasks and improve performance.
- Initial attempts with fully bit-banged GPIO resulted in noticeable flickering and high CPU usage, prompting the use of PIO for data transmission.
- Further optimization involved using DMA (Direct Memory Access) to handle data transfer, significantly reducing CPU load.
- The final solution integrates PIO for both data transmission and sync signal generation, achieving minimal CPU usage (0.009%) and efficient display driving.
- The author provides full source code under the MIT license, encouraging others to adapt and optimize the solution for their projects.