Timing Feasibility of Multimodal Software-Defined Haptic Rendering with a Browser-Based Digital Twin on a Cortex-M4 Microcontroller

Haptic interfaces convey force between an operator and a physical or virtual environment, yet passive devices encode a single force behavior in dedicated mechanical hardware and cannot emulate qualitatively different phenomena without physical modification. This study presents a software-defined haptic platform that renders four models on a single low-cost 32-bit microcontroller without hardware reconfiguration. A deterministic 1 kHz interrupt-driven control loop drives a motorized linear slider through an H-bridge and renders virtual detents, square-root position-dependent resistance, a one-dimensional reaction–diffusion field solved by explicit finite differences, and a symmetric square-root spring. A browser-based three-dimensional visualization, synchronized with the embedded state over a one-way serial link, forms a shadow Digital Twin, and a two-level limit-switch layer provides end-of-travel protection. The loop period, the worst-case execution time of the field solver, and the telemetry interval were measured on the deployed firmware. The control loop held its 1 ms period with microsecond-level jitter while streaming telemetry to the Digital Twin at approximately 5 Hz, and the field solver consumed less than 8% of the interrupt budget. These results show that reconfigurable multimodal haptic rendering can be scheduled deterministically on resource-constrained embedded hardware, whereas the physical fidelity of the rendered behaviors remains to be validated.