maglev-ti-rtos

Example of PID controller usage applied to magnetic levitation.

Overview

Magnetic levitator on the base of Texas Instruments TIVA-C TM4C123GH6PM ARM Cortex-M4F MCU (EK-TM4C123GXL board). Regulation is performed by PID algorithm. Remote monitoring and control is provided by external Ethernet controller chip Microchip ENC28J60 (UDP commands).

Theory

In terms of control systems' general theory there're 4 main components: object under control; actuators and drivers; controller itself; feedback loop. Applied to this magnetic levitation system, these components are:

• Object: permanent magnet
• Driver: electromagnet, schematic plus PWM (see maglev-hardware)
• Controller: PID algorithm executed by the MCU
• Feedback: Hall sensor We specify setpoint (desired voltage depended on mutual arrangement of permanent and electro magnets) and get status of the process variable by Hall sensor (feedback value).

Software

MCU firmware (server)

This version of maglev use TI-RTOS (v.2.16.01.14 at the moment) real-time operating system to manages all tasks:

• initTask task. Performs initial setup of clocking system, GPIO, EEPROM, PWM, PID, ADC, SPI, UART, etc;
• consoleTask task. Used for setting IP/Port pair through the UART interface;
• ADCTimer timer. TI-RTOS' Timer instance firing every 1 ms and triggering ADC to start measurements;
• ADCHwi hwi. TI-RTOS' hwi (hardware interrupt) instance managing getting ADC results and also calling PID mechanism;
• UDPserverTask task. Vital task that constantly looking for UDP commands;

Generally, have been used the approach of dynamic creation/deletion of threads to reduce memory usage. For example, initTask is created before RTOS starts and then removed after doing its jobs. For remote control have been used ported from AVR lightweight driver and network stack for ENC28J60.

PC/Mac client

For remote control client see maglev-client (Python-based).

Installation

Due to not always proper work of TI CCS (Code Composer Studio) (exporting/importing projects) this repository is just set of necessary files. It's recommended to create brand new clean TI-RTOS project and simply put all these files (except .cfg one) into it. You better manually set tasks and SYS/BIOS parameters. There are 2 available build configurations: Debug and Release. Besides obvious compiler optimizations and all other jobs, Release and Debug configurations also differentiates in main code and .cfg script. Debug one uses semihosting mechanism because it's more handy to print all debug information in the same window while Release version route all strings to the UART (USB virtual COM port in case of EK board). Also, function of setting IP/Port in EEPROM is enabled only in Release because otherwise you can just edit code to change them. To switch between configurations use RELEASE_VERSION directive and see also "System configuration" part of maglev.cfg file.

Known issues

Besides probably not ideal SW architecture :), there is a strange behavior of PWM module. All current values of registers indicate that levitation shouldn't actually work, but it does. See forward to understand this fact.

Hardware

For schematic and PCB see maglev-hardware (KiCad EDA).

Copyright

All third-party software components (ip_arp_udp_tcp stack, enc28j60 driver and so on) belongs to their authors.