projects

Hardware/software projects
2022 - 2024
rp2040 micropython and MBED

rp2040 Microcontroller older material
- MicroPython -- I played with this system for a couple of months just after the PICO was announced. Python is a very nice environment, but fairly slow for real-time programming. I got DMA running, but it was tedious because Python really does not want you to mess directly with memory. In the end, we decided to move to straight C-SDK for development.
  Applications:
  - A simple program to sample the ADC and copy the values to a PWM channel at 500 Ksamples/sec using zero cpu cycles.
  - I figured out a DDS system using the settable DMA transfer clock to produce sinewaves on a pwm channel with no cpu cycles.
- MBED/Arduino -- The MBED framework (arduino site) allows use of a simple RTOS on core0, while running bare C-SDK on core1. The tool chain is installed in the usual trivial Arduino way. Speed is good and the RTOS is quite handy. It is a bit confusing because there are three different peripherial libraries to handle: Arduino, MBED, and C-SDK. I completely eliminated the Arduino constructs and used a mixture of MBED and C-SDK. Using the PIO subsystems required an external assembler for the PIO assembly language and was a little inconvenient. In the end, we decided to move to straight C-SDK for development.
  Applications:
  - ADC and PWM DAC using DMA with
    ADC>DMA>PWM on Core0
    DDS>DMA>PWM on Core1
    The DDS algorithm is completely carried out by a DMA channel and the PWM DAC.
  - A PIO input event time/duration capture which works up to about 10 MHz.The RP2040 has no "input capture" peripherial that uses hardare to grab a time stamp for an external event (edge on i/o pin). Both the AVR and PIC32 that I have used can capture times in hardware, and I find it useful. The PIO can be used to implement a fast timer/counter, detect i/o pin edges, and log the time stamps at full bus rate to a 8-slot hardware FIFO.
  - PIO based stepper motor drivers that took high level move commands from the cpu. The implementation ran two motors. You specify steps/sec, pattern, and step count for each motor. The pattern can be forward/backward using steps/half-steps. The motors run until the step count is reached, then the PIO throws an interrupt.
  - DMA and PIO based NTSC video generator which used zero cpu cycles to refresh the screen.
    there are 255x200 1-bit black/white and 4-bit gray scale versions. One use of this was to simulate diffusion-limited aggregation.
  - A scheme to extract the dominant frequencies (called formants) of vowels in speech. This is mathematically involved (three FFTs), but runs in real-time on the two cores. The code uses two interesting approximations. The first is the alpha-max, beta-min algorithm to speed up squareroot of sum-of-squares. It is accurate to within 2%. The second is an approximation of log base two from Generation of Products and Quotients Using Approximate Binary Logarithms for Digital Filtering Applications, IEEE Transactions on Computers 1970 vol.19 Issue No.02. It is accurate to within 0.02 log units.
  - There are also some tests for ISR speed, IIR fliter speed, and FIR speed. The FIRs are just fast enough to do Head Related Transfer Functions in real-time.
- Future:
  - packet radio or packet IR
  - adaptive filters
  - head related transfer function
- Obsolete ece4760 page -- for reference only!