General utilities and information relevant to ece4760 at Cornell.
All examples and student code are written using the Protohreads framework for multithreading.
- Protothreads 1.3 (written by Adam Dunkels) to be used 2025
The port to the rp2040 also works with rp2350. The basic protothreads scheme is extended for two cores with support for hardware locks, core-safe semaphores, and core-to-core hardware FIFOs. Protothreads provides a simple, cooperative, thread environment with very fast context switch and low memory overhead. Modified thread dispatcher implements priority scheduling in addition the default round-robin. The code linked below is the full demo with, locks, semaphores, FIFO and both cores running,
rp2350 codeand demo ZIP.
- Visual Studio configuration.
Configure VS for editing, programming, debugging using the Pi Debug Probe.
Refer to VScode extension and the getting started guide.- Add program/reset button
A trivial hardware and software addition simplifies programming.
Superceded by using the debugger.
- Add program/reset button
The rp2350 has twice the memory, so there is space for more VGA graphics modes.
There are three changes necessary to port the VGA driver to rp2350. The VGA Hsync and Vsync
PIO programs must have the clock dividers changed from 5 to 6 to account for the faster
system clock (150 on rp2350 vs 125 on rp2040). The RGB PIO program pixel delays need
to extended one cycle/pixel, again for the system clock change. The 4-bit color has two bits of green.
Two bits of green allows more shades of blue and red, and adds orange. Color Map
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- VGA 16-color 640x480 with better fonts
rp2350 Demo code, project ZIP.
- VGA 16 640x480 3D perspective polygon render.
The rp2350 version can render many more polygons than the 2040.
To demo this, a larger parametric surface is rendered with 400 triangles.
3D polygons are rendered in perspective by full 4D matrix transfroms.
rp2350 Demo code, project ZIP.
The rp2350 has hardware floating point instructions, as well as an improved integer multiplier and divider.
The integer multiplier now produces a full 64 bit result from a 32x32 multiply. This speeds up the fixed point multiply by about a factor of 5.
The pare includes ome test programs attempt to estimate the speed of the operations.
Video below compares float to fix for Mandelbrot set.
- Overlapped FFT with overlapped iFFT to reconstruct input signal
This a loop-back example to show that it is possible to do framed signal
processing without too much frame discontinuity between frames.
- String instrument synthesis by Karplus-Strong Algorithm
A cheap way to solve the linear wave equation on a string fast enough for
real-time sound synthesis - String synthesis by brute-force wave equation solution.
Finite difference solution of wave equation.
- Gravitational system in floating point.
Gravity is a long-range force, so the force computations are O(n2) in the
simplest implementation get big quickly. The example animates 150 gravitating particles
at about 140 frames/sec or 300 at 30 frames/sec.
Graphics input and output using 640x480 VGA, with optional joystick or encoder wheel.
Mouse interface is also shown in the USB section.
The serial interface is not really graphics, but plays around with color and formatting.
- VGA 256 color 319x240. (LWIP compatable, protothreads 1.3, PIO bug fix)
An extension of Hunter's PIO VGA driver for 8 bit color.
Three bits of green, three bits of red, and two bits of blue. - Serial command interface
Modern serial terminal emulators can produce a good looking user interface. - Joystick and encoder wheel with VGA
A simple analog joystick with select button, and a digital encoder wheel with direction and selector buttons. - Mouse controlled graphics.
See USB HID examples below.
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Everyone needs more memory. FRAM works well for simple files with bandwidth requirments below about 1.5 Mbyte/sec.
SD card with FatFS has a larger program size overhead, but is compatable with PC read/write of huge files.
USB FLASH drives are exzplained the the USB MSC example below.
- FRAM memory for PICO.
Nonvolitile FRAM to add 0.5 MB of serial RAM. - SD card with FatFS
MicroSD card support with PC-compatable file system - USB mass store MSC (see USB section below)
LWIP is the supported TCP/IP stack for the PicoW.
LWIP has lots of options and somewhat limited documentation.
This section has lots of examples to exercise some of the options.
Opotions include bringing up the PicoW as an WIFI access point or WIFI station and
data transfer by UDP or TCP.
- TCP protocol
- AP/HTML server on picoW to Browser as control/data display.
Using the rp2040 as an access point with web server allows a cellphone or
other web browser to act as a control panel for applications running on the rp2040.- (depricated) Browser as a control panel for rp2040. (version 2)
- (depricated) Standalone WIFI access point and web server (initial version)
This is an example from the C SDK repository that I used to understand more of LWIP.
- (depricated) Browser as a control panel for rp2040. (version 2)
- AP/HTTP server on picoW to client/viewer on picoW.
Use HTTP protocol to serve interactive, text, pages to another picoW.
The intent is a remote control panel and data display.
- AP/HTML server on picoW to Browser as control/data display.
- Network Time Protocol
- LWIP and VGA display of NTP and RTC
The LWIP and Hunter's VGA both use significant hardware. With care they are compatable and run at the same time. - Network Time Protocol (NTP) and the onboard real-time clock (RTC)
The NTP can be used to automatically set the rp2040 RTC, perhaps daily, to maintain accuracy. The Pico board clock oscillator is rated at ±30 ppm, or accuracy of 3x10-5. Since there are 86400 seconds/day, this means up to 2.6 sec/day drift.
- LWIP and VGA display of NTP and RTC
- UDP protocol
- Symmetric send/receive between two picoWs (access point to station)
Each picoW can send or receive packets.
The code running on the two nodes is almost identical. - Audio-rate UDP from picow to picow (access point to station)
Sending real-time data from picow to picow with no router involved. - Data array UDP send/receive (station to station thru hotspot)
Sending an array of data allows performance testing as well as understanding of data sizes, and dealing with packet efficiency. - UDP send/receive from desktop (station to station thru hotspot)
UDP protocol is a simple and fast, but does little error checking. It is therefore useful for data streams where a bad value is not a show stopper. You might send music but not code. - UDP send/receive pico-to-pico. (station to station thru hotspot)
A simple scheme for figuring out IP addresses on the fly allows two picos to send data to each other.
- Symmetric send/receive between two picoWs (access point to station)
USB uses the tinyUSB implementation and is fairly big.
There are lots of ways to use it. Examples are your friend.
- USB HID host with mouse and keyboard
Connecting a mouse and keyboard with video display of results. - USB host with HID and MSC
USB flash drive, Keyboard, mouse - USB device
More numerical flogging of the M0 architecture, with an emphisis on speed using 16-bit fixed point.
The IIR and FIR sections use design implementations which run completely in C on the the M0, at the
cost some slightly non-optimal designs.
- IIR filter designer
Using s1x14 fixed point format. Lowpass, bandpass, and highpass filters design. Plots the Bode plot of the designed filter, and allows the new filter to be used in realtime for audio input. - FIR filter designer
Using s1x14 fixed point format. Lowpass, bandpass, and highpass filters design. Plots the Bode plot of the designed filter, and allows the new filter to be used in realtime for audio input. Also a version for linear frequency plots. - Speech compression/playback from IIR filterbank.
Speech sampled at 12.8 Ksample/sec is sent through 32 MEL-distibuted IIR filters.
The filter powers are sampled every 20 mSec and used to reconstruct speech using DDS. - FFT and FilterBank spectrograms
FFT compared to lower resolution MEL spectrum for speech input. - FFT Spectrogram
Plotting the power spectrum, log power spectrum, and spectrogram of voice signals. The spectrogram actually has enough info to decode what is being said. - DSP development
IIR filters in fixed point s7x24 format. Butterworth lowpass and bandpass filter.