Energia: Code on a Timer with Tiva / Stellaris Launchpads

Do you wish you could smoothly fade LEDs without having to code that into the main loop of your program?  Do you wish you could sample sensors or input ports an a regular basis while doing other activities in the main part of your Energia program?  Are you looking for simple ways of creating periodic activities without having to worry about timing loops or how long other processing takes in your loop() function?  If so, then you want to use a timer interrupts!

This post describes how to run time based code in a Tiva/Stellaris Launchpad with 1ms precision. The same code runs on the MSP430 Launchpad with 2ms precision. Your function will be invoked at the interval you register without having to integrate any code in your run loop. The timer is in github along with a simple blinking light demo program.

Usage



AnyMsTimer calls a function()  on regular intervals independent of work you are doing in the the loop() function or the functions it calls. Register your function with AnyMsTimer along with the millisecond interval desired between calls.  Start the timer when you're ready to start receiving messages.

Notes

  1. The 2015/02 implementation supports only one timer function.
  2. You should do as little as possible in your timer function.  Other processor activities like UART or communication may be paused during your handler.
  3. The MSP430 timer behavior is different since there is no SysTick feature.

Basic operation

Energia configures Systick  to invoke functions in SysTickHandler every 1 ms.  You setup AnyMsTimer, passing your function and the desired calling interval. SysTickHandle() calls AnyMsTimer every millisecond. It counts the number of millisconds until it reaches the configured threshold when it calls your function. This continues process repeats

More info on Underlying Architecture

SysTick functionality is part of the core ARM standard.  All CPUs Invoke a function whose address is stored in the ARM Interrupt vector table and the SysTick address. Energia defines the interrupt vector table in startup_gcc.c.  It puts the address of SysTickIntHandler() in the interrupt vector table. 

User programs register their call back functions with registerSysTickCb().  That function stores the registered function in the SysTickCbFuncs[] array. AnyTimerMs (2/2015) only supports one timer function even though registerSysTickCb() appears to support up to 8 functions.

SysTickIntHandler is implemented in wiring.c. SysTickIntHandler is invoked every tick cycle, one time per millisecond on the LM4F and other boards.  SysTickIntHandler() sequentially invokes void function(uint323_t)  functions stored in SysTickCbFuncs[].  



The vector entry cannot be moved on ARM CPUs.  SysTickIntHandler() cannot be changed without changing the Energia library code.

Related Energia code in GitHub


Last Modified

2/25/2015






Comments

Post a Comment

Popular posts from this blog

Installing the RNDIS driver on Windows 11 to use USB Raspberry Pi as network attached

Image
I do a lot of my development and configuration via ssh into my Raspberry Pi Zero over the RNDIS connection. Some models of the Raspberry PIs can be configured with  gadget drivers  that let the Raspberry pi emulate different devices when plugged into computers via USB. My favorite gadget  is the network profile that makes a Raspberry Pi look like an RNDIS-attached network device.  All types of network services travel over an RNDIS device without knowing it is a USB hardware connection. A Raspberry Pi shows up as a Remote NDIS (RNDIS) device when you plug the Pi into a PC or Mac via a USB cable. The gadget  in the Windows Device Manager picture shows this RNDIS Gadget connectivity between a Windows machine and a Raspberry Pi. The Problem Windows 11 and Windows 10 no longer auto-installs the RNDIS driver that makes magic happen. Windows recognizes that the Raspberry Pi is some type of generic USB COM device. Manually running W indows Update  or  Upd...
Read more

Understanding your WSL2 RAM and swap - Changing the default 50%-25%

Image
The Windows Subsystem for Linux operates as a virtual machine that can dynamically grow the amount of RAM to a maximum set at startup time.  Microsoft sets a default maximum RAM available to 50% of the physical memory and a swap-space that is 1/4 of the maximum WSL RAM.  You can scale those numbers up or down to allocate more or less RAM to the Linux instance. The first drawing shows the default WSL memory and swap space sizing. The images below show a developer machine that is running a dev environment in WSL2 and Docker Desktop.  Docker Desktop has two of its own WSL modules that need to be accounted for.  You can see that the memory would actually be oversubscribed, 3 x 50% if every VM used its maximum memory.  The actual amount of memory used is significantly smaller allowing every piece to fit. Click to Enlarge The second drawing shows the memory allocation on my 64GB laptop. WSL Linux defaul...
Read more

Almost PaaS Document Parsing with Tika and AWS Elastic Beanstalk

Image
The Apache Tika project provides a  library capable of parsing and extracting data and meta data from over 1000 file types.  Tika is available as a single jar file that can be included inside applications or as a deployable jar file that runs Tika as a standalone service. This blog describes deploying the Tika jar as an auto-scale service in Amazon AWS Elastic Beanstalk.  I selected Elastic Beanstalk because it supports jar based deployments without any real Infrastructure configuration. Elastic Beanstalk auto-scale should take care of scaling up and down for for the number of requests you get. Tika parses documents and extracts their text completely in memory. Tika was deployed for this blog using EC2 t2.micro instances available in the AWS free tier. t2.micro VMs are 1GB which means that you are restricted in document complexity and size. You would size your instances appropriately for your largest documents.   Preconditions An AWS account. AWS ac...
Read more