Linux write message to log file from .service

As part of trying to debug the .service that I set up for installing the RTC chip on my BeagleBone at boot time, I was interested in writing messages to the Linux system logs from the shell script that it called. This turns out to be fantastically easy; there seems to be a couple of different commands that can be used, I went with the 'logger' command, as described in this link:

http://www.cyberciti.biz/tips/howto-linux-unix-write-to-syslog.html

Tkinter check boxes

Tkinter doesn't have widgets that look like switches like Labview or anything, but apparently most OS's can be counted on to have check boxes so that's a thing in Tkinter. Either I'm finally getting used to this or it's' pretty easy to find useful examples on how to define checkboxs and how to grey them out:

Basic man page. In the examples the author seems to like the grid manager, but pack works just fine: http://www.python-course.eu/tkinter_checkboxes.php

A reminder to use an IntVar to return the status of the checkbox: http://stackoverflow.com/questions/16285056/get-the-input-from-a-checkbox-in-python-tkinter

A compact man page with nice lists of parameters and methods, including disable. http://www.tutorialspoint.com/python/tk_checkbutton.htm

A similar page for buttons showing how you can use the same settings to grey them out too: http://www.tutorialspoint.com/python/tk_button.htm

Notes from compiling a kernel module from scratch

Found the debian SD image for BeagleBone that I started testing with so long ago. It's probably obsolete by now, but at least I know that it works.

Its name is bone-debian-7.8-lxde-4gb-armhf-2015-03-01-4gb.img

Used Win32DiskImager to write it to a blank 4G SD card from AdaFruit.

Beaglebone booted to LXDE desktop after a worrying 45 second pause (It might have been setting up the ethernet connection)

perform apt-get update

sudo apt-get update

Update Tkinter just because

sudoe apt-get install python-tk

start python, verify tkinter installed to make sure that the last installs worked.

$ which python
$ python
import os
import Tkinter
^d

get my kernel version:

$ uname -r
3.8.13-bone70

attempt to get the source tree headers:

$ sudo apt-get install kernel-headers-$(uname -r)
E: Unable to locate package kernel-headers-3.8.130bone70
E: Couldn't find any package by regex 'kernel-headers-3.8.13-bone70'

$ sudo apt-get install kernel-headers
E: Unable to locate package kernel-headers

Try searching the cache for anything that might be what I'm looking for:

$ apt-cache search kernel | grep headers
$apt-cache search headers | grep bone70
linux-headers-3.8.13-bone70

Note: from above searches, I discovered that the cache had headers up to and probably past bone79.
trying again to get the source tree headers:

$ sudo apt-get install linux-headers-$(uname -r)

Worked great.

Download hello.c and Makefile from google cached version of this site (which seems to be not responding right now for some reason) http://www.cyberciti.biz/faq/add-remove-list-linux-kernel-modules/

Copy Makefile and hello.c to new folder under /home/debian, cd to folder, run 'make'. Compiled .ko file as promised.

Run the following commands. Kernel module seems to be installed, although there is an extra message in the /var/log/messages file saying: "hello: module license 'unspecified' taints kernel"

$ modinfo hello.ko
$ sudo insmod hello.ko
$ lsmod
$ rmmod hello
$ tail -f /var/log/messages

Pulled raw rtc-pcf8563.c file from https://github.com/jeffegg/beaglebone/tree/master/drivers/rtc and tried to put it in its own directory under /home/debian with the Makefile from the hello example, changing the name of the object to compile, got some compile errors. Specifically it doesn't like THIS_MODULE and the module property declarations at the end.

The makefile at https://github.com/jeffegg/beaglebone/tree/master/drivers/rtc has a bunch of options for compiling other things like rtc-lib.o, rtc-core.o, all of which seem like I might need them.

Looking at the linux headers directory that I downloaded earlier, I am surprised to find the exact same makefile under /usr/src/linux-headers-3.8.13-bone70/drivers/rtc!!!! This may indicate that I might be able to find the kernel module in the source tree and just build it after all. The question is how to get the source tree. After a lot of fiddling, trying:

$sudo apt-get install linux-source

This seems to be getting me the 3.2 source instead of the 3.8 for unknown reasons, but that might be sufficient to get a drivers build directory that matches the drivers header directory.

Duck Chases Man

Link for use on a rainy day:

https://www.youtube.com/watch?v=n5qE9W_b55I

dsPIC30F Blink LED

I needed to get up to speed fast on how to add a timer interrupt for an imporved blink routine for the LED hanging off of my microchip dsPIC30F4012 PIC. I planned to make something fancy, but first I just needed to figure out whether there were timer interrupts in this PIC (there are, in fact there are five, and they appear on the block diagram on the datasheet), how to configure them in my C program, and whether some where better than others to use. The last question hasn't been answered for me yet, there are hints that the first timer might be different, maybe that it is directly driven by the system clock and the other ones might be driven by the instruction clock, but at this point I don't care because all of the examples that I found online used the first timer and so that was what I used.

Here are the links that I pored over to get enough examples that I was able to build my own code. The hard part was figuring out what applied to my particular PIC and what was for a PIC that was sufficiently different that I couldn't use it:

This is a nice tutorial in that an LED blinker is first shown as terrible code (piles of for loops to create a delay), then an interrupt handler. However, for some reason the author seems to be using the interrupt handler to time the delay which seems odd since the LED blink code could well have just been in there too.http://www.electronics-base.com/projects/complete-projects/195-microchip-microcontroller-dspic30f4013-blink-led-example-using-timer-complete-project

The original question in this forum thread is hilariously badly written, and the answers are all also bad except for one, which is full of wisdom. It's also not for my PIC: http://www.microchip.com/forums/m840532.aspx

This is probably the best example; although not exactly like what I wanted to do, it's for a PIC30F, it shows setup code for the timer, it explains about the prescaler and other built-in settings and how to use them. It also shows blinks both with a timer interrupt and in a simple loop using the delightful __delay32 function which I immediately also read up on: https://batchloaf.wordpress.com/2012/04/12/simple-timer-1-interrupt-example-for-the-dspic30f4011/

Here's another post by the same guy that did the one above; it has the blink example in it, but more importantly it has a ton of stuff about setting up programming (albeit with a much earlier version of the IDE): https://batchloaf.wordpress.com/dspic30f4011_super_example/

Here's a little bit more about __delay32(): http://www.microchip.com/forums/m486992.aspx

here's another nice example, just an LED blinker using a timing interrupt, with another person's example of using all the setup parameters for the timer: https://batchloaf.wordpress.com/2010/12/05/timer-1-interrupt-example-for-the-dspic30f4011/

Here's a whole reference manual just for the PIC30 timers, but it's so wordy that I just couldn't fight through to any answers about what was different about the different timers! Also all of their example code is in assembly, which is only a little helpful for my need to do this in C: http://ww1.microchip.com/downloads/en/DeviceDoc/70059D.pdf

The first example in this very professional-looking tutorial is another LED blinker using Timer 1. All of the examples that I found used Timer 1. There was information about how it's possible to join Timers 2&3 or 4&5 to make 32-bit counter/timers, which made me wonder what happens if that's not what you want to do, another question about the other timers that I was too rushed to find the answer to: http://www.mikroe.com/chapters/view/52/chapter-4-timers/

Here's something that I found while trying to learn if the other timers get the system clock or the instruction clock. The question is actually about a PIC33, but for some reason one of the commenters thinks that it's about the PIC30 and answers accordingly. However, it is unclear once again if his answer applies only to the first timer or all of them: http://www.microchip.com/forums/m156502.aspx

Here's an example for a Timer 2 module, but it's for a PIC16, so is only slightly helpful for my case: http://www.pcbheaven.com/picpages/The_Timer_Modules_Timer2/

Another PIC16 Timer2 example. This one is interesting because it shows a IDE utility called "Code Configurator" which might be helpful to learn how to use: http://microchip.wikidot.com/8bit:mcctimer2

Some test slides from an online class that start some examples for a PIC30F: http://academic.eng.au.edu/~nott/nott/MicroClass/Lectures/7.pdf

A powerful collection of timer examples, including setup of a PIC30F timer2/timer3 combination to blink an LED, although I'm not sure why a 32 bit counter would be needed for a .5Hz blink: https://www.pantechsolutions.net/project-kits/user-guide-programming-in-c-for-dspic30f4011

Some nice timer and interrupt examples, but for a PIC24: http://www.kibacorp.com/First%20Experiments%20Part%202.pdf

Here is my final C code. It's fancy; the objective was to have a slow blink pattern with an option for triggering a single fast blink. I created a 8Hz timer interrupt and then used globals to count through a 64-state counter, defining the slow blink on as the lower 32 states and the slow blink off as the upper 32 states. If the timer interrupt wakes up and a request for a fast blink ("activity_request") is set, it figures out what the last on/off state was, then either starts on a series of interrupt-driven states that turn the LED off, then on, then off, or if it was already off it just turns it on and off. The resulting visual effect is exactly what I was looking for.

int timer_counter = 0;
int activity_lead_off = 0;
int activity_on = 0;
int activity_request = 0;
int led_is_on = 0;

// Timer 1 interrupt service routine for LED blinking algorithm
void __attribute__((__interrupt__, __auto_psv__)) _T1Interrupt(void)
{

if (activity_lead_off == 1){

SetLed();
led_is_on = 1;
activity_on = 1;
activity_lead_off = 0;

} else if (activity_on == 1) {

ClearLed();
led_is_on = 0;
activity_on = 0;

} else if (activity_request == 1) {

activity_request = 0;
if (led_is_on == 1){

ClearLed();
led_is_on = 0;
activity_lead_off = 1;

} else {

SetLed();
led_is_on = 1;
activity_on = 1;

}

} else {

if (timer_counter < 32){

SetLed();
led_is_on = 1;

} else {

ClearLed();
led_is_on = 0;

}

}
if (timer_counter < 63) {

timer_counter++;

} else {

timer_counter = 0;

}
// Clear Timer 1 interrupt flag
_T1IF = 0;

}

void SetActivity()
{

if (activity_on == 0) {

activity_request = 1;

}

}


int main()
{

// Initialize Timer 1 for 8 calls/second
// PR1 AND tckps ARE SET TO CALL INTERRUPT EVERY 125ms
// Period = PR1 * prescaler * Tcy.
// Some documentation indicates that Tcy is crystal clock period
// Clock crystal is 7.3728MHz, Tcy = 135.633 nsec
T1CON = 0; // Clear Timer 1
T1CONbits.TCKPS = 3; // Set Timer 1 Prescaler 1:256
PR1 = 3600; // Set Timer 1 Period
_T1IP = 1; // Set Timer 1 interrupt priority
_T1IF = 0; // Clear Time 1 interrupt flag
_T1IE = 1; // Enable Timer 1 interrupt
T1CONbits.TON = 1; // Turn on Timer 1

.
.
.

}

Globals in python

If your code is so bad that you're using globals, here's what you need to know:

Modules can read the global all they want, but the moment you set a value to it without first declaring in the module that it is a global, you're creating a local variable and not setting the global. Use the statement "global varname" in the code somewhere before the set. Modules which do not set it don't need this declaration. A reference: