I have been working on stuff in latex recently and wanted something to trigger regeneration of pdfs without manual intervention. At first I thought about doing so in a loop every so often, but it didn't seem like the best approach.

Knowing about the cool kqueue framework I looked to see if there was a utility to watch files for me. I found the wait_on command via a FreeBSD forums post.

The wait on command will wait until the watched file has been changed and then exit. It is meant to be used within a loop. I through this together in zsh. Now when I :wq in vim wait on exists and my document rebuilds, evinces picks up on this and refreshes the display.

$ while true; do wait_on pres.tex; xelatex pres.tex; sleep 5; done

I have the sleep at the end to stop the document being built too often.

I have just finished reading Cryptonomicon , without any spoilers I can say that at a certain point a character controls the led's on his keyboard. This morning I found the kbdled utility via a forum post. It looks like a nice simple way to make the keyboard do something useful.

As I write this there are not any packages available for FreeBSD arm. That means on the Raspberry Pi I have to build the things I need from ports. Ports gives a lot of control about how the software is built, but right now I just want the tools I need installed.

It is hard to set up ports to install a collection of tools in a oner, but we can use portmaster to do this for us. The Pi is quite slow and will take a long time to build a small number of tools and their dependencies.

Normally portmaster will prompt for configuration for each package as it builds, it will then build a list of packages and prompt again to install these. The following line will install the listed tools without any prompting.

$ portmaster -mBATCH=yes --no-confirm -y sysutils/tmux editors/vim

• The -m flag will pass options to make
• --no-confirm will disable the 'install' prompt
• -y will answer yes to any prompts

I finally got all the components to use the bag of electret microphones I got last year. Using a LM36 audio amp I set up a simple circuit to read values from the microphone and set LED's corresponding to the value read.

I had trouble finding a solid example of doing analog reads in a loop for the msp430. This program, sets up LED's(On P1.1 and P1.6), sets up the ADC, then sits in a loop. If the value on the ADC is grater than 512 the LED will go red.

I tested this by shouting at the micro controller, something I have done many times before, but never with such satisfying results.

#include <msp430g2553.h>

unsigned int adcvalue = 0;

void configureADC(void);

int
main(void)
{
    WDTCTL = WDTPW + WDTHOLD;       //Stop the Watch dog

    P1DIR |= 0x41;                  //Enabled P1.0 and P1.6
    P1OUT = 0x41;

    BCSCTL1 = CALBC1_1MHZ;          //Set range
    BCSCTL2 &= CALBC1_1MHZ;         //SMCLK = DCO = 1MHz

    P1SEL |= BIT3;

    configureADC();
    __enable_interrupt();

    while(1) {
        __delay_cycles(20000);
        ADC10CTL0 |= ENC + ADC10SC;         //Sampling and conversion start
        adcvalue = ADC10MEM;                //Read from the ADC

        if(adcvalue > 512)
            P1OUT = 0x40;
        else
            P1OUT = 0x01;

    }

    return 0;
}

void
configureADC(void)
{
    ADC10CTL1 = INCH_3 + ADC10DIV_3;
    ADC10CTL0 = SREF_0 + ADC10SHT_3 + ADC10ON + ADC10IE;
    ADC10AE0 |= BIT3;
}

The cool thing we get with the msp430 and the Launchpad is on chip debugging. This goes a long way to pave over the warts of writing straight C for the 430. We will load up the blink program from last time , run it with the debugger and pause execution.

Start up mspdebug as before, this time we pass a command for mspdebug to run directly. The "gdb" command will cause mspdebug to listen on port 2000, gdb can then connect and control the debugger.

$ mspdebug rf2500 "gdb"

Next we are going to start up msp430-gdb, load the program from before and start it running.

$ msp430-gdb
(gdb) target remote localhost:2000
(gdb) file led.elf
(gdb) load led.elf
(gdb) continue
^C
(gdb) break main.c:14
(gdb) c                 #We can shorthand commands
Now between each continue we will see the LED's toggle, red then green.
(gdb) continue

From gdb we can send mspdebug directly with the monitor command.