Overview

This section details the specific for using DUKtape on Cortex-M4 processor. In this case we select Tiva-C microcontroller.

Linker File

The Linker file is responsible to accommodate the produced executable in the target processor. It shall match the memory map specifications of the target device. For the case Tiva-C (TM4C129N), select the mem.ld file and modify as shown below.

Targeting Peripherals is the same as with Cortex-M3

Timer Setup

As with the Cortex-M3, we used on of the built-in timers to implement the gettimeof day function. The specifics are:

The peripheral frequency on the Tiva-C for timers was selected to be 16Mhz and the timers have the capability to define a prescaler, so we can set it up to have a tick of 1us and then and ISR that update a variable called seconds.
The limitation is that when timers are used separately, they are 16-bits and the prescaler is only 8-bits. Doing the math:

Tq = 1/16Mhz = 62.5uS
Prescaler = 245
Tq_w_prescaler = 245 * 62.5uS = 0.0153s

To get 1s = 1/Tq_w_prescaler = 65306 steps

[$[Get Code]]

Tiva-C counter is set to go in the down direction to have a true-prescaler behavior, so it will be necessary to subtract the top values calculated and then multiplied them by Tq.

The function gettimeofday is implemented as follows:

int _gettimeofday(struct timeval *tv, void *tz)
{
unsigned long i,j;
tv->tv_sec = sysSeconds;

i = (65306 - (TIMER1->TAV & 0x00FFFF));
i *= 15312; // Every count from prescaler = 0.0153125

// Taking the remains from prescaler
j = ((TIMER1->TAV & 0xFF0000) >> 16);
j = 245-j;
j *= 62;
tv->tv_usec = i+j;

return(0);
}

[$[Get Code]]

Duktape Event Example

This example consist on toggling a LED every 3 seconds using DUKtape.

/*
* Simple LED time test.
*/

function main() {

setInterval(function () {
LedControl.toggle(2);
}, 3000);
}

main();

[$[Get Code]]

The result operation is shown below

Duktape Eclipse ARM Cortex M4

Overview

Linker File

Timer Setup

Duktape Event Example

See Also