OMAP l-138 LCDK - GPIO and PWM

Pedro Freire

Hi experts,

I have an OMAP l-138 LCDK board running the linux kernel 3.3.0. So far, i already made and execute on the target board an hello world program using a text editor and the ti-sdk-omapl138-lcdk-01.00.00 on Ubuntu.

I would like to develop a small graphic application to control one LED with the board, and i would like to ask you for some guidance... I am completely lost, i have spend the hole day searching for examples, trying to create and execute a project in code composer, trying to compile some examples, but i haven't no success at all...

There's any example showing how to manipulate a GPIO pin? (I already have activated the GPIO option on the linux kernel menuconfig, under sys/classe/gpio i can see some of these pins)

And for PWM? (i have activated the corresponding option on the kernel menuconfig, but i cannot see any node under /sys/classes/pwm... the pwm modules shouldn't be there?)

If you could show me an example it will be great.

Thanks,
Pedro

over 7 years ago

0 Titus Stalin over 7 years ago

Expert 1180 points

Please refer to the below TI wiki pages.
processors.wiki.ti.com/.../Linux_PSP_GPIO_Driver_Guide
processors.wiki.ti.com/.../Configuring_GPIO_Interrupts

To control the LED, please do the below commands.
If the GPIO no is 30,
echo 30 > /sys/class/gpio/export
echo "out" > /sys/class/gpio/gpio30/direction
echo 1 > /sys/class/gpio/gpio30/value (glow the LED)
echo 0 > /sys/class/gpio/gpio30/value (OFF the LED)

For PWM support, please do make sure that you have the entry for PWM in board file.

0 Pedro Freire over 7 years ago in reply to Titus Stalin

Intellectual 470 points

Hi,

Thanks for your answer.

I already have configured the kernel's menuconfig in order to activate the GPIO and PWM functions.

GPIO:

I was able to teste the commands that you wrote for some pins. In order to test another pins i also modified the da850.c file, and here i have a question... I would like to activate the pin GP8[2], but when i tried to add the command MUX_CFG(DA850, GPIO8_2, 3, 24, 15, 4, false), the compiler says that GPIO8_2 is undeclared... It's impossible to select this pin?

I tried to create a program to use the gpio driver commands on a C program, but the compiler doesn't recognise the include <linux/gpio.h>, do i need to install something on my linux host machine?

PWM:

I couldn't get any pwm node under /sys/class/pwm...

Thanks a lot,

Pedro

0 Titus Stalin over 7 years ago in reply to Pedro Freire

Expert 1180 points

GPIO:

I was able to teste the commands that you wrote for some pins. In order to test another pins i also modified the da850.c file, and here i have a question... I would like to activate the pin GP8[2], but when i tried to add the command MUX_CFG(DA850, GPIO8_2, 3, 24, 15, 4, false), the compiler says that GPIO8_2 is undeclared... It's impossible to select this pin?

You have to add the entry in "arch/arm/mach-davinic/include/mach/mux.h

Append into this enum structure.
enum davinci_da850_index {
...........
...........
DA850_GPIO8_2,
};

0 Pedro Freire over 7 years ago in reply to Titus Stalin

Intellectual 470 points

Thanks for your answer :)

Do you know why i am not getting anything under /sys/class/pwm? I saw some posts describing that problem but didn't find any solution :/

Thanks,
Pedro

0 Titus Stalin over 7 years ago in reply to Pedro Freire

Expert 1180 points

Can you please attach your linux boot log (dmesg) ?

Regards,
Titus S.

0 Titusrathinaraj Stalin over 7 years ago in reply to Pedro Freire

TI__Guru** 116100 points

Please refer to these posts.
e2e.ti.com/.../1246694
e2e.ti.com/.../329624

0 Pedro Freire over 7 years ago in reply to Titusrathinaraj Stalin

Intellectual 470 points

Hi Titus,

Thanks! I already wrote a kernel module to configure some GPIO pins.

I was trying to configure also the eHRPWM in this kernel module but i am not understanding which driver i should use... Could you please give me some ideas or some example?

Thanks,

Pedro

0 Titusrathinaraj Stalin over 7 years ago in reply to Pedro Freire

TI__Guru** 116100 points

Please refer to the below TI eHRPWM and eCAP drivers.
linux-kernel/drivers/pwm

0 Pedro Freire over 7 years ago in reply to Titusrathinaraj Stalin

Intellectual 470 points

Thanks, i was there yesterday trying to understand the code of the driver ehrpwm...

I am not understanding how to create this parameter: struct pwm_device *p

The structure of the parameter:
struct ehrpwm_pwm {
struct pwm_device pwm[NCHAN]; --->> Theres any documentation explaining all these parameters?
struct pwm_device_ops ops;
spinlock_t lock;
struct clk *clk;
void __iomem *mmio_base;
unsigned short prescale_val;
int irq[2];
struct et_int st_etint;
struct tz_int st_tzint;
};

The function that i need to call at first:
static int ehrpwm_pwm_request(struct pwm_device *p)
{
struct ehrpwm_pwm *ehrpwm = to_ehrpwm_pwm(p);
int chan;

chan = p - &ehrpwm->pwm[0];

p->tick_hz = clk_get_rate(ehrpwm->clk);
debug("\n The clk freq is %lu", p->tick_hz);
clk_enable(ehrpwm->clk);
ehrpwm_pwm_stop(p);

return 0;
}

Thanks,
Pedro

0 Pedro Freire over 7 years ago in reply to Pedro Freire

Intellectual 470 points

I really don't understand how to use those drivers... :(

0 Pedro Freire over 7 years ago in reply to Pedro Freire

Intellectual 470 points

Maybe it could be useful to someone, so here's how i did it with the linux/pwm/pwm.h driver of kernel 3.3.0:

struct pwm_device *pwm_dev;

...

/* Config PWM */
pwm_dev = pwm_request_byname("ehrpwm.1\:0","pwm_device");

int requested = pwm_is_requested(pwm_dev);
if(requested){
printk(KERN_INFO "PWM Requested!\n");
}

int error = pwm_set_period_ns(pwm_dev, period);
if(error){
printk(KERN_INFO "---Not possible to set period!\n");
}

error = pwm_set_duty_percent(pwm_dev, dutyCycle);
if(error){
printk(KERN_INFO "---Not possible to set duty cycle!\n");
}

error = pwm_start(pwm_dev);

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OMAP l-138 LCDK - GPIO and PWM