pin multiplexing in SAMD21

[aliyesami]

the following code is used for PWM in SAMD21, can you please  tell me how it works ?

Code: [Select]

int main(void)
{
   
    SystemInit();
     PORT->Group[0].DIRSET.reg=PORT_PA19;
    PORT->Group[0].PINCFG[PORT_PA19].reg |= PORT_PINCFG_PMUXEN;
     PORT->Group[0].PMUX[PORT_PA19].bit.PMUXO = 4;
     
         
     PM->APBCMASK.reg |= PM_APBCMASK_TC3;
     
     GCLK->CLKCTRL.reg = GCLK_CLKCTRL_ID(27/*TC3_GCLK_ID*/) |
     GCLK_CLKCTRL_CLKEN | GCLK_CLKCTRL_GEN(0);
     
     TC3->COUNT8.CTRLA.reg =
     TC_CTRLA_MODE(TC_CTRLA_MODE_COUNT8_Val) |
     TC_CTRLA_WAVEGEN(TC_CTRLA_WAVEGEN_NPWM_Val) |
     TC_CTRLA_PRESCALER(TC_CTRLA_PRESCALER_DIV1_Val) |
     TC_CTRLA_PRESCSYNC(TC_CTRLA_PRESCSYNC_PRESC_Val);
     while (TC3->COUNT8.STATUS.bit.SYNCBUSY);
     
     TC3->COUNT8.CTRLC.bit.INVEN1=1;
      while (TC3->COUNT8.STATUS.bit.SYNCBUSY);
     
     TC3->COUNT8.CTRLC.bit.CPTEN1=1;
      while (TC3->COUNT8.STATUS.bit.SYNCBUSY);
     
     TC3->COUNT8.COUNT.reg = 0;
     while (TC3->COUNT8.STATUS.bit.SYNCBUSY);
     
     TC3->COUNT8.PER.reg = 255;
     while (TC3->COUNT8.STATUS.bit.SYNCBUSY);
     
     TC3->COUNT8.CC[1].reg = 100;
     while (TC3->COUNT8.STATUS.bit.SYNCBUSY);
     
     TC3->COUNT16.CTRLA.reg |= TC_CTRLA_ENABLE;
     while (TC3->COUNT8.STATUS.bit.SYNCBUSY);
    while (1)
    {
       
       
    }
}


[eddie0x7c3]

Code: [Select]

 
    PORT->Group[0].PMUX[PORT_PA19].bit.PMUXO = 4;


The Pmux index for that pin would be 9 NOT 19 (PORT_PA19 = 1u<<19)

Code: [Select]

Pmux [0]  = Pins 0 and 1
Pmux [1] = pins 2 and 3
Pmux [2] = pins 4 and 5
Pmux [3] = pins 6 and 7....... and so on.......
Bits 0 - 3  in the register are for even numbered pins and the last 4 bits are for odd numbered pins


so it should read

Code: [Select]

PORT->Group[0].PMUX[9].bit.PMUXO = 4

[ataradov]

Also, have a look at my starter project that include more intuitive macros for manipulating GPIO pins: https://github.com/ataradov/mcu-starter-projects/tree/master/samd21 and this file specifically https://github.com/ataradov/mcu-starter-projects/blob/master/samd21/hal_gpio.h

[ataradov]

Or more detailed:

1. Configure pin PA19 to be an output and connect it to the peripheral (PWM in this case) as opposed to the GPIO block.

Although this code looks incorrect:

Code: [Select]

     PORT->Group[0].DIRSET.reg=PORT_PA19;
    PORT->Group[0].PINCFG[PORT_PA19].reg |= PORT_PINCFG_PMUXEN;
     PORT->Group[0].PMUX[PORT_PA19].bit.PMUXO = 4;
I don't know what PORT_PA19 unrolls in ASF, but I assume it is (1 << 19). In this case it should read

Code: [Select]

     PORT->Group[0].DIRSET.reg=PORT_PA19;
    PORT->Group[0].PINCFG[19].reg |= PORT_PINCFG_PMUXEN;
     PORT->Group[0].PMUX[19 / 2].bit.PMUXO = 4;

Or, if you were to use my macros:

Code: [Select]

HAL_GPIO_PIN(PWM_OUT, A, 19) // Define a pin

HAL_GPIO_PWM_OUT_out(); // This is actually not necessary if you use XXX_pmuxen(), but I do it anyway for documentation purposes.
HAL_GPIO_PWM_OUT_pmuxen(PORT_PMUX_PMUXE_D_Val);


2.

Code: [Select]

     PM->APBCMASK.reg |= PM_APBCMASK_TC3;
Enable clock to the TC3.

3.

Code: [Select]

     GCLK->CLKCTRL.reg = GCLK_CLKCTRL_ID(27/*TC3_GCLK_ID*/) |
     GCLK_CLKCTRL_CLKEN | GCLK_CLKCTRL_GEN(0);
Configure TC3 to be clocked from generator 0.

4. Setup TC3 according to the requirements. The code is pretty self explanatory.

[westfw]

Man, this subject is getting useful (?) answers on at least three different forums.  I hope the O.P. puts together a final summary and posts it in each of them...

[eddie0x7c3]

qualitative research ... leads to quantitative research .


 O0 <-- they need a light colored fro

[ataradov]

Well, to be fair, here this question was asked because I redirect all people PMing me on AVRFreaks here, since that forum turned into unmanageable mess.

[acaball1]

Alex,
After successfully using your example I got a timer running PWM at 350KHz. With ASF & ATmel Start the maximum I could get was 13KHz.
Therefore, I'm now trying to learn bare metal programming. I've downloaded your mcu-starter-projects-master package from github. I'm using Atmel Studio 7.
My question is: Where can I find information on the library? There seems to be a lot of definitions and maybe functions already included.

[ataradov]

Where can I find information on the library?

There is no library. All the definitions are in header files and all the names and values correspond to the datasheet. So DS is your documentation. After some time you will be able to blindly write code, just assuming that things you need are defined.

The beauty of this approach is that it is applicable to all MCU vendors, unlike ASF and other manufacturer-supplied frameworks.

There seems to be a lot of definitions and maybe functions already included.

There are some useful basic functions (mostly abstractions for special instructions) defined in core_cm0plus.h, core_cmFunc.h and core_cmInstr.h. Those files contain good commentary and you can always go back to the manufacturer documentation for description on specific instruction.