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exact delay cycles in freeRTOS task

Posted by jradoslav on June 12, 2014

Hi All

I have implemented task with software USART receiver where is call USARTbitdelay routine. This routine is implemented with delayus OR delayns based on delay_cycles(count) delay have to be exact tick count but these routine consumes task running state time.

~~~~~~~ void readByte() { uses 8x bit delay function delay_cycles in ASF framework, how can be implemented in FreeRtos delay alternative? } void task() {

while(1)
{ 
     readByte(); // function consume running state and other tasks are blocked
}

}

~~~~~~~

how can i implement next:

block task BitDelay unblock task

or

freertosBitDelay()

thank you


exact delay cycles in freeRTOS task

Posted by bowerymarc on June 12, 2014

Looks like you’re using bit delay for sampling, so they have to be pretty precise, and I’m guessing pretty fast, much faster than 1mS. I’d suggest using a timer with an interrupt, set the timer to the sample period you want, and grab the bit there. Keep some static variables so when you accumulate a byte, you could push it into a queue and use the queue as your blocking mechanism.

On Jun 12, 2014, at 2:17 PMEDT, Radoslav Jízdný jradoslav@users.sf.net wrote:

Hi All

I have implemented task with software USART receiver where is call USARTbitdelay routine. This routine is implemented with delayus OR delayns based on delay_cycles(count) delay have to be exact tick count but these routine consumes task running state time.

void readByte() { uses 8x bit delay function delay_cycles in ASF framework, how can be implemented in FreeRtos delay alternative? } void task() {

while(1)
{ 
     readByte(); // function consume running state and other tasks are blocked
}

} how can i implement next:

block task BitDelay unblock task

or

freertosBitDelay()

thank you

exact delay cycles in freeRTOS task

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exact delay cycles in freeRTOS task

Posted by heinbali01 on June 12, 2014

Hi Radoslav,

Yes same idea: install a timer interrupt, which takes RX samples at fixed intervals. If the baudrate is 9600, the interrupt rate should be 3 to 5 times faster: 28.8 or 48 Khz.

If you want to make your timer interrupt 'lighter', you could put the samples in a circular buffer with a head and a tail pointer: the head for writing samples (from the interrupt) and the tail for reading them (from your task).

And as soon as you see a stable high (e.g. 8 bit times), you might want to call xSemaphoreGiveFromISR(), so your task will be woken up to process the received data.

A second method is installing a GPIO interrupt on the RX pin. When the interrupt fires you could register the current time and the RX value. This needs a high precision time, for instance the COUNT value of a fast running clock.

I have used both methods successfully. The GPIO interrupt gives a lower CPU load of course, but it is a bit more difficult to analyse the data.

Regards, Hein


exact delay cycles in freeRTOS task

Posted by jradoslav on June 12, 2014

this sequential code is OK tested

~~~~~~

uint32_t bitDelayNS = 1000000000/baudRate;

int bcount = 8;

while(ioportgetpin_level(pin));

delay_ns(bitDelayNS>>1);

while(bcount--) { delayns(bitDelayNS); *recByte >>= 1; if(ioportgetpinlevel(pin)) *recByte |= 0x80; } delay_ns(bitDelayNS);

~~~~~~

here is coded under itnerupt but bytes sent by stdio is corupted. timer is configured 10x faster half bit delay baud rate is 4800

~~~~~~

define TC TC0
define CHANNEL 0
define IDTC IDTC0
define TCHandler TC0Handler
define TCIRQn TC0IRQn

ioportpint pin;

main() {

setpinAdr(&pin);

    printf("INIT OK\r\n");
tc_config(96000); //periode is set 10*(half bit delay)

   // Configure TC interrupts
NVIC_DisableIRQ(TC_IRQn);
NVIC_ClearPendingIRQ(TC_IRQn);
NVIC_SetPriority(TC_IRQn,0);
NVIC_EnableIRQ(TC_IRQn);

while(1);

}

define WAIT(n) (n*10)

void TC_Handler(void) {

 uint32_t dummy;
   dummy = tc_get_status(TC,CHANNEL);
   UNUSED(dummy);


   if(usartState == 0)
   {
	   if(ioport_get_pin_level(pin))
	   {
		 ioport_toggle_pin_level(LED3_PIO);
		 usartState = 1;

		 cntBits = WAIT(3); //3 x 0.5 delay
		 bcount = 8;
	   }
   }
   cntBits--;

   if(usartState > 0 && !cntBits)
   {

	 switch(usartState)
	 {


		 case 1:
		 {
			if(bcount)
			{
				 recByte >>= 1;
				 if(ioport_get_pin_level(pin))
					  recByte |= 0x80;

				 cntBits = WAIT(2); // 1 bit delay 
				 --bcount;
			}
			else
			{
				 putchar(recByte);
				 cntBits = WAIT(2);
				 usartState = 2;
			}

		 }
		 break;
		 case 2:
			 usartState = 0;
			 break;

	 }

   }

}

// Configuration function for the Timer. static void tcconfig(uint32t freqdesired) { // INPUTS: // freqdesired The desired rate at which to call the ISR, Hz.

uint32t uldiv; uint32t ultcclks; uint32t ulsysclk = sysclkgetcpuhz(); uint32t counts;

// Configure PMC pmcenableperiphclk(IDTC);

// Configure TC for a 4Hz frequency and trigger on RC compare. tcfindmckdivisor( (uint32t)freqdesired, // The desired frequency as a uint32. ulsysclk, // Master clock freq in Hz. &uldiv, // Pointer to register where divisor will be stored. &ultcclks, // Pointer to reg where clock selection number is stored. ulsysclk); // Board clock freq in Hz. tcinit(TC0, CHANNEL, ultcclks | TCCMR_CPCTRG);

// Find the best estimate of counts, then write it to TC register C. counts = (ulsysclk/uldiv)/freqdesired; tcwrite_rc(TC0, 0, counts);

// Enable interrupts for this TC, and start the TC. tcenableinterrupt(TC, CHANNEL, TCIERCPCS); // Enable interrupt. tc_start(TC,CHANNEL); // Start the TC.

}

~~~~~~


exact delay cycles in freeRTOS task

Posted by heinbali01 on June 13, 2014

Hi Radoslav,

Your interrupt is not yet implemented the way it can work.

I attached a bit of code which isn't perfect but it might give more ideas.

Regards, Hein

Attachments

tc_usart.c (3459 bytes)

exact delay cycles in freeRTOS task

Posted by jradoslav on June 13, 2014

thank you Hein

I have coded finall version of Software UART based on interrupts. edge detection start bit + timer counter that counter periode is max half delay of bit, freq = 2*baudrate Hz.

it is enough to call the handler 2 times for 1 bit sampling, without any while waiting. After receiving 1 byte timer counter is disabled and edge detecotor enabled.

57600 baud rate on 84Mhz sam3x was ok.

code has no error detection.

here is core: complete code is attached

~~~~~~

typedef enum { eRS2322400 = 2400, eRS2324800 = 4800, eRS2329600 = 9600, eRS23219200 = 19200, eRS23238400 = 38400, eRS23257600 = 57600, eRS232_115200 = 115200,

}RS232Baud_t;

typedef struct structSWIRs232 { RS232Baudt rs232Baud; void (receiveByte)(char); Pio pio; uint32t pinNum; uint32t PIOID; IRQnType PIOIRQn;

}RS232SWIt; void rs232intreceiverinit(RS232SWIt* rs232); void rs232intreceiverenable(RS232SWIt* rs232); void rs232intreceiverdisable(RS232SWI_t* rs232);

///core

void pinfallingedgehandler(uint32t a,uint32_t b) {

 pio_disable_interrupt(rs232base->pio, (1u<<rs232base->pinNum));
 halfBitDelayCount = 3; //wait 1.5 bit
 bitCount = 8;
 usartState = 1;
 tc_start(TC,CHANNEL); //reset counter

}

void TC_Handler(void) {

 uint32_t ul_status= tc_get_status(TC,CHANNEL);

 UNUSED(ul_status);

   if(!(--halfBitDelayCount))
	   switch(usartState)
	   {
		   case 1:

				 recByte >>= 1;//ROR

				 if(pio_get(rs232base->pio ,rs232base->PIO_ID, (1u<<rs232base->pinNum)))
					  recByte |= 0x80; //CARRY bit

				 if(!(--bitCount))
					 usartState = 2;//wait stop bit

				 halfBitDelayCount = 2; //wait 1 bit

			   break;
		  case 2:

			  	  //stop bit level is high
			   	   usartState = 0;
			   	   tc_stop(TC,CHANNEL);
			   	   rs232base->receiveByte(recByte);// send to buffer management
			   	   pio_enable_interrupt(rs232base->pio, (1u<<rs232base->pinNum)); //wait for falling edge


		  break;
	   }

}

~~~~~~

Attachments

rs232.c (3773 bytes)
rs232.h (966 bytes)

exact delay cycles in freeRTOS task

Posted by jradoslav on June 13, 2014

~~~~~ //initialization

RS232SWIt config = { .rs232Baud = 57600, .pio = PIOA, .pinNum = 26, .PIOID = IDPIOA, .PIOIRQn = PIOA_IRQn, .receiveByte = &receiveByte

};

rs232_int_receiver_init(&config);
rs232_int_receiver_enable(&config);

~~~~~


exact delay cycles in freeRTOS task

Posted by heinbali01 on June 13, 2014

Hi Radoslav,

That looks great, good work!

It's a good idea to use a GPIO interrupt on a falling edge to start the TC timer for recognition, and switch it off at the stop bit. Now it syncs on the start-bit, which should be good enough in most cases.

I made my algorithm to recognise a continuous stream of rs232 data from devices with a less precise clock and also for lower-quality hardware ( I want to be able to inform the hardware people and say: look at these errors! Otherwise software always gets the blame of a failure )

One remark: when you assign "usartState = 2", you might want to "fall through" and stop the TC immediately, in order not the miss the GPIO interrupt of the next start bit?

TC interrupts may come too late, but never too early.

Wish you good luck,

Hein


exact delay cycles in freeRTOS task

Posted by jradoslav on June 13, 2014

Thank you Hein

I think , the error detection can be implemented on higher layer (checksumm etc.),

last stop bit delay is probably nessesary , because pinfallingedge_handler can raise on last data bit. time-moment for pin reading is exactly in half periode of pin level state:

state time element:

t0>----reading T/2----<t1 , T = 1s/BaudRate,

this time-read-position is set by first 1,5T delays from start bit.

edge handler raise at time moment = (t0 state start bit) + few const cycles = C and C << T. C is time for edge detection processing + handler subroutine call instructions.


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