141 lines
4.8 KiB
C
141 lines
4.8 KiB
C
/* ----------------------------------------------------------------------------
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* ATMEL Microcontroller Software Support
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* ----------------------------------------------------------------------------
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* Copyright (c) 2008, Atmel Corporation
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*
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* - Redistributions of source code must retain the above copyright notice,
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* this list of conditions and the disclaimer below.
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*
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* Atmel's name may not be used to endorse or promote products derived from
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* this software without specific prior written permission.
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*
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* DISCLAIMER: THIS SOFTWARE IS PROVIDED BY ATMEL "AS IS" AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT ARE
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* DISCLAIMED. IN NO EVENT SHALL ATMEL BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
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* OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
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* EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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* ----------------------------------------------------------------------------
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*/
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//------------------------------------------------------------------------------
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// Headers
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//------------------------------------------------------------------------------
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#include "tc.h"
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//------------------------------------------------------------------------------
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// Global functions
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//------------------------------------------------------------------------------
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//------------------------------------------------------------------------------
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/// Configures a Timer Counter to operate in the given mode. Timer is stopped
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/// after configuration and must be restarted with TC_Start().
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/// to obtain the target frequency.
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/// \param pTc Pointer to an AT91S_TC instance.
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/// \param mode Operating mode.
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//------------------------------------------------------------------------------
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void TC_Configure(AT91S_TC *pTc, unsigned int mode)
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{
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// Disable TC clock
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pTc->TC_CCR = AT91C_TC_CLKDIS;
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// Disable interrupts
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pTc->TC_IDR = 0xFFFFFFFF;
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// Clear status register
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pTc->TC_SR;
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// Set mode
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pTc->TC_CMR = mode;
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}
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//------------------------------------------------------------------------------
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/// Starts the timer clock.
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/// \param pTc Pointer to an AT91S_TC instance.
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//------------------------------------------------------------------------------
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void TC_Start(AT91S_TC *pTc)
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{
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pTc->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;
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}
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//------------------------------------------------------------------------------
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/// Stops the timer clock.
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/// \param pTc Pointer to an AT91S_TC instance.
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//------------------------------------------------------------------------------
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void TC_Stop(AT91S_TC *pTc)
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{
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pTc->TC_CCR = AT91C_TC_CLKDIS;
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}
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//------------------------------------------------------------------------------
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/// Finds the best MCK divisor given the timer frequency and MCK. The result
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/// is guaranteed to satisfy the following equation:
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/// (MCK / (DIV * 65536)) <= freq <= (MCK / DIV)
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/// with DIV being the highest possible value.
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/// Returns 1 if a divisor could be found; otherwise returns 0.
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/// \param freq Desired timer frequency.
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/// \param mck Master clock frequency.
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/// \param div Divisor value.
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/// \param tcclks TCCLKS field value for divisor.
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//------------------------------------------------------------------------------
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unsigned char TC_FindMckDivisor(
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unsigned int freq,
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unsigned int mck,
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unsigned int *div,
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unsigned int *tcclks)
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{
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const unsigned int divisors[5] = {2, 8, 32, 128,
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#if defined(at91sam9260) || defined(at91sam9261) || defined(at91sam9263) \
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|| defined(at91sam9xe) || defined(at91sam9rl64) || defined(at91cap9)
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BOARD_MCK / 32768};
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#else
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1024};
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#endif
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unsigned int index = 0;
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// Satisfy lower bound
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while (freq < ((mck / divisors[index]) / 65536)) {
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index++;
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// If no divisor can be found, return 0
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if (index == 5) {
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return 0;
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}
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}
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// Try to maximise DIV while satisfying upper bound
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while (index < 4) {
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if (freq > (mck / divisors[index + 1])) {
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break;
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}
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index++;
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}
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// Store results
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if (div) {
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*div = divisors[index];
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}
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if (tcclks) {
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*tcclks = index;
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}
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return 1;
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}
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