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annotate delay.c @ 40:a38003b97de6

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Use debug cycle counter to handle delays.
author Daniel O'Connor <darius@dons.net.au>
date Mon, 01 Apr 2013 20:06:03 +1030
parents 891841f5f785
children cecb0506f4b8
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1 #include <assert.h>
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2 #include <stdint.h>
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3 #include "stm32f10x.h"
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4 #include "delay.h"
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6 /* Sleep for nCount usec
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7 */
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8 void
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9 delay(uint32_t nCount) {
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10 uint32_t dly, cnt, clk_per_usec, max_dly;
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11 volatile uint32_t *DWT_CYCCNT = (uint32_t *)0xe0001004;
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13 __disable_irq();
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15 #ifdef SYSCLK_FREQ_72MHz
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16 clk_per_usec = 72;
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17 max_dly = (1<<31) / clk_per_usec; /* Really half the maximum (still ~30 seconds at 72MHz) */
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18 #else
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19 #error "Unknown clock frequency"
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20 #endif
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21 assert(nCount < max_dly);
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23 cnt = *DWT_CYCCNT; /* Get current cycle count */
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24 dly = nCount * clk_per_usec;
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25 dly += cnt; /* Compute cycle count to stop at */
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26 if (dly < cnt)
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27 /* Stop count wrapped, wait until the counter wraps around */
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28 while (*DWT_CYCCNT > cnt)
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29 ;
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30 /* Wait until we get to the stop count */
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31 while (*DWT_CYCCNT < dly)
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32 ;
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34 __enable_irq();
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35 }
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