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annotate delay.c @ 89:fc21fb5b171b default tip

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Make error message more useful
author Daniel O'Connor <darius@dons.net.au>
date Fri, 13 Mar 2015 11:39:59 +1030
parents cecb0506f4b8
children
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a38003b97de6 Use debug cycle counter to handle delays.
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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 #ifdef SYSCLK_FREQ_72MHz
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14 clk_per_usec = 72;
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15 max_dly = (1<<31) / clk_per_usec; /* Really half the maximum (still ~30 seconds at 72MHz) */
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16 #else
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17 #error "Unknown clock frequency"
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18 #endif
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19 assert(nCount < max_dly);
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20
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21 cnt = *DWT_CYCCNT; /* Get current cycle count */
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22 dly = nCount * clk_per_usec;
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23 dly += cnt; /* Compute cycle count to stop at */
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24 if (dly < cnt)
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25 /* Stop count wrapped, wait until the counter wraps around */
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26 while (*DWT_CYCCNT > cnt)
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27 ;
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28 /* Wait until we get to the stop count */
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29 while (*DWT_CYCCNT < dly)
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30 ;
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31 }
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