1 | /* |
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2 | * This routine is a simple spin delay |
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3 | * |
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4 | * Author: Ralf Corsepius (corsepiu@faw.uni-ulm.de) |
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5 | * |
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6 | * COPYRIGHT (c) 1999, Ralf Corsepius, Ulm, Germany |
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7 | * |
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8 | * This program is distributed in the hope that it will be useful, |
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9 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
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10 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. |
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11 | * |
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12 | * |
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13 | * COPYRIGHT (c) 1989-1999. |
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14 | * On-Line Applications Research Corporation (OAR). |
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15 | * |
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16 | * The license and distribution terms for this file may be |
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17 | * found in the file LICENSE in this distribution or at |
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18 | * http://www.OARcorp.com/rtems/license.html. |
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19 | * |
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20 | * $Id$ |
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21 | */ |
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22 | |
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23 | |
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24 | #include <rtems.h> |
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25 | |
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26 | /* |
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27 | * Simple spin delay in microsecond units for device drivers. |
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28 | * This is very dependent on the clock speed of the target. |
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29 | * |
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30 | * Since we don't have a real time clock, this is a very rough |
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31 | * approximation, assuming that each cycle of the delay loop takes |
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32 | * approx. 4 machine cycles. |
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33 | * |
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34 | * e.g.: clicks_per_second = 20MHz |
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35 | * => 5e-8 secs per instruction |
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36 | * => 4 * 5e-8 secs per delay loop |
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37 | */ |
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38 | |
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39 | void CPU_delay( unsigned32 microseconds ) |
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40 | { |
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41 | register unsigned32 clicks_per_usec = |
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42 | rtems_cpu_configuration_get_clicks_per_second() / 1000000 ; |
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43 | register unsigned32 _delay = |
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44 | (microseconds) * (clicks_per_usec); |
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45 | asm volatile ( |
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46 | "0: add #-4,%0\n\ |
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47 | nop\n\ |
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48 | cmp/pl %0\n\ |
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49 | bt 0b\n\ |
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50 | nop" |
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51 | :: "r" (_delay) ); |
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52 | } |
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