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change_latency.c
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1 /*
2  * "Copyright (c) 2008 Robert B. Reese, Bryan A. Jones, J. W. Bruce ("AUTHORS")"
3  * All rights reserved.
4  * (R. Reese, reese_AT_ece.msstate.edu, Mississippi State University)
5  * (B. A. Jones, bjones_AT_ece.msstate.edu, Mississippi State University)
6  * (J. W. Bruce, jwbruce_AT_ece.msstate.edu, Mississippi State University)
7  *
8  * Permission to use, copy, modify, and distribute this software and its
9  * documentation for any purpose, without fee, and without written agreement is
10  * hereby granted, provided that the above copyright notice, the following
11  * two paragraphs and the authors appear in all copies of this software.
12  *
13  * IN NO EVENT SHALL THE "AUTHORS" BE LIABLE TO ANY PARTY FOR
14  * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT
15  * OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF THE "AUTHORS"
16  * HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
17  *
18  * THE "AUTHORS" SPECIFICALLY DISCLAIMS ANY WARRANTIES,
19  * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
20  * AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
21  * ON AN "AS IS" BASIS, AND THE "AUTHORS" HAS NO OBLIGATION TO
22  * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS."
23  *
24  * Please maintain this header in its entirety when copying/modifying
25  * these files.
26  *
27  *
28  */
29 
30 #include "pic24_all.h"
31 
32 /** \file
33 Measure latency using change notification.
34 RB2 drives RB3 to generate an CN interrupt.
35 Need to run this with a slow clock to avoid
36 external loading effecting CN triggering point.
37 With FCY = 4 MHz, got 8 FYCs high period, 8 FYCs low period.
38 */
39 
40 //Interrupt Service Routine for Change Notification
41 void _ISRFAST _CNInterrupt (void) {
42  _LATB2 = 0; //set back low
43  NOP(); //give the CN time to propagate so
44  NOP(); //clearing the flag will actually clear it.
45  NOP();
46  _CNIF = 0; //clear the change notification interrupt bit
47 }
48 
49 int main (void) {
50  configBasic(HELLO_MSG);
51  /** PIO ***********/
52  CONFIG_RB2_AS_DIG_OUTPUT();
53  _LATB2 = 0;
54  CONFIG_RB3_AS_DIG_INPUT();
55  ENABLE_RB3_CN_INTERRUPT();
56  /** Configure Change Notification general interrupt */
57  _CNIF = 0; //Clear the interrupt flag
58  _CNIP = 2; //Choose a priority
59  _CNIE = 1; //enable the Change Notification general interrupt
60  while (1) {
61  _LATB2 = 1; //trigger interrupt by bringing high
62  NOP(); //give the CN time to propagate
63  NOP();
64  }
65 }