Revision 0:41971777e42c, committed 2015-04-26

Comitter:

discypus

Date:

Sun Apr 26 12:51:13 2015 +0000

Commit message:

Cortex-M DWT CYCCNT example;

Changed in this revision

diff -r 000000000000 -r 41971777e42c main.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Sun Apr 26 12:51:13 2015 +0000
@@ -0,0 +1,102 @@
+#include <mbed.h>
+ 
+#if 1
+#define DWT_CONTROL ((volatile uint32_t *)0xE0001000)
+#define DWT_CYCCNT  ((volatile uint32_t *)0xE0001004)
+#define SCB_DEMCR   ((volatile uint32_t *)0xE000EDFC)
+
+static inline uint32_t getDwtCyccnt(void)
+{
+    return *DWT_CYCCNT;
+}
+
+static inline void resetDwtCyccnt(void)
+{
+    *DWT_CYCCNT = 0; // reset the counter
+}
+
+static inline void enableDwtCyccnt(void)
+{
+    *SCB_DEMCR = *SCB_DEMCR | (1u << 24); // TRCENA = 1
+    *DWT_CONTROL = *DWT_CONTROL | 1 ; // enable the counter (CYCCNTENA = 1)
+    *DWT_CYCCNT = 0; // reset the counter
+}
+
+#endif
+
+Serial pc(USBTX, USBRX);
+
+static void benchmark_wait_us() {
+    uint32_t count[11];
+    enableDwtCyccnt();
+    resetDwtCyccnt();
+    count[0] = getDwtCyccnt();
+    wait_us(1000);
+    count[1] = getDwtCyccnt();
+    wait_us(1000);
+    count[2] = getDwtCyccnt();
+    wait_us(1000);
+    count[3] = getDwtCyccnt();
+    wait_us(1000);
+    count[4] = getDwtCyccnt();
+    wait_us(1000);
+    count[5] = getDwtCyccnt();
+    wait_us(1000);
+    count[6] = getDwtCyccnt();
+    wait_us(1000);
+    count[7] = getDwtCyccnt();
+    wait_us(1000);
+    count[8] = getDwtCyccnt();
+    wait_us(1000);
+    count[9] = getDwtCyccnt();
+    wait_us(1000);
+    count[10] = getDwtCyccnt();
+
+    for (size_t i = 0; i <= 10; i++) {
+        const uint32_t diff = (i >= 1)?(count[i] - count[i - 1]):0;
+        pc.printf("%d (%d)\r\n", count[i], diff);
+    }
+}
+
+static void benchmark_nop() {
+    uint32_t count[11];
+    enableDwtCyccnt();
+    resetDwtCyccnt();
+    count[0] = getDwtCyccnt();
+    __nop();
+    count[1] = getDwtCyccnt();
+    __nop();
+    count[2] = getDwtCyccnt();
+    __nop();
+    count[3] = getDwtCyccnt();
+    __nop();
+    count[4] = getDwtCyccnt();
+    __nop();
+    count[5] = getDwtCyccnt();
+    __nop();
+    count[6] = getDwtCyccnt();
+    __nop();
+    count[7] = getDwtCyccnt();
+    __nop();
+    count[8] = getDwtCyccnt();
+    __nop();
+    count[9] = getDwtCyccnt();
+    __nop();
+    count[10] = getDwtCyccnt();
+
+    for (size_t i = 0; i <= 10; i++) {
+        const uint32_t diff = (i >= 1)?(count[i] - count[i - 1]):0;
+        pc.printf("%d (%d)\r\n", count[i], diff);
+    }
+}
+
+int main() {
+    pc.baud(115200);
+    pc.printf("CPU SystemCoreClock is %.2f MHz\r\n", (float)SystemCoreClock/1000.0f/1000.0f);
+    pc.printf("Nucleo compare DWT_CYCCNT to wait_us\r\n");
+
+    //
+    benchmark_wait_us();
+    benchmark_nop();
+}
+ 
\ No newline at end of file

diff -r 000000000000 -r 41971777e42c mbed.bld
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed.bld	Sun Apr 26 12:51:13 2015 +0000
@@ -0,0 +1,1 @@
+http://mbed.org/users/mbed_official/code/mbed/builds/433970e64889
\ No newline at end of file