main.cpp

00001 #include <mbed.h>
00002  
00003 #if 1
00004 #define DWT_CONTROL ((volatile uint32_t *)0xE0001000)
00005 #define DWT_CYCCNT  ((volatile uint32_t *)0xE0001004)
00006 #define SCB_DEMCR   ((volatile uint32_t *)0xE000EDFC)
00007 
00008 static inline uint32_t getDwtCyccnt(void)
00009 {
00010     return *DWT_CYCCNT;
00011 }
00012 
00013 static inline void resetDwtCyccnt(void)
00014 {
00015     *DWT_CYCCNT = 0; // reset the counter
00016 }
00017 
00018 static inline void enableDwtCyccnt(void)
00019 {
00020     *SCB_DEMCR = *SCB_DEMCR | (1u << 24); // TRCENA = 1
00021     *DWT_CONTROL = *DWT_CONTROL | 1 ; // enable the counter (CYCCNTENA = 1)
00022     *DWT_CYCCNT = 0; // reset the counter
00023 }
00024 
00025 #endif
00026 
00027 Serial pc(USBTX, USBRX);
00028 
00029 static void benchmark_wait_us() {
00030     uint32_t count[11];
00031     enableDwtCyccnt();
00032     resetDwtCyccnt();
00033     count[0] = getDwtCyccnt();
00034     wait_us(1000);
00035     count[1] = getDwtCyccnt();
00036     wait_us(1000);
00037     count[2] = getDwtCyccnt();
00038     wait_us(1000);
00039     count[3] = getDwtCyccnt();
00040     wait_us(1000);
00041     count[4] = getDwtCyccnt();
00042     wait_us(1000);
00043     count[5] = getDwtCyccnt();
00044     wait_us(1000);
00045     count[6] = getDwtCyccnt();
00046     wait_us(1000);
00047     count[7] = getDwtCyccnt();
00048     wait_us(1000);
00049     count[8] = getDwtCyccnt();
00050     wait_us(1000);
00051     count[9] = getDwtCyccnt();
00052     wait_us(1000);
00053     count[10] = getDwtCyccnt();
00054 
00055     for (size_t i = 0; i <= 10; i++) {
00056         const uint32_t diff = (i >= 1)?(count[i] - count[i - 1]):0;
00057         pc.printf("%d (%d)\r\n", count[i], diff);
00058     }
00059 }
00060 
00061 static void benchmark_nop() {
00062     uint32_t count[11];
00063     enableDwtCyccnt();
00064     resetDwtCyccnt();
00065     count[0] = getDwtCyccnt();
00066     __nop();
00067     count[1] = getDwtCyccnt();
00068     __nop();
00069     count[2] = getDwtCyccnt();
00070     __nop();
00071     count[3] = getDwtCyccnt();
00072     __nop();
00073     count[4] = getDwtCyccnt();
00074     __nop();
00075     count[5] = getDwtCyccnt();
00076     __nop();
00077     count[6] = getDwtCyccnt();
00078     __nop();
00079     count[7] = getDwtCyccnt();
00080     __nop();
00081     count[8] = getDwtCyccnt();
00082     __nop();
00083     count[9] = getDwtCyccnt();
00084     __nop();
00085     count[10] = getDwtCyccnt();
00086 
00087     for (size_t i = 0; i <= 10; i++) {
00088         const uint32_t diff = (i >= 1)?(count[i] - count[i - 1]):0;
00089         pc.printf("%d (%d)\r\n", count[i], diff);
00090     }
00091 }
00092 
00093 int main() {
00094     pc.baud(115200);
00095     pc.printf("CPU SystemCoreClock is %.2f MHz\r\n", (float)SystemCoreClock/1000.0f/1000.0f);
00096     pc.printf("Nucleo compare DWT_CYCCNT to wait_us\r\n");
00097 
00098     //
00099     benchmark_wait_us();
00100     benchmark_nop();
00101 }
00102