[KL25Z] Improve division by constant integer in us_ticker implementation.

libraries/mbed/vendor/Freescale/capi/us_ticker.c

@@ -69,7 +69,18 @@ uint32_t us_ticker_read() {
     uint64_t ticks;
     ticks  = (uint64_t)PIT->LTMR64H << 32;
     ticks |= (uint64_t)PIT->LTMR64L;
-    ticks  = (~ticks) / 24;
+    
+    // More efficient division by constant integer (24): /8 /3
+    // complement (because count down timer) and divide by 8
+    ticks  = (~ticks) >> 3;
+    
+    // divide by 3
+    if (ticks > 0xFFFFFFFF) {
+        ticks /= 3;
+    } else {
+        ticks = (ticks * 0x55555556) >> 32;
+    }
+    
     return (uint32_t)(0xFFFFFFFF & ticks);
 }
 

libraries/tests/mbed/div/main.cpp

@@ -0,0 +1,27 @@
+#include "mbed.h"
+
+uint32_t test_64(uint64_t ticks) {
+    ticks >>= 3; // divide by 8
+    if (ticks > 0xFFFFFFFF) {
+        ticks /= 3;
+    } else {
+        ticks = (ticks * 0x55555556) >> 32; // divide by 3
+    }
+    return (uint32_t)(0xFFFFFFFF & ticks);
+}
+
+int main() {
+    // 0xFFFFFFFF *  8 =  0x7fffffff8
+    printf("expected        : 55555555\n");
+    printf("64:  0x7fffffff8: %x\n", test_64(0x7fffffff8));
+    
+    // 0xFFFFFFFF * 24 = 0x17ffffffe8
+    printf("expected        : ffffffff\n");
+    printf("64: 0x17ffffffe8: %x\n", test_64(0x17FFFFFFE8));
+    
+    DigitalOut led(LED1);
+    while (1) {
+        led = !led;
+        wait(0.5);
+    }
+}

workspace_tools/make.py

@@ -88,7 +88,7 @@ if __name__ == '__main__':
             copy(bin, options.disk)
         
         if options.serial:
-            if options.mcu in ["M0+", "LPC812"]:
+            if options.mcu in ["KL25Z", "LPC812"]:
                 # We do not have a flash disk where to store the image, we write
                 # it directly on the target chip, therefore we need to
                 # disconnect the interface: wait for the device to enumerate

workspace_tools/tests.py

@@ -296,6 +296,12 @@ TESTS = [
         "source_dir": join(TEST_DIR, "mbed", "time_us"),
         "dependencies": [MBED_LIBRARIES, TEST_MBED_LIB],
     },
+    {
+        "id": "MBED_26", "description": "MBED: Integer constant division",
+        "source_dir": join(TEST_DIR, "mbed", "div"),
+        "dependencies": [MBED_LIBRARIES, TEST_MBED_LIB],
+    },
+    
     # CMSIS RTOS tests
     {
         "id": "CMSIS_RTOS_1", "description": "CMSIS RTOS: Basic",