Merge pull request #7716 from MateuszMaz/#issue5119_pwm_fix

Fix issue #5119, changed pwmout_api.

Author: Cruz Monrreal

targets/TARGET_Freescale/TARGET_MCUXpresso_MCUS/TARGET_MCU_K64F/pwmout_api.c

@@ -124,8 +124,25 @@ void pwmout_period_us(pwmout_t* obj, int us)
     FTM_Type *base = ftm_addrs[obj->pwm_name >> TPM_SHIFT];
     float dc = pwmout_read(obj);
 
-    // Stop FTM clock to ensure instant update of MOD register
-    base->MOD = FTM_MOD_MOD((pwm_clock_mhz * (float)us) - 1);
+    uint32_t pwm_base_clock;
+    uint32_t clkdiv = 0;
+    pwm_base_clock = CLOCK_GetFreq(kCLOCK_BusClk);
+    pwm_clock_mhz = (float) pwm_base_clock / 1000000.0f;
+    uint32_t mod = (pwm_clock_mhz * (float) us) - 1;
+    while (mod > 0xFFFF) {
+        ++clkdiv;
+        pwm_clock_mhz /= 2.0f;
+        mod = (pwm_clock_mhz * (float) us) - 1;
+        if (clkdiv == 7) {
+            break;
+        }
+    }
+    uint32_t SC = base->SC & ~FTM_SC_PS_MASK;
+    SC |= FTM_SC_PS((ftm_clock_prescale_t) clkdiv);
+    base->SC = SC;
+
+    //Stop FTM clock to ensure instant update of MOD register
+    base->MOD = FTM_MOD_MOD(mod);
     pwmout_write(obj, dc);
 }