From 03f4fbc2530071f145b2eb11a7651c93e6dc15e4 Mon Sep 17 00:00:00 2001
From: Joe Finney <joe@comp.lancs.ac.uk>
Date: Mon, 24 Oct 2016 15:56:05 +0100
Subject: [PATCH] Extend range of PWM and minor code optimisations

Corrected minor bug that prevented the use of long periods (beyond 500ms).
Updated timer instance to be const to allow compiler optimisation
minor code cleanups
---
 .../TARGET_NORDIC/TARGET_MCU_NRF51822/pwmout_api.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/targets/hal/TARGET_NORDIC/TARGET_MCU_NRF51822/pwmout_api.c b/targets/hal/TARGET_NORDIC/TARGET_MCU_NRF51822/pwmout_api.c
index ed24a9f..e3bce09 100644
--- a/targets/hal/TARGET_NORDIC/TARGET_MCU_NRF51822/pwmout_api.c
+++ b/targets/hal/TARGET_NORDIC/TARGET_MCU_NRF51822/pwmout_api.c
@@ -31,7 +31,7 @@
 #define TIMER_PRESCALER_MIN     4
 #define TIMER_PRESCALER_MAX     9
 
-static NRF_TIMER_Type *timer = NRF_TIMER2;
+static NRF_TIMER_Type* const timer = NRF_TIMER2;
 
 // PWM levels, both in absolute microseconds, and TIMER ticks (we cache both for simplicity and performance).
 static uint32_t pwm_us[PWM_CHANNELS] = {0};
@@ -66,13 +66,10 @@ void TIMER2_IRQHandler(void)
 
     // Disable this interrupt - it is needed only when PWM values change.
     timer->SHORTS = TIMER_SHORTS_COMPARE3_CLEAR_Msk;
-
     timer->INTENCLR = TIMER_INTENCLR_COMPARE3_Msk;
     timer->PRESCALER = pwm_prescaler;
     timer->CC[TIMER_PERIOD_CC] = pwm_period_ticks;
-
     timer->TASKS_START = 1;
-
     timer->EVENTS_COMPARE[TIMER_PERIOD_CC] = 0;
 }
 #ifdef __cplusplus
@@ -270,6 +267,7 @@ void pwmout_period_us(pwmout_t *obj, int us)
 {
     uint32_t p = 0x10000;
     int prescaler = TIMER_PRESCALER_MIN;
+    uint32_t old_period_us = pwm_period_us;
 
     // Quick validation - do nothing if the frequency is identical to it's current value.
     if (us == pwm_period_us)
@@ -288,6 +286,7 @@ void pwmout_period_us(pwmout_t *obj, int us)
 
     // Update global frequency timestamps.
     pwm_prescaler = prescaler;
+    pwm_period_us = us;
     pwm_period_ticks = PWM_US_TO_TICKS(us);
 
     pwmout_t pwm;
@@ -296,15 +295,14 @@ void pwmout_period_us(pwmout_t *obj, int us)
 
     // Update all PWM channel values to maintin the same duty cycle (mbed standard behaviour).
     for (int i=0; i<PWM_CHANNELS; i++)
+    {
         if (pwm_ticks[i] != PWM_VALUE_INVALID)
         {
             pwm.pin = pwm_pins[i];
-            pwmout_pulsewidth_us(&pwm, (uint32_t) ((float)pwm_us[i] * ((float)us / (float)pwm_period_us)));
+            pwmout_pulsewidth_us(&pwm, (uint32_t) ((float)pwm_us[i] * ((float)us / (float)old_period_us)));
             pwm.pin = NC;
         }
-
-    // cache our new period in microseconds for later use
-    pwm_period_us = us;
+    }
 }
 
 void pwmout_pulsewidth(pwmout_t *obj, float seconds)