cc2538: pwm: Automatically disable PM1+ if running

The peripheral core clocks of the PWM timers are gated in PM1+, so these
power modes must be disabled if a PWM timer is running. Use
lpm_register_peripheral() to handle this automatically and dynamically.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau.dev@gmail.com>

cpu/cc2538/dev/pwm.c

@@ -46,6 +46,7 @@
 #include "dev/gpio.h"
 #include "dev/sys-ctrl.h"
 #include "dev/pwm.h"
+#include "lpm.h"
 #include <stdio.h>
 #include <stdlib.h>
 /*---------------------------------------------------------------------------*/
@@ -73,6 +74,21 @@ pwm_configured(uint8_t timer, uint8_t ab)
   return 0;
 }
 /*---------------------------------------------------------------------------*/
+static bool
+permit_pm1(void)
+{
+  uint8_t timer, ab;
+
+  for(timer = PWM_TIMER_0; timer <= PWM_TIMER_3; timer++)
+    for(ab = PWM_TIMER_A; ab <= PWM_TIMER_B; ab++)
+      if(pwm_configured(timer, ab) &&
+         REG(PWM_GPTIMER_NUM_TO_BASE(timer) + GPTIMER_CTL) &
+           (ab == PWM_TIMER_A ? GPTIMER_CTL_TAEN : GPTIMER_CTL_TBEN))
+        return false;
+
+  return true;
+}
+/*---------------------------------------------------------------------------*/
 int8_t
 pwm_enable(uint32_t freq, uint8_t duty, uint8_t timer, uint8_t ab)
 {
@@ -95,6 +111,8 @@ pwm_enable(uint32_t freq, uint8_t duty, uint8_t timer, uint8_t ab)
 
   PRINTF("PWM: F%08luHz: %u%% on GPT%u-%u\n", freq, duty, timer, ab);
 
+  lpm_register_peripheral(permit_pm1);
+
   gpt_base = PWM_GPTIMER_NUM_TO_BASE(timer);
   gpt_en = GPTIMER_CTL_TAEN;
   gpt_dir = GPTIMER_CTL_TAPWML;

cpu/cc2538/dev/pwm.h

@@ -47,8 +47,7 @@
  * Depending on the specific needs these limits can be changed to meet a given
  * duty cycle and lower frequencies by using the prescaler (GPTIMER_TnPR).
  *
- * The PWM timer is stopped when dropping below PM0, alternatively you can set
- * LPM_CONF_MAX_PM to zero, or call lpm_max_pm(0)
+ * Running a PWM timer prevents the LPM driver from dropping to PM1+.
  *
  * @{
  *

cpu/cc2538/lpm.c

@@ -101,7 +101,7 @@ static uint8_t max_pm;
 #ifdef LPM_CONF_PERIPH_PERMIT_PM1_FUNCS_MAX
 #define LPM_PERIPH_PERMIT_PM1_FUNCS_MAX LPM_CONF_PERIPH_PERMIT_PM1_FUNCS_MAX
 #else
-#define LPM_PERIPH_PERMIT_PM1_FUNCS_MAX 4
+#define LPM_PERIPH_PERMIT_PM1_FUNCS_MAX 5
 #endif
 
 static lpm_periph_permit_pm1_func_t

examples/zolertia/zoul/test-pwm.c

@@ -35,10 +35,6 @@
  * \defgroup remote-test-pwm Test the CC2538 PWM driver
  *
  * Demonstrates the use of the CC2538 PWM driver for the Zolertia's Zoul boards
- * The PWM timer is stopped when dropping below PM0, alternatively you can set
- * LPM_CONF_MAX_PM to zero, or call lpm_max_pm(0).  In this example is not 
- * needed as we disable RDC in the Makefile, and the CC2538 never drops below
- * PM0
  *
  * @{
  *