boards/*efm32*: do not force RTT_FREQUENCY

while keeping a sane (rtt shared with rtc (counter)) default
this commit adds the ability to define RTT_FREQUENCY
to some thing different than 1 Hz

boards/common/slwstk6000b/include/periph_conf.h

@@ -106,8 +106,9 @@ static const i2c_conf_t i2c_config[] = {
  * @name    RTT configuration
  * @{
  */
-#define RTT_MAX_VALUE       (0xFFFFFFFF)
-#define RTT_FREQUENCY       (1U)
+#ifndef RTT_FREQUENCY
+#define RTT_FREQUENCY       (1U)              /* in Hz */
+#endif
 /** @} */
 
 /**

boards/e180-zg120b-tb/include/periph_conf.h

@@ -84,8 +84,9 @@ static const adc_chan_conf_t adc_channel_config[] = {
  * @name    RTT configuration
  * @{
  */
-#define RTT_MAX_VALUE       (0xFFFFFFFF)
-#define RTT_FREQUENCY       (1U)
+#ifndef RTT_FREQUENCY
+#define RTT_FREQUENCY       (1U)              /* in Hz */
+#endif
 /** @} */
 
 /**

boards/ikea-tradfri/include/periph_conf.h

@@ -82,8 +82,9 @@ static const adc_chan_conf_t adc_channel_config[] = {
  * @name    RTT configuration
  * @{
  */
-#define RTT_MAX_VALUE       (0xFFFFFFFF)
-#define RTT_FREQUENCY       (1U)
+#ifndef RTT_FREQUENCY
+#define RTT_FREQUENCY       (1U)              /* in Hz */
+#endif
 /** @} */
 
 /**

boards/slstk3400a/include/periph_conf.h

@@ -101,8 +101,9 @@ static const i2c_conf_t i2c_config[] = {
  * @name    RTT configuration
  * @{
  */
-#define RTT_MAX_VALUE       (0xFFFFFF)
-#define RTT_FREQUENCY       (1U)
+#ifndef RTT_FREQUENCY
+#define RTT_FREQUENCY       (1U)              /* in Hz */
+#endif
 /** @} */
 
 /**

boards/slstk3401a/include/periph_conf.h

@@ -113,8 +113,9 @@ static const i2c_conf_t i2c_config[] = {
  * @name    RTT configuration
  * @{
  */
-#define RTT_MAX_VALUE       (0xFFFFFFFF)
-#define RTT_FREQUENCY       (1U)
+#ifndef RTT_FREQUENCY
+#define RTT_FREQUENCY       (1U)              /* in Hz */
+#endif
 /** @} */
 
 /**

boards/slstk3402a/include/periph_conf.h

@@ -104,8 +104,9 @@ static const i2c_conf_t i2c_config[] = {
  * @name    RTT configuration
  * @{
  */
-#define RTT_MAX_VALUE       (0xFFFFFFFF)
-#define RTT_FREQUENCY       (1U)
+#ifndef RTT_FREQUENCY
+#define RTT_FREQUENCY       (1U)              /* in Hz */
+#endif
 /** @} */
 
 /**

boards/sltb001a/include/periph_conf.h

@@ -113,8 +113,9 @@ static const i2c_conf_t i2c_config[] = {
  * @name    RTT configuration
  * @{
  */
-#define RTT_MAX_VALUE       (0xFFFFFFFF)
-#define RTT_FREQUENCY       (1U)
+#ifndef RTT_FREQUENCY
+#define RTT_FREQUENCY       (1U)              /* in Hz */
+#endif
 /** @} */
 
 /**

boards/slwstk6220a/include/periph_conf.h

@@ -154,8 +154,9 @@ static const pwm_conf_t pwm_config[] = {
  * @name    RTT configuration
  * @{
  */
-#define RTT_MAX_VALUE       (0xFFFFFF)
-#define RTT_FREQUENCY       (1U)
+#ifndef RTT_FREQUENCY
+#define RTT_FREQUENCY       (1U)              /* in Hz */
+#endif
 /** @} */
 
 /**

boards/stk3200/include/periph_conf.h

@@ -100,8 +100,9 @@ static const i2c_conf_t i2c_config[] = {
  * @name    RTT configuration
  * @{
  */
-#define RTT_MAX_VALUE       (0xFFFFFF)
-#define RTT_FREQUENCY       (1U)
+#ifndef RTT_FREQUENCY
+#define RTT_FREQUENCY       (1U)              /* in Hz */
+#endif
 /** @} */
 
 /**

boards/stk3600/include/periph_conf.h

@@ -159,8 +159,9 @@ static const pwm_conf_t pwm_config[] = {
  * @name    RTT configuration
  * @{
  */
-#define RTT_MAX_VALUE       (0xFFFFFF)
-#define RTT_FREQUENCY       (1U)
+#ifndef RTT_FREQUENCY
+#define RTT_FREQUENCY       (1U)              /* in Hz */
+#endif
 /** @} */
 
 /**

boards/stk3700/include/periph_conf.h

@@ -159,8 +159,9 @@ static const pwm_conf_t pwm_config[] = {
  * @name    RTT configuration
  * @{
  */
-#define RTT_MAX_VALUE       (0xFFFFFF)
-#define RTT_FREQUENCY       (1U)
+#ifndef RTT_FREQUENCY
+#define RTT_FREQUENCY       (1U)              /* in Hz */
+#endif
 /** @} */
 
 /**