kinetis: fix warnings

- find_closest_x: sign-compare
 - hwtimer_arch: unused-parameter
 - i2c_init_slave: unused-parameter
 - rnga: sign-compare
 - rngb: sign-compare
 - spi_transfer_bytes: sign-compare
 - spi_transfer_regs: sign-compare
 - timer: unused-parameter

cpu/kinetis_common/hwtimer_arch.c

@@ -87,6 +87,7 @@ inline static void hwtimer_stop(void)
 
 void hwtimer_arch_init(void (*handler)(int), uint32_t fcpu)
 {
+    (void) fcpu; /* fcpu does not affect the Low power timer module frequency */
     timeout_handler = handler;
 
     /* unlock LPTIMER_DEV */
@@ -146,7 +147,7 @@ void hwtimer_arch_disable_interrupt(void)
 
 void hwtimer_arch_set(unsigned long offset, short timer)
 {
-    (void)timer;
+    (void)timer; /* we only support one timer */
     stimer.counter32b += lptmr_get_cnr();
     hwtimer_stop();
 
@@ -165,7 +166,7 @@ void hwtimer_arch_set(unsigned long offset, short timer)
 
 void hwtimer_arch_set_absolute(unsigned long value, short timer)
 {
-    (void)timer;
+    (void)timer; /* we only support one timer */
     stimer.counter32b += lptmr_get_cnr();
     hwtimer_stop();
 
@@ -184,6 +185,7 @@ void hwtimer_arch_set_absolute(unsigned long value, short timer)
 
 void hwtimer_arch_unset(short timer)
 {
+    (void)timer; /* we only support one timer */
     stimer.counter32b += lptmr_get_cnr();
     hwtimer_stop();
     stimer.diff = 0;

cpu/kinetis_common/i2c.c

@@ -155,6 +155,8 @@ int i2c_init_master(i2c_t dev, i2c_speed_t speed)
 int i2c_init_slave(i2c_t dev, uint8_t address)
 {
     /* TODO: implement slave mode */
+    (void) dev;
+    (void) address;
     return -1;
 }
 

cpu/kinetis_common/random_rnga.c

@@ -35,7 +35,7 @@ void random_init(void)
 
 int random_read(char *buf, unsigned int num)
 {
-    int count = 0;
+    unsigned int count = 0;
 
     /* self-seeding */
     while (!(KINETIS_RNGA->SR & RNG_SR_OREG_LVL_MASK));
@@ -55,7 +55,7 @@ int random_read(char *buf, unsigned int num)
         }
     }
 
-    return count;
+    return (int)count;
 }
 
 void random_poweron(void)

cpu/kinetis_common/random_rngb.c

@@ -37,7 +37,7 @@ void random_init(void)
 
 int random_read(char *buf, unsigned int num)
 {
-    int count = 0;
+    unsigned int count = 0;
 
     while (count < num) {
         uint32_t tmp;
@@ -54,7 +54,7 @@ int random_read(char *buf, unsigned int num)
         }
     }
 
-    return count;
+    return (int)count;
 }
 
 void random_poweron(void)

cpu/kinetis_common/spi.c

@@ -464,12 +464,12 @@ static spi_state_t spi_config[SPI_NUMOF];
  * @return The actual achieved frequency on success
  * @return Less than 0 on error.
  */
-static int find_closest_baudrate_scalers(const uint32_t module_clock, const uint32_t target_clock,
+static long find_closest_baudrate_scalers(const uint32_t module_clock, const long target_clock,
         uint8_t *closest_prescaler, uint8_t *closest_scaler)
 {
     uint8_t i;
     uint8_t k;
-    int freq;
+    long freq;
     static const uint8_t num_scalers = 16;
     static const uint8_t num_prescalers = 4;
     static const int br_scalers[16] = {
@@ -478,7 +478,7 @@ static int find_closest_baudrate_scalers(const uint32_t module_clock, const uint
     };
     static const int br_prescalers[4] = {2, 3, 5, 7};
 
-    int closest_frequency = -1;
+    long closest_frequency = -1;
 
     /* Test all combinations until we arrive close to the target clock */
     for (i = 0; i < num_prescalers; ++i) {
@@ -533,18 +533,18 @@ static int find_closest_baudrate_scalers(const uint32_t module_clock, const uint
  * @return The actual achieved frequency on success
  * @return Less than 0 on error.
  */
-static int find_closest_delay_scalers(const uint32_t module_clock, const uint32_t target_freq,
+static long find_closest_delay_scalers(const uint32_t module_clock, const long target_freq,
                                       uint8_t *closest_prescaler, uint8_t *closest_scaler)
 {
     uint8_t i;
     uint8_t k;
-    int freq;
+    long freq;
     int prescaler;
     int scaler;
     static const uint8_t num_scalers = 16;
     static const uint8_t num_prescalers = 4;
 
-    int closest_frequency = -1;
+    long closest_frequency = -1;
 
     /* Test all combinations until we arrive close to the target clock */
     for (i = 0; i < num_prescalers; ++i) {
@@ -1041,13 +1041,13 @@ int spi_transfer_bytes(spi_t dev, char *out, char *in, unsigned int length)
     /* Default: send idle data */
     byte_out = (uint8_t)SPI_IDLE_DATA;
 
-    for (i = 0; i < length; i++) {
+    for (i = 0; i < (int)length; i++) {
         if (out != NULL) {
             /* Send given out data */
             byte_out = (uint8_t)out[i];
         }
 
-        if (i >= length - 1) {
+        if (i >= (int)length - 1) {
             /* Last byte, set End-of-Queue flag, clear Continue flag. */
             flags &= ~(SPI_PUSHR_CONT_MASK);
             flags |= SPI_PUSHR_EOQ_MASK;
@@ -1248,13 +1248,13 @@ int spi_transfer_regs(spi_t dev, uint8_t reg, char *out, char *in, unsigned int
     /* Default: send idle data */
     byte_out = (uint8_t)SPI_IDLE_DATA;
 
-    for (i = 0; i < length; i++) {
+    for (i = 0; i < (int)length; i++) {
         if (out != NULL) {
             /* Send given out data */
             byte_out = (uint8_t)out[i];
         }
 
-        if (i >= length - 1) {
+        if (i >= (int)length - 1) {
             /* Last byte, set End-of-Queue flag, clear Continue flag. */
             flags &= ~(SPI_PUSHR_CONT_MASK);
             flags |= SPI_PUSHR_EOQ_MASK;

cpu/kinetis_common/timer.c

@@ -144,6 +144,7 @@ int timer_set(tim_t dev, int channel, unsigned int timeout)
 
 int timer_set_absolute(tim_t dev, int channel, unsigned int value)
 {
+    (void) channel; /* we only support one channel */
     switch (dev) {
 #if TIMER_0_EN
 
@@ -179,6 +180,7 @@ int timer_set_absolute(tim_t dev, int channel, unsigned int value)
 
 int timer_clear(tim_t dev, int channel)
 {
+    (void) channel; /* we only support one channel */
     switch (dev) {
 #if TIMER_0_EN