diff --git a/tmk_core/common/chibios/sleep_led.c b/tmk_core/common/chibios/sleep_led.c
index fad7ac04..d9cdeba1 100644
--- a/tmk_core/common/chibios/sleep_led.c
+++ b/tmk_core/common/chibios/sleep_led.c
@@ -1,23 +1,152 @@
 #include "ch.h"
+#include "hal.h"
 
 #include "led.h"
 #include "sleep_led.h"
 
+#if defined(KL2x) || defined(K20x) /* platform selection: familiar Kinetis chips */
+/* All right, we go the "software" way: LP timer, toggle LED in interrupt.
+ * Based on hasu's code for AVRs.
+ */
+
+/* Breathing Sleep LED brighness(PWM On period) table
+ * (64[steps] * 4[duration]) / 64[PWM periods/s] = 4 second breath cycle
+ *
+ * http://www.wolframalpha.com/input/?i=%28sin%28+x%2F64*pi%29**8+*+255%2C+x%3D0+to+63
+ * (0..63).each {|x| p ((sin(x/64.0*PI)**8)*255).to_i }
+ */
+static const uint8_t breathing_table[64] = {
+0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 4, 6, 10,
+15, 23, 32, 44, 58, 74, 93, 113, 135, 157, 179, 199, 218, 233, 245, 252,
+255, 252, 245, 233, 218, 199, 179, 157, 135, 113, 93, 74, 58, 44, 32, 23,
+15, 10, 6, 4, 2, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
+};
+
+/* LP Timer interrupt handler */
+OSAL_IRQ_HANDLER(KINETIS_LPTMR0_IRQ_VECTOR) {
+    OSAL_IRQ_PROLOGUE();
+
+    /* Software PWM
+    * timer:1111 1111 1111 1111
+    *       \_____/\/ \_______/____  count(0-255)
+    *          \    \______________  duration of step(4)
+    *           \__________________  index of step table(0-63)
+    */
+
+    // this works for cca 65536 irqs/sec
+    static union {
+    uint16_t row;
+    struct {
+      uint8_t count:8;
+      uint8_t duration:2;
+      uint8_t index:6;
+    } pwm;
+    } timer = { .row = 0 };
+
+    timer.row++;
+
+    // LED on
+    if (timer.pwm.count == 0) {
+        led_set(1<<USB_LED_CAPS_LOCK);
+    }
+    // LED off
+    if (timer.pwm.count == breathing_table[timer.pwm.index]) {
+        led_set(0);
+    }
+
+    /* Reset the counter */
+    LPTMR0->CSR |= LPTMRx_CSR_TCF;
+
+    OSAL_IRQ_EPILOGUE();
+}
+
+/* LPTMR clock options */
+#define LPTMR_CLOCK_MCGIRCLK 0 /* 4MHz clock */
+#define LPTMR_CLOCK_LPO      1 /* 1kHz clock */
+#define LPTMR_CLOCK_ERCLK32K 2
+#define LPTMR_CLOCK_OSCERCLK 3 /* output from OSC */
+
+/* Work around inconsistencies in Freescale naming */
+#if !defined(SIM_SCGC5_LPTMR)
+#define SIM_SCGC5_LPTMR SIM_SCGC5_LPTIMER
+#endif
+
+/* Initialise the timer */
 void sleep_led_init(void) {
-	// we could go the 'software way' -- just enable *some* timer
-	// and go with callbacks
-	// or we could go the 'hardware way' -- and use timer output to
-	// pins directly
+    /* Make sure the clock to the LPTMR is enabled */
+    SIM->SCGC5 |= SIM_SCGC5_LPTMR;
+    /* Reset LPTMR settings */
+    LPTMR0->CSR = 0;
+    /* Set the compare value */
+    LPTMR0->CMR = 1;  // trigger on counter value (i.e. every time)
+    /* Set up clock source and prescaler */
+    /* Software PWM
+    *  ______           ______           __
+    * |  ON  |___OFF___|  ON  |___OFF___|   ....
+    * |<-------------->|<-------------->|<- ....
+    *     PWM period       PWM period
+    *
+    * R                interrupts/period[resolution]
+    * F                periods/second[frequency]
+    * R * F            interrupts/second
+    */
+    /* === OPTION 1 === */
+    //  for 1kHz LPO
+    //  No prescaler => 1024 irqs/sec
+    // LPTMR0->PSR = LPTMRx_PSR_PCS(LPTMR_CLOCK_LPO)|LPTMRx_PSR_PBYP;
+    /* === OPTION 2 === */
+    //  for nMHz IRC (n=4 on KL25Z, KL26Z and K20x; n=2 or 8 on KL27Z)
+    MCG->C2 |= MCG_C2_IRCS; // fast (4MHz) internal ref clock
+    #if defined(KL27Z) // divide the 8MHz IRC by 2, to have the same MCGIRCLK speed as others
+    MCG->MC |= MCG_MC_LIRC_DIV2_DIV2;
+    #endif /* KL27Z */
+    MCG->C1 |= MCG_C1_IRCLKEN; // enable internal ref clock
+    //  to work in stop mode, also MCG_C1_IREFSTEN
+    //  Divide 4MHz by 2^N (N=5) => 62500 irqs/sec =>
+    //  => approx F=61, R=256, duration = 4
+    LPTMR0->PSR = LPTMRx_PSR_PCS(LPTMR_CLOCK_MCGIRCLK)|LPTMRx_PSR_PRESCALE(5);
+    /* === OPTION 3 === */
+    //  for OSC output (external crystal), usually 8MHz or 16MHz
+    // OSC0->CR |= OSC_CR_ERCLKEN; // enable ext ref clock
+    //  to work in stop mode, also OSC_CR_EREFSTEN
+    //  Divide by 2^N
+    // LPTMR0->PSR = LPTMRx_PSR_PCS(LPTMR_CLOCK_OSCERCLK)|LPTMRx_PSR_PRESCALE(7);
+    /* === END OPTIONS === */
+    /* Interrupt on TCF set (compare flag) */
+    nvicEnableVector(LPTMR0_IRQn, 2); // vector, priority
+    LPTMR0->CSR |= LPTMRx_CSR_TIE;
 }
 
 void sleep_led_enable(void) {
-    led_set(1<<USB_LED_CAPS_LOCK);
+    /* Enable the timer */
+    LPTMR0->CSR |= LPTMRx_CSR_TEN;
 }
 
 void sleep_led_disable(void) {
-    led_set(0);
+    /* Disable the timer */
+    LPTMR0->CSR &= ~LPTMRx_CSR_TEN;
 }
 
 void sleep_led_toggle(void) {
-    // not working yet, state not saved anywhere currently
+    /* Toggle the timer */
+    LPTMR0->CSR ^= LPTMRx_CSR_TEN;
 }
+
+#else /* platform selection: not on familiar Kinetis chips */
+
+void sleep_led_init(void) {
+}
+ 
+void sleep_led_enable(void) {
+    led_set(1<<USB_LED_CAPS_LOCK);
+}
+ 
+void sleep_led_disable(void) {
+    led_set(0);
+}
+ 
+void sleep_led_toggle(void) {
+    // not implemented
+}
+
+#endif /* platform selection */
\ No newline at end of file