stm32: add nucleo-l031k6 support

Adds i2c for all L0 series

UART, Blinky (LED) and i2c tested

src/runtime/runtime_stm32l0x1.go

@@ -0,0 +1,44 @@
+// +build stm32l0x1
+
+package runtime
+
+import (
+	"device/stm32"
+	"machine"
+)
+
+/*
+   timer settings used for tick and sleep.
+
+   note: TICK_TIMER_FREQ and SLEEP_TIMER_FREQ are controlled by PLL / clock
+   settings, so must be kept in sync if the clock settings are changed.
+*/
+const (
+	TICK_RATE        = 1000 // 1 KHz
+	TICK_TIMER_IRQ   = stm32.IRQ_TIM21
+	TICK_TIMER_FREQ  = 32000000 // 32 MHz
+	SLEEP_TIMER_IRQ  = stm32.IRQ_TIM22
+	SLEEP_TIMER_FREQ = 32000000 // 32 MHz
+)
+
+const (
+	FlashLatency = stm32.Flash_ACR_LATENCY_WS1
+)
+
+func init() {
+	initCLK()
+
+	initSleepTimer(&timerInfo{
+		EnableRegister: &stm32.RCC.APB2ENR,
+		EnableFlag:     stm32.RCC_APB2ENR_TIM22EN,
+		Device:         stm32.TIM22,
+	})
+
+	machine.UART0.Configure(machine.UARTConfig{})
+
+	initTickTimer(&timerInfo{
+		EnableRegister: &stm32.RCC.APB2ENR,
+		EnableFlag:     stm32.RCC_APB2ENR_TIM21EN,
+		Device:         stm32.TIM21,
+	})
+}