stm32: add nucleo-l031k6 support

Adds i2c for all L0 series

UART, Blinky (LED) and i2c tested

14 files changed, 388 insertions, 94 deletions

diff --git a/Makefile b/Makefile
index 6c7f142e3..bcaf50559 100644
--- a/Makefile
+++ b/Makefile
@@ -352,6 +352,8 @@ ifneq ($(STM32), 0)
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=nucleo-f722ze       examples/blinky1
 	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=nucleo-l031k6       examples/blinky1
+	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=nucleo-l432kc       examples/blinky1
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=nucleo-l552ze       examples/blinky1
diff --git a/src/machine/board_lgt92.go b/src/machine/board_lgt92.go
index ee6129b7f..c95de360b 100644
--- a/src/machine/board_lgt92.go
+++ b/src/machine/board_lgt92.go
@@ -41,13 +41,17 @@ const (
 	// LORA RFM95 Radio
 	RFM95_DIO0_PIN = PC13
 
-	//TinyGo UART is MCU LPUSART1
+	// TinyGo UART is MCU LPUSART1
 	UART_RX_PIN = PA13
 	UART_TX_PIN = PA14
 
-	//TinyGo UART1 is MCU USART1
+	// TinyGo UART1 is MCU USART1
 	UART1_RX_PIN = PB6
 	UART1_TX_PIN = PB7
+
+	// MPU9250 Nine-Axis (Gyro + Accelerometer + Compass)
+	I2C0_SCL_PIN = PA9
+	I2C0_SDA_PIN = PA10
 )
 
 var (
@@ -68,6 +72,13 @@ var (
 		RxAltFuncSelector: 0,
 	}
 
+	// MPU9250 Nine-Axis (Gyro + Accelerometer + Compass)
+	I2C1 = &I2C{
+		Bus:             stm32.I2C1,
+		AltFuncSelector: 6,
+	}
+	I2C0 = I2C1
+
 	// SPI
 	SPI0 = SPI{
 		Bus: stm32.SPI1,
diff --git a/src/machine/board_nucleol031k6.go b/src/machine/board_nucleol031k6.go
new file mode 100644
index 000000000..d5fddebf4
--- /dev/null
+++ b/src/machine/board_nucleol031k6.go
@@ -0,0 +1,92 @@
+// +build nucleol031k6
+
+package machine
+
+import (
+	"device/stm32"
+	"runtime/interrupt"
+)
+
+const (
+	LED         = LED_BUILTIN
+	LED_BUILTIN = LED_GREEN
+	LED_GREEN   = PB3
+)
+
+const (
+	// Arduino Pins
+	A0 = PA0 // ADC_IN0
+	A1 = PA1 // ADC_IN1
+	A2 = PA3 // ADC_IN3
+	A3 = PA4 // ADC_IN4
+	A4 = PA5 // ADC_IN5 || I2C1_SDA
+	A5 = PA6 // ADC_IN6 || I2C1_SCL
+	A6 = PA7 // ADC_IN7
+	A7 = PA2 // ADC_IN2
+
+	D0  = PA10 // USART1_TX
+	D1  = PA9  // USART1_RX
+	D2  = PA12
+	D3  = PB0 // TIM2_CH3
+	D4  = PB7
+	D5  = PB6  // TIM16_CH1N
+	D6  = PB1  // TIM14_CH1
+	D9  = PA8  // TIM1_CH1
+	D10 = PA11 // SPI_CS || TIM1_CH4
+	D11 = PB5  // SPI1_MOSI || TIM3_CH2
+	D12 = PB4  // SPI1_MISO
+	D13 = PB3  // SPI1_SCK
+)
+
+const (
+	// UART pins
+	// PA2 and PA15 are connected to the ST-Link Virtual Com Port (VCP)
+	UART_TX_PIN = PA2
+	UART_RX_PIN = PA15
+
+	// SPI
+	SPI1_SCK_PIN = PB3
+	SPI1_SDI_PIN = PB5
+	SPI1_SDO_PIN = PB4
+	SPI0_SCK_PIN = SPI1_SCK_PIN
+	SPI0_SDI_PIN = SPI1_SDI_PIN
+	SPI0_SDO_PIN = SPI1_SDO_PIN
+
+	// I2C pins
+	// PB6 and PB7 are mapped to CN4 pin 7 and CN4 pin 8 respectively with the
+	// default solder bridge settings
+	I2C0_SCL_PIN  = PB7
+	I2C0_SDA_PIN  = PB6
+	I2C0_ALT_FUNC = 1
+)
+
+var (
+	// USART2 is the hardware serial port connected to the onboard ST-LINK
+	// debugger to be exposed as virtual COM port over USB on Nucleo boards.
+	// Both UART0 and UART1 refer to USART2.
+	UART0 = UART{
+		Buffer:            NewRingBuffer(),
+		Bus:               stm32.USART2,
+		TxAltFuncSelector: 4,
+		RxAltFuncSelector: 4,
+	}
+	UART1 = &UART0
+
+	// I2C1 is documented, alias to I2C0 as well
+	I2C1 = &I2C{
+		Bus:             stm32.I2C1,
+		AltFuncSelector: 1,
+	}
+	I2C0 = I2C1
+
+	// SPI
+	SPI0 = SPI{
+		Bus:             stm32.SPI1,
+		AltFuncSelector: 0,
+	}
+	SPI1 = &SPI0
+)
+
+func init() {
+	UART0.Interrupt = interrupt.New(stm32.IRQ_USART2, UART0.handleInterrupt)
+}
diff --git a/src/machine/i2c.go b/src/machine/i2c.go
index 310173614..60204f48d 100644
--- a/src/machine/i2c.go
+++ b/src/machine/i2c.go
@@ -1,4 +1,4 @@
-// +build atmega nrf sam stm32,!stm32l0 fe310 k210
+// +build atmega nrf sam stm32 fe310 k210
 
 package machine
 
diff --git a/src/machine/machine_stm32_i2c_revb.go b/src/machine/machine_stm32_i2c_revb.go
index 63e9205f1..aca962400 100644
--- a/src/machine/machine_stm32_i2c_revb.go
+++ b/src/machine/machine_stm32_i2c_revb.go
@@ -1,4 +1,4 @@
-// +build stm32l5 stm32f7 stm32l4
+// +build stm32l5 stm32f7 stm32l4 stm32l0
 
 package machine
 
diff --git a/src/machine/machine_stm32l0.go b/src/machine/machine_stm32l0.go
index c37d6a027..886c3985a 100644
--- a/src/machine/machine_stm32l0.go
+++ b/src/machine/machine_stm32l0.go
@@ -6,7 +6,6 @@ package machine
 
 import (
 	"device/stm32"
-	"unsafe"
 )
 
 func CPUFrequency() uint32 {
@@ -142,50 +141,6 @@ func (p Pin) enableClock() {
 	}
 }
 
-// Enable peripheral clock
-func enableAltFuncClock(bus unsafe.Pointer) {
-	switch bus {
-	case unsafe.Pointer(stm32.DAC): // DAC interface clock enable
-		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_DACEN)
-	case unsafe.Pointer(stm32.PWR): // Power interface clock enable
-		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_PWREN)
-	case unsafe.Pointer(stm32.I2C3): // I2C3 clock enable
-		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_I2C3EN)
-	case unsafe.Pointer(stm32.I2C2): // I2C2 clock enable
-		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_I2C2EN)
-	case unsafe.Pointer(stm32.I2C1): // I2C1 clock enable
-		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_I2C1EN)
-	case unsafe.Pointer(stm32.USART5): // UART5 clock enable
-		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_USART5EN)
-	case unsafe.Pointer(stm32.USART4): // UART4 clock enable
-		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_USART4EN)
-	case unsafe.Pointer(stm32.USART2): // USART2 clock enable
-		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_USART2EN)
-	case unsafe.Pointer(stm32.SPI2): // SPI2 clock enable
-		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_SPI2EN)
-	case unsafe.Pointer(stm32.LPUART1): // LPUART1 clock enable
-		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_LPUART1EN)
-	case unsafe.Pointer(stm32.WWDG): // Window watchdog clock enable
-		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_WWDGEN)
-	case unsafe.Pointer(stm32.TIM7): // TIM7 clock enable
-		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_TIM7EN)
-	case unsafe.Pointer(stm32.TIM6): // TIM6 clock enable
-		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_TIM6EN)
-	case unsafe.Pointer(stm32.TIM3): // TIM3 clock enable
-		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_TIM3EN)
-	case unsafe.Pointer(stm32.TIM2): // TIM2 clock enable
-		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_TIM2EN)
-	case unsafe.Pointer(stm32.SYSCFG): // System configuration controller clock enable
-		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_SYSCFGEN)
-	case unsafe.Pointer(stm32.SPI1): // SPI1 clock enable
-		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_SPI1EN)
-	case unsafe.Pointer(stm32.ADC): // ADC clock enable
-		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_ADCEN)
-	case unsafe.Pointer(stm32.USART1): // USART1 clock enable
-		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_USART1EN)
-	}
-}
-
 //---------- UART related types and code
 
 // Configure the UART.
@@ -285,3 +240,13 @@ func (spi SPI) configurePins(config SPIConfig) {
 	config.SDO.ConfigureAltFunc(PinConfig{Mode: PinModeSPISDO}, spi.AltFuncSelector)
 	config.SDI.ConfigureAltFunc(PinConfig{Mode: PinModeSPISDI}, spi.AltFuncSelector)
 }
+
+//---------- I2C related types and code
+
+// Gets the value for TIMINGR register
+func (i2c I2C) getFreqRange() uint32 {
+	// This is a 'magic' value calculated by STM32CubeMX
+	// for 80MHz PCLK1.
+	// TODO: Do calculations based on PCLK1
+	return 0x00303D5B
+}
diff --git a/src/machine/machine_stm32l0x1.go b/src/machine/machine_stm32l0x1.go
new file mode 100644
index 000000000..3fad050a6
--- /dev/null
+++ b/src/machine/machine_stm32l0x1.go
@@ -0,0 +1,52 @@
+// +build stm32l0x1
+
+package machine
+
+// Peripheral abstraction layer for the stm32l0
+
+import (
+	"device/stm32"
+	"unsafe"
+)
+
+// Enable peripheral clock
+func enableAltFuncClock(bus unsafe.Pointer) {
+	switch bus {
+	case unsafe.Pointer(stm32.PWR): // Power interface clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_PWREN)
+	case unsafe.Pointer(stm32.I2C3): // I2C3 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_I2C3EN)
+	case unsafe.Pointer(stm32.I2C2): // I2C2 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_I2C2EN)
+	case unsafe.Pointer(stm32.I2C1): // I2C1 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_I2C1EN)
+	case unsafe.Pointer(stm32.USART5): // UART5 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_USART5EN)
+	case unsafe.Pointer(stm32.USART4): // UART4 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_USART4EN)
+	case unsafe.Pointer(stm32.USART2): // USART2 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_USART2EN)
+	case unsafe.Pointer(stm32.SPI2): // SPI2 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_SPI2EN)
+	case unsafe.Pointer(stm32.LPUART1): // LPUART1 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_LPUART1EN)
+	case unsafe.Pointer(stm32.WWDG): // Window watchdog clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_WWDGEN)
+	case unsafe.Pointer(stm32.TIM7): // TIM7 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_TIM7EN)
+	case unsafe.Pointer(stm32.TIM6): // TIM6 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_TIM6EN)
+	case unsafe.Pointer(stm32.TIM3): // TIM3 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_TIM3EN)
+	case unsafe.Pointer(stm32.TIM2): // TIM2 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_TIM2EN)
+	case unsafe.Pointer(stm32.SYSCFG): // System configuration controller clock enable
+		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_SYSCFGEN)
+	case unsafe.Pointer(stm32.SPI1): // SPI1 clock enable
+		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_SPI1EN)
+	case unsafe.Pointer(stm32.ADC): // ADC clock enable
+		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_ADCEN)
+	case unsafe.Pointer(stm32.USART1): // USART1 clock enable
+		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_USART1EN)
+	}
+}
diff --git a/src/machine/machine_stm32l0x2.go b/src/machine/machine_stm32l0x2.go
new file mode 100644
index 000000000..71c7cd4a0
--- /dev/null
+++ b/src/machine/machine_stm32l0x2.go
@@ -0,0 +1,54 @@
+// +build stm32l0x2
+
+package machine
+
+// Peripheral abstraction layer for the stm32l0
+
+import (
+	"device/stm32"
+	"unsafe"
+)
+
+// Enable peripheral clock
+func enableAltFuncClock(bus unsafe.Pointer) {
+	switch bus {
+	case unsafe.Pointer(stm32.DAC): // DAC interface clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_DACEN)
+	case unsafe.Pointer(stm32.PWR): // Power interface clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_PWREN)
+	case unsafe.Pointer(stm32.I2C3): // I2C3 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_I2C3EN)
+	case unsafe.Pointer(stm32.I2C2): // I2C2 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_I2C2EN)
+	case unsafe.Pointer(stm32.I2C1): // I2C1 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_I2C1EN)
+	case unsafe.Pointer(stm32.USART5): // UART5 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_USART5EN)
+	case unsafe.Pointer(stm32.USART4): // UART4 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_USART4EN)
+	case unsafe.Pointer(stm32.USART2): // USART2 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_USART2EN)
+	case unsafe.Pointer(stm32.SPI2): // SPI2 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_SPI2EN)
+	case unsafe.Pointer(stm32.LPUART1): // LPUART1 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_LPUART1EN)
+	case unsafe.Pointer(stm32.WWDG): // Window watchdog clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_WWDGEN)
+	case unsafe.Pointer(stm32.TIM7): // TIM7 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_TIM7EN)
+	case unsafe.Pointer(stm32.TIM6): // TIM6 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_TIM6EN)
+	case unsafe.Pointer(stm32.TIM3): // TIM3 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_TIM3EN)
+	case unsafe.Pointer(stm32.TIM2): // TIM2 clock enable
+		stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_TIM2EN)
+	case unsafe.Pointer(stm32.SYSCFG): // System configuration controller clock enable
+		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_SYSCFGEN)
+	case unsafe.Pointer(stm32.SPI1): // SPI1 clock enable
+		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_SPI1EN)
+	case unsafe.Pointer(stm32.ADC): // ADC clock enable
+		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_ADCEN)
+	case unsafe.Pointer(stm32.USART1): // USART1 clock enable
+		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_USART1EN)
+	}
+}
diff --git a/src/runtime/runtime_stm32l0.go b/src/runtime/runtime_stm32l0.go
index db14a520f..c7045087b 100644
--- a/src/runtime/runtime_stm32l0.go
+++ b/src/runtime/runtime_stm32l0.go
@@ -1,4 +1,4 @@
-// +build stm32,stm32l0
+// +build stm32l0
 
 package runtime
 
@@ -7,68 +7,48 @@ import (
 	"machine"
 )
 
-/*
-   timer settings used for tick and sleep.
-
-   note: TICK_TIMER_FREQ and SLEEP_TIMER_FREQ are controlled by PLL / clock
-   settings above, so must be kept in sync if the clock settings are changed.
-*/
 const (
-	TICK_RATE        = 1000 // 1 KHz
-	TICK_TIMER_IRQ   = stm32.IRQ_TIM7
-	TICK_TIMER_FREQ  = 32000000 // 32 MHz
-	SLEEP_TIMER_IRQ  = stm32.IRQ_TIM3
-	SLEEP_TIMER_FREQ = 32000000 // 32 MHz
+	RCC_SYSCLK_DIV1 = 0 // Needs SVD update (should be stm32.RCC_SYSCLK_DIV1)
 )
 
 type arrtype = uint16
 
-func init() {
-	initCLK()
-
-	initSleepTimer(&timerInfo{
-		EnableRegister: &stm32.RCC.APB1ENR,
-		EnableFlag:     stm32.RCC_APB1ENR_TIM3EN,
-		Device:         stm32.TIM3,
-	})
-
-	machine.UART0.Configure(machine.UARTConfig{})
-
-	initTickTimer(&timerInfo{
-		EnableRegister: &stm32.RCC.APB1ENR,
-		EnableFlag:     stm32.RCC_APB1ENR_TIM7EN,
-		Device:         stm32.TIM7,
-	})
-}
+const asyncScheduler = false
 
 func putchar(c byte) {
 	machine.UART0.WriteByte(c)
 }
 
-// initCLK sets clock to 32MHz
-// SEE: https://github.com/WRansohoff/STM32x0_timer_example/blob/master/src/main.c
-
 func initCLK() {
+	// Set Power Regulator to enable max performance (1.8V)
+	stm32.PWR.CR.ReplaceBits(1<<stm32.PWR_CR_VOS_Pos, stm32.PWR_CR_VOS_Msk, 0)
 
-	// Set the Flash ACR to use 1 wait-state
-	// enable the prefetch buffer and pre-read for performance
-	stm32.FLASH.ACR.SetBits(stm32.Flash_ACR_LATENCY | stm32.Flash_ACR_PRFTEN | stm32.Flash_ACR_PRE_READ)
-
-	// Set presaclers so half system clock (PCLKx = HCLK/2)
-	stm32.RCC.CFGR.SetBits(stm32.RCC_CFGR_PPRE1_Div2 << stm32.RCC_CFGR_PPRE1_Pos)
-	stm32.RCC.CFGR.SetBits(stm32.RCC_CFGR_PPRE2_Div2 << stm32.RCC_CFGR_PPRE2_Pos)
+	// Calibration (default 0x10)
+	stm32.RCC.ICSCR.ReplaceBits(0x10<<stm32.RCC_ICSCR_HSI16TRIM_Pos, stm32.RCC_ICSCR_HSI16TRIM_Msk, 0)
 
 	// Enable the HSI16 oscillator, since the L0 series boots to the MSI one.
-	stm32.RCC.CR.SetBits(stm32.RCC_CR_HSI16ON)
+	stm32.RCC.CR.ReplaceBits(stm32.RCC_CR_HSI16ON, stm32.RCC_CR_HSI16ON_Msk|stm32.RCC_CR_HSI16DIVEN_Msk, 0)
 
 	// Wait for HSI16 to be ready
 	for !stm32.RCC.CR.HasBits(stm32.RCC_CR_HSI16RDYF) {
 	}
 
+	// Disable PLL
+	stm32.RCC.CR.ClearBits(stm32.RCC_CR_PLLON)
+
+	// Wait for PLL to be disabled
+	for stm32.RCC.CR.HasBits(stm32.RCC_CR_PLLRDY) {
+	}
+
 	// Configure the PLL to use HSI16 with a PLLDIV of 2 and PLLMUL of 4.
-	stm32.RCC.CFGR.SetBits(0x01<<stm32.RCC_CFGR_PLLDIV_Pos | 0x01<<stm32.RCC_CFGR_PLLMUL_Pos)
-	stm32.RCC.CFGR.ClearBits(0x02<<stm32.RCC_CFGR_PLLDIV_Pos | 0x0E<<stm32.RCC_CFGR_PLLMUL_Pos)
-	stm32.RCC.CFGR.ClearBits(stm32.RCC_CFGR_PLLSRC)
+	stm32.RCC.CFGR.ReplaceBits(
+		(stm32.RCC_CFGR_PLLSRC_HSI16<<stm32.RCC_CFGR_PLLSRC_Pos)|
+			(stm32.RCC_CFGR_PLLMUL_Mul4<<stm32.RCC_CFGR_PLLMUL_Pos)|
+			(stm32.RCC_CFGR_PLLDIV_Div2<<stm32.RCC_CFGR_PLLDIV_Pos),
+		stm32.RCC_CFGR_PLLSRC_Msk|
+			stm32.RCC_CFGR_PLLMUL_Msk|
+			stm32.RCC_CFGR_PLLDIV_Msk,
+		0)
 
 	// Enable PLL
 	stm32.RCC.CR.SetBits(stm32.RCC_CR_PLLON)
@@ -77,9 +57,30 @@ func initCLK() {
 	for !stm32.RCC.CR.HasBits(stm32.RCC_CR_PLLRDY) {
 	}
 
+	// Adjust flash latency
+	if FlashLatency > getFlashLatency() {
+		setFlashLatency(FlashLatency)
+		for getFlashLatency() != FlashLatency {
+		}
+	}
+
+	// HCLK
+	stm32.RCC.CFGR.ReplaceBits(RCC_SYSCLK_DIV1, stm32.RCC_CFGR_HPRE_Msk, 0)
+
 	// Use PLL As System clock
-	stm32.RCC.CFGR.SetBits(0x3)
+	stm32.RCC.CFGR.ReplaceBits(stm32.RCC_CFGR_SWS_PLL, stm32.RCC_CFGR_SW_Msk, 0)
+	for stm32.RCC.CFGR.Get()&stm32.RCC_CFGR_SW_Msk != stm32.RCC_CFGR_SWS_PLL {
+	}
 
+	// Set prescalers so half system clock (PCLKx = HCLK/2)
+	stm32.RCC.CFGR.SetBits(stm32.RCC_CFGR_PPRE1_Div2 << stm32.RCC_CFGR_PPRE1_Pos)
+	stm32.RCC.CFGR.SetBits(stm32.RCC_CFGR_PPRE2_Div2 << stm32.RCC_CFGR_PPRE2_Pos)
 }
 
-const asyncScheduler = false
+func getFlashLatency() uint32 {
+	return stm32.FLASH.ACR.Get() & stm32.Flash_ACR_LATENCY_Msk
+}
+
+func setFlashLatency(l uint32) {
+	stm32.FLASH.ACR.ReplaceBits(l, stm32.Flash_ACR_LATENCY_Msk, 0)
+}
diff --git a/src/runtime/runtime_stm32l0x1.go b/src/runtime/runtime_stm32l0x1.go
new file mode 100644
index 000000000..1d48388e8
--- /dev/null
+++ b/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,
+	})
+}
diff --git a/src/runtime/runtime_stm32l0x2.go b/src/runtime/runtime_stm32l0x2.go
new file mode 100644
index 000000000..6eccf0eb6
--- /dev/null
+++ b/src/runtime/runtime_stm32l0x2.go
@@ -0,0 +1,44 @@
+// +build stm32l0x2
+
+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_TIM7
+	TICK_TIMER_FREQ  = 32000000 // 32 MHz
+	SLEEP_TIMER_IRQ  = stm32.IRQ_TIM3
+	SLEEP_TIMER_FREQ = 32000000 // 32 MHz
+)
+
+const (
+	FlashLatency = stm32.Flash_ACR_LATENCY_WS1
+)
+
+func init() {
+	initCLK()
+
+	initSleepTimer(&timerInfo{
+		EnableRegister: &stm32.RCC.APB1ENR,
+		EnableFlag:     stm32.RCC_APB1ENR_TIM3EN,
+		Device:         stm32.TIM3,
+	})
+
+	machine.UART0.Configure(machine.UARTConfig{})
+
+	initTickTimer(&timerInfo{
+		EnableRegister: &stm32.RCC.APB1ENR,
+		EnableFlag:     stm32.RCC_APB1ENR_TIM7EN,
+		Device:         stm32.TIM7,
+	})
+}
diff --git a/targets/cortex-m0.json b/targets/cortex-m0.json
new file mode 100644
index 000000000..8cbbe2850
--- /dev/null
+++ b/targets/cortex-m0.json
@@ -0,0 +1,8 @@
+{
+	"inherits": ["cortex-m"],
+	"llvm-target": "armv6m-none-eabi",
+	"cflags": [
+		"--target=armv6m-none-eabi",
+		"-Qunused-arguments"
+	]
+}
diff --git a/targets/nucleo-l031k6.json b/targets/nucleo-l031k6.json
new file mode 100644
index 000000000..928dd43dc
--- /dev/null
+++ b/targets/nucleo-l031k6.json
@@ -0,0 +1,11 @@
+{
+    "inherits": ["cortex-m0"],
+    "build-tags": ["nucleol031k6", "stm32l031", "stm32l0x1", "stm32l0", "stm32"],
+    "linkerscript": "targets/stm32l031k6.ld",
+    "extra-files": [
+        "src/device/stm32/stm32l0x1.s"
+    ],
+    "flash-method": "openocd",
+    "openocd-interface": "stlink",
+    "openocd-target": "stm32l0"
+}
\ No newline at end of file
diff --git a/targets/stm32l031k6.ld b/targets/stm32l031k6.ld
new file mode 100644
index 000000000..f9995bc02
--- /dev/null
+++ b/targets/stm32l031k6.ld
@@ -0,0 +1,10 @@
+
+MEMORY
+{
+  FLASH_TEXT (rx) : ORIGIN = 0x08000000, LENGTH = 32K
+  RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 8K
+}
+
+_stack_size = 2K;
+
+INCLUDE "targets/arm.ld"
\ No newline at end of file