feather-stm32f405: add I2C support (#1378)

* machine/stm32f405: add initial I2C support

Author: ardnew

src/machine/board_feather-stm32f405.go

@@ -202,11 +202,11 @@ const (
 	// #===========#==========#==============#==============#=======#=======#
 	// | Interface | Hardware |  Bus(Freq)   | SDA/SCL Pins | AltFn | Alias |
 	// #===========#==========#==============#==============#=======#=======#
-	// |   I2C1    |   I2C1   |              |   D14/D15    |       |   ~   |
-	// |   I2C2    |   I2C2   |              |    D0/D1     |       |   ~   |
-	// |   I2C3    |   I2C1   |              |    D9/D10    |       |   ~   |
+	// |   I2C1    |   I2C1   | APB1(42 MHz) |   D14/D15    |   4   |   ~   |
+	// |   I2C2    |   I2C2   | APB1(42 MHz) |    D0/D1     |   4   |   ~   |
+	// |   I2C3    |   I2C1   | APB1(42 MHz) |    D9/D10    |   4   |   ~   |
 	// | --------- | -------- | ------------ | ------------ | ----- | ----- |
-	// |   I2C0    |   I2C1   |              |   D14/D15    |       | I2C1  |
+	// |   I2C0    |   I2C1   | APB1(42 MHz) |   D14/D15    |   4   | I2C1  |
 	// #===========#==========#==============#==============#=======#=======#
 	NUM_I2C_INTERFACES = 3
 
@@ -226,4 +226,20 @@ const (
 	I2C_SCL_PIN = I2C0_SCL_PIN //
 )
 
+var (
+	I2C1 = I2C{
+		Bus:             stm32.I2C1,
+		AltFuncSelector: stm32.AF4_I2C1_2_3,
+	}
+	I2C2 = I2C{
+		Bus:             stm32.I2C2,
+		AltFuncSelector: stm32.AF4_I2C1_2_3,
+	}
+	I2C3 = I2C{
+		Bus:             stm32.I2C1,
+		AltFuncSelector: stm32.AF4_I2C1_2_3,
+	}
+	I2C0 = I2C1
+)
+
 func initI2C() {}

src/machine/i2c.go

@@ -1,4 +1,4 @@
-// +build avr nrf sam stm32,!stm32f4 fe310 k210
+// +build avr nrf sam stm32,!stm32f407 fe310 k210
 
 package machine