stm32/i2c: Add hardware I2C implementation for STM32L4.

For STM32L4, hardware I2C can be implemented by using TIMINGR.
This commit enables:
- Use of hardware I2C in machine.I2C.
- Specifying a frequency greater than or equal to 400KHz with pyb.I2C.

ports/stm32/i2c.c

@@ -269,11 +269,18 @@ int i2c_write(i2c_t *i2c, const uint8_t *src, size_t len, size_t next_len) {
     return num_acks;
 }
 
-#elif defined(STM32F0) || defined(STM32F7) || defined(STM32H7)
+#elif defined(STM32F0) || defined(STM32F7) || defined(STM32H7) || defined(STM32L4)
 
 #if defined(STM32H7)
 #define APB1ENR            APB1LENR
 #define RCC_APB1ENR_I2C1EN RCC_APB1LENR_I2C1EN
+#elif defined(STM32L4)
+#define APB1ENR            APB1ENR1
+#define RCC_APB1ENR_I2C1EN RCC_APB1ENR1_I2C1EN
+#if defined(STM32L432xx)
+// Not a real peripheral, only needed for i2c_id calculation in i2c_init.
+#define I2C2_BASE          (APB1PERIPH_BASE + 0x5800UL)
+#endif
 #endif
 
 STATIC uint16_t i2c_timeout_ms[MICROPY_HW_MAX_I2C];
@@ -303,6 +310,18 @@ int i2c_init(i2c_t *i2c, mp_hal_pin_obj_t scl, mp_hal_pin_obj_t sda, uint32_t fr
     i2c->OAR1 = 0;
     i2c->OAR2 = 0;
 
+    #if defined(STM32L4)
+    // These timing values are with f_I2CCLK=80MHz and are only approximate
+    if (freq >= 1000000) {
+        i2c->TIMINGR = 0x00300F33;
+    } else if (freq >= 400000) {
+        i2c->TIMINGR = 0x00702991;
+    } else if (freq >= 100000) {
+        i2c->TIMINGR = 0x10909CEC;
+    } else {
+        return -MP_EINVAL;
+    }
+    #else
     // These timing values are for f_I2CCLK=54MHz and are only approximate
     if (freq >= 1000000) {
         i2c->TIMINGR = 0x50100103;
@@ -313,6 +332,7 @@ int i2c_init(i2c_t *i2c, mp_hal_pin_obj_t scl, mp_hal_pin_obj_t sda, uint32_t fr
     } else {
         return -MP_EINVAL;
     }
+    #endif
 
     i2c->TIMEOUTR = 0;
 

ports/stm32/machine_i2c.c

@@ -38,7 +38,7 @@
 
 #define I2C_POLL_DEFAULT_TIMEOUT_US (50000) // 50ms
 
-#if defined(STM32F0) || defined(STM32F4) || defined(STM32F7) || defined(STM32H7) || defined(STM32L1)
+#if defined(STM32F0) || defined(STM32F4) || defined(STM32F7) || defined(STM32H7) || defined(STM32L1) || defined(STM32L4)
 
 typedef struct _machine_hard_i2c_obj_t {
     mp_obj_base_t base;
@@ -186,7 +186,7 @@ STATIC void machine_hard_i2c_init(machine_hard_i2c_obj_t *self, uint32_t freq, u
 /******************************************************************************/
 /* MicroPython bindings for machine API                                       */
 
-#if defined(STM32F0) || defined(STM32F7) || defined(STM32H7)
+#if defined(STM32F0) || defined(STM32F7) || defined(STM32H7) || defined(STM32L4)
 #define MACHINE_I2C_TIMINGR (1)
 #else
 #define MACHINE_I2C_TIMINGR (0)

ports/stm32/pyb_i2c.c

@@ -208,11 +208,14 @@ const pyb_i2c_obj_t pyb_i2c_obj[] = {
 
 #elif defined(STM32L4)
 
-// The value 0x90112626 was obtained from the DISCOVERY_I2C1_TIMING constant
-// defined in the STM32L4Cube file Drivers/BSP/STM32L476G-Discovery/stm32l476g_discovery.h
-#define MICROPY_HW_I2C_BAUDRATE_TIMING {{PYB_I2C_SPEED_STANDARD, 0x90112626}}
-#define MICROPY_HW_I2C_BAUDRATE_DEFAULT (PYB_I2C_SPEED_STANDARD)
-#define MICROPY_HW_I2C_BAUDRATE_MAX (PYB_I2C_SPEED_STANDARD)
+// generated using CubeMX
+#define MICROPY_HW_I2C_BAUDRATE_TIMING { \
+        {PYB_I2C_SPEED_STANDARD, 0x10909CEC}, \
+        {PYB_I2C_SPEED_FULL, 0x00702991}, \
+        {PYB_I2C_SPEED_FAST, 0x00300F33}, \
+}
+#define MICROPY_HW_I2C_BAUDRATE_DEFAULT (PYB_I2C_SPEED_FULL)
+#define MICROPY_HW_I2C_BAUDRATE_MAX (PYB_I2C_SPEED_FAST)
 
 #else
 #error "no I2C timings for this MCU"