add optional secondary I2C singleton

Author: Neradoc

py/circuitpy_mpconfig.h

@@ -253,6 +253,7 @@ typedef long mp_off_t;
 
 #if CIRCUITPY_BOARD
 #define BOARD_I2C (defined(DEFAULT_I2C_BUS_SDA) && defined(DEFAULT_I2C_BUS_SCL))
+#define BOARD_SECOND_I2C (defined(SECOND_I2C_BUS_SDA) && defined(SECOND_I2C_BUS_SCL))
 #define BOARD_SPI (defined(DEFAULT_SPI_BUS_SCK) && defined(DEFAULT_SPI_BUS_MISO) && defined(DEFAULT_SPI_BUS_MOSI))
 #define BOARD_UART (defined(DEFAULT_UART_BUS_RX) && defined(DEFAULT_UART_BUS_TX))
 

shared-bindings/board/__init__.c

@@ -28,7 +28,7 @@
 #include "py/runtime.h"
 
 #include "shared-bindings/board/__init__.h"
-#if BOARD_I2C
+#if defined(BOARD_I2C) || defined(BOARD_SECOND_I2C)
 #include "shared-bindings/busio/I2C.h"
 #endif
 #if BOARD_SPI
@@ -73,6 +73,30 @@ mp_obj_t board_i2c(void) {
 MP_DEFINE_CONST_FUN_OBJ_0(board_i2c_obj, board_i2c);
 
 
+//| def SECOND_I2C() -> busio.I2C:
+//|     """Returns the `busio.I2C` object for the secondary I2C pins, usually the STEMMA[QT] connector. It is a singleton."""
+//|     ...
+//|
+
+#if BOARD_SECOND_I2C
+mp_obj_t board_second_i2c(void) {
+    mp_obj_t singleton = common_hal_board_get_second_i2c();
+    if (singleton != NULL && !common_hal_busio_i2c_deinited(singleton)) {
+        return singleton;
+    }
+    assert_pin_free(SECOND_I2C_BUS_SDA);
+    assert_pin_free(SECOND_I2C_BUS_SCL);
+    return common_hal_board_create_second_i2c();
+}
+#else
+mp_obj_t board_second_i2c(void) {
+    mp_raise_NotImplementedError_varg(translate("No default %q bus"), MP_QSTR_SECOND_I2C);
+    return NULL;
+}
+#endif
+MP_DEFINE_CONST_FUN_OBJ_0(board_second_i2c_obj, board_second_i2c);
+
+
 //| def SPI() -> busio.SPI:
 //|     """Returns the `busio.SPI` object for the board designated SCK, MOSI and MISO pins. It is a
 //|     singleton."""

shared-bindings/board/__init__.h

@@ -39,6 +39,10 @@ mp_obj_t common_hal_board_get_i2c(void);
 mp_obj_t common_hal_board_create_i2c(void);
 MP_DECLARE_CONST_FUN_OBJ_0(board_i2c_obj);
 
+mp_obj_t common_hal_board_get_second_i2c(void);
+mp_obj_t common_hal_board_create_second_i2c(void);
+MP_DECLARE_CONST_FUN_OBJ_0(board_second_i2c_obj);
+
 mp_obj_t common_hal_board_get_spi(void);
 mp_obj_t common_hal_board_create_spi(void);
 MP_DECLARE_CONST_FUN_OBJ_0(board_spi_obj);

shared-module/board/__init__.c

@@ -67,6 +67,29 @@ mp_obj_t common_hal_board_create_i2c(void) {
 #endif
 
 
+#if BOARD_SECOND_I2C
+// Statically allocate the I2C object so it can live past the end of the heap and into the next VM.
+// That way it can be used by built-in I2CDisplay displays and be accessible through board.I2C().
+STATIC busio_i2c_obj_t second_i2c_obj;
+STATIC mp_obj_t second_i2c_singleton = NULL;
+
+mp_obj_t common_hal_board_get_second_i2c(void) {
+    return second_i2c_singleton;
+}
+
+mp_obj_t common_hal_board_create_second_i2c(void) {
+    // All callers have either already verified this or come so early that it can't be otherwise.
+    assert(second_i2c_singleton == NULL || common_hal_busio_i2c_deinited(second_i2c_singleton));
+    busio_i2c_obj_t *self = &second_i2c_obj;
+    self->base.type = &busio_i2c_type;
+
+    common_hal_busio_i2c_construct(self, SECOND_I2C_BUS_SCL, SECOND_I2C_BUS_SDA, 100000, 255);
+    second_i2c_singleton = (mp_obj_t)self;
+    return second_i2c_singleton;
+}
+#endif
+
+
 #if BOARD_SPI
 // Statically allocate the SPI object so it can live past the end of the heap and into the next VM.
 // That way it can be used by built-in FourWire displays and be accessible through board.SPI().
@@ -152,6 +175,23 @@ void reset_board_busses(void) {
         }
     }
     #endif
+    #if BOARD_SECOND_I2C
+    bool display_using_second_i2c = false;
+    #if CIRCUITPY_DISPLAYIO
+    for (uint8_t i = 0; i < CIRCUITPY_DISPLAY_LIMIT; i++) {
+        if (displays[i].bus_base.type == &displayio_i2cdisplay_type && displays[i].i2cdisplay_bus.bus == second_i2c_singleton) {
+            display_using_second_i2c = true;
+            break;
+        }
+    }
+    #endif
+    if (second_i2c_singleton != NULL) {
+        if (!display_using_second_i2c) {
+            common_hal_busio_i2c_deinit(second_i2c_singleton);
+            second_i2c_singleton = NULL;
+        }
+    }
+    #endif
     #if BOARD_SPI
     bool display_using_spi = false;
     #if CIRCUITPY_DISPLAYIO