Fix I2CDisplay lifecycle and splash lifecycle.

Fixes adafruit/Adafruit_CircuitPython_DisplayIO_SSD1306#2

Author: tannewt

py/circuitpy_mpconfig.h

@@ -273,13 +273,7 @@ extern const struct _mp_obj_module_t board_module;
 #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))
 
-#if BOARD_I2C
-#define BOARD_I2C_ROOT_POINTER mp_obj_t shared_i2c_bus;
-#else
-#define BOARD_I2C_ROOT_POINTER
-#endif
-
-// SPI is always allocated off the heap.
+// I2C and SPI are always allocated off the heap.
 
 #if BOARD_UART
 #define BOARD_UART_ROOT_POINTER mp_obj_t shared_uart_bus;
@@ -289,7 +283,6 @@ extern const struct _mp_obj_module_t board_module;
 
 #else
 #define BOARD_MODULE
-#define BOARD_I2C_ROOT_POINTER
 #define BOARD_UART_ROOT_POINTER
 #endif
 
@@ -647,7 +640,6 @@ extern const struct _mp_obj_module_t ustack_module;
     GAMEPAD_ROOT_POINTERS \
     mp_obj_t pew_singleton; \
     mp_obj_t terminal_tilegrid_tiles; \
-    BOARD_I2C_ROOT_POINTER \
     BOARD_UART_ROOT_POINTER \
     FLASH_ROOT_POINTERS \
     NETWORK_ROOT_POINTERS \

shared-module/board/__init__.c

@@ -40,17 +40,25 @@
 #endif
 
 #if BOARD_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 i2c_obj;
+STATIC mp_obj_t i2c_singleton = NULL;
+
 mp_obj_t common_hal_board_get_i2c(void) {
-    return MP_STATE_VM(shared_i2c_bus);
+    return i2c_singleton;
 }
 
 mp_obj_t common_hal_board_create_i2c(void) {
-    busio_i2c_obj_t *self = m_new_ll_obj(busio_i2c_obj_t);
+    if (i2c_singleton != NULL) {
+        return i2c_singleton;
+    }
+    busio_i2c_obj_t *self = &i2c_obj;
     self->base.type = &busio_i2c_type;
 
     common_hal_busio_i2c_construct(self, DEFAULT_I2C_BUS_SCL, DEFAULT_I2C_BUS_SDA, 400000, 0);
-    MP_STATE_VM(shared_i2c_bus) = MP_OBJ_FROM_PTR(self);
-    return MP_STATE_VM(shared_i2c_bus);
+    i2c_singleton = (mp_obj_t)self;
+    return i2c_singleton;
 }
 #endif
 
@@ -101,7 +109,18 @@ mp_obj_t common_hal_board_create_uart(void) {
 
 void reset_board_busses(void) {
 #if BOARD_I2C
-    MP_STATE_VM(shared_i2c_bus) = NULL;
+    bool display_using_i2c = false;
+    #if CIRCUITPY_DISPLAYIO
+    for (uint8_t i = 0; i < CIRCUITPY_DISPLAY_LIMIT; i++) {
+        if (displays[i].i2cdisplay_bus.bus == i2c_singleton) {
+            display_using_i2c = true;
+            break;
+        }
+    }
+    #endif
+    if (!display_using_i2c) {
+        i2c_singleton = NULL;
+    }
 #endif
 #if BOARD_SPI
     bool display_using_spi = false;

shared-module/displayio/Display.c

@@ -199,19 +199,26 @@ void common_hal_displayio_display_construct(displayio_display_obj_t* self,
 
 bool common_hal_displayio_display_show(displayio_display_obj_t* self, displayio_group_t* root_group) {
     if (root_group == NULL) {
-        root_group = &circuitpython_splash;
+        if (!circuitpython_splash.in_group) {
+            root_group = &circuitpython_splash;
+        } else if (self->current_group == &circuitpython_splash) {
+            return false;
+        }
     }
     if (root_group == self->current_group) {
         return true;
     }
-    if (root_group->in_group) {
+    if (root_group != NULL && root_group->in_group) {
         return false;
     }
     if (self->current_group != NULL) {
         self->current_group->in_group = false;
     }
-    displayio_group_update_transform(root_group, &self->transform);
-    root_group->in_group = true;
+
+    if (root_group != NULL) {
+        displayio_group_update_transform(root_group, &self->transform);
+        root_group->in_group = true;
+    }
     self->current_group = root_group;
     self->full_refresh = true;
     common_hal_displayio_display_refresh_soon(self);
@@ -402,6 +409,10 @@ void displayio_display_update_backlight(displayio_display_obj_t* self) {
 }
 
 void release_display(displayio_display_obj_t* self) {
+    if (self->current_group != NULL) {
+        self->current_group->in_group = false;
+    }
+
     if (self->backlight_pwm.base.type == &pulseio_pwmout_type) {
         common_hal_pulseio_pwmout_reset_ok(&self->backlight_pwm);
         common_hal_pulseio_pwmout_deinit(&self->backlight_pwm);

shared-module/displayio/__init__.c

@@ -163,7 +163,7 @@ void displayio_refresh_displays(void) {
 void common_hal_displayio_release_displays(void) {
     for (uint8_t i = 0; i < CIRCUITPY_DISPLAY_LIMIT; i++) {
         mp_const_obj_t bus_type = displays[i].fourwire_bus.base.type;
-        if (bus_type == NULL) {
+        if (bus_type == NULL || bus_type == &mp_type_NoneType) {
             continue;
         } else if (bus_type == &displayio_fourwire_type) {
             common_hal_displayio_fourwire_deinit(&displays[i].fourwire_bus);
@@ -235,12 +235,14 @@ void reset_displays(void) {
             // Not an active display.
             continue;
         }
+    }
 
+    for (uint8_t i = 0; i < CIRCUITPY_DISPLAY_LIMIT; i++) {
         // Reset the displayed group. Only the first will get the terminal but
         // that's ok.
         displayio_display_obj_t* display = &displays[i].display;
         display->auto_brightness = true;
-        common_hal_displayio_display_show(display, &circuitpython_splash);
+        common_hal_displayio_display_show(display, NULL);
     }
 }