Add breakout-garden SPI slot selection for ST7789 displays

A new constructor has been added which accepts a enum type BG_SPI_SLOT which can be either:

ST7789::BG_SPI_FRONT or ST7789::BG_SPI_BACK.

This selects the correct CS/BL pins for the respective breakout-garden SPI slot.

Additionally the PWM'd backlight is turned *on* by default to avoid any confusion when the user does not set a value.

drivers/st7789/st7789.cpp

@@ -43,6 +43,7 @@ namespace pimoroni {
       pwm_set_wrap(pwm_gpio_to_slice_num(bl), 65535);
       pwm_init(pwm_gpio_to_slice_num(bl), &cfg, true);
       gpio_set_function(bl, GPIO_FUNC_PWM);
+      set_backlight(255); // Turn backlight on by default to avoid nasty surprises
     }
 
     // if auto_init_sequence then send initialisation sequence

drivers/st7789/st7789.hpp

@@ -30,16 +30,35 @@ namespace pimoroni {
     // frame buffer where pixel data is stored
     uint16_t *frame_buffer;
 
+    enum BG_SPI_SLOT {
+      BG_SPI_FRONT,
+      BG_SPI_BACK
+    };
+
   public:
+    ST7789(uint16_t width, uint16_t height, uint16_t *frame_buffer, BG_SPI_SLOT slot) :
+      width(width), height(height), frame_buffer(frame_buffer) {
+      switch(slot) {
+        case BG_SPI_FRONT:
+          cs = 17;
+          bl = 20;
+          break;
+        case BG_SPI_BACK:
+          cs = 22;
+          bl = 21;
+          break;
+      }
+    }
+
     ST7789(uint16_t width, uint16_t height, uint16_t *frame_buffer) :
       width(width), height(height), frame_buffer(frame_buffer) {}
 
     ST7789(uint16_t width, uint16_t height, uint16_t *frame_buffer,
            spi_inst_t *spi,
-           uint8_t cs, uint8_t dc, uint8_t sck, uint8_t mosi, uint8_t miso = -1) :
+           uint8_t cs, uint8_t dc, uint8_t sck, uint8_t mosi, uint8_t miso = -1, uint8_t bl = -1) :
       spi(spi),
       width(width), height(height),      
-      cs(cs), dc(dc), sck(sck), mosi(mosi), miso(miso), frame_buffer(frame_buffer) {}
+      cs(cs), dc(dc), sck(sck), mosi(mosi), miso(miso), bl(bl), frame_buffer(frame_buffer) {}
 
     void init(bool auto_init_sequence = true, bool round = false);
 

examples/breakout_roundlcd/demo.cpp

@@ -12,7 +12,7 @@ using namespace pimoroni;
 
 
 uint16_t buffer[BreakoutRoundLCD::WIDTH * BreakoutRoundLCD::HEIGHT];
-BreakoutRoundLCD display(buffer);
+BreakoutRoundLCD display(buffer, ST7789::BG_SPI_FRONT);
 
 constexpr float RADIUS = BreakoutRoundLCD::WIDTH / 2;
 
@@ -40,6 +40,7 @@ Pen from_hsv(float h, float s, float v) {
 
 int main() {
     display.init();
+    display.set_backlight(255);
 
     uint32_t steps = 70;
     float angle_step = 0.5f;
@@ -71,5 +72,6 @@ int main() {
         }
 
         display.update();
+        sleep_ms(10);
     }
 }

libraries/breakout_roundlcd/breakout_roundlcd.cpp

@@ -8,8 +8,12 @@ namespace pimoroni {
   }
 
   BreakoutRoundLCD::BreakoutRoundLCD(uint16_t *buf,  spi_inst_t *spi,
-      uint8_t cs, uint8_t dc, uint8_t sck, uint8_t mosi, uint8_t miso)
-    : PicoGraphics(WIDTH, HEIGHT, buf), screen(WIDTH, HEIGHT, buf, spi, cs, dc, sck, mosi, miso)  {
+      uint8_t cs, uint8_t dc, uint8_t sck, uint8_t mosi, uint8_t miso, uint8_t bl)
+    : PicoGraphics(WIDTH, HEIGHT, buf), screen(WIDTH, HEIGHT, buf, spi, cs, dc, sck, mosi, miso, bl)  {
+    __fb = buf;
+  }
+
+  BreakoutRoundLCD::BreakoutRoundLCD(uint16_t *buf,  ST7789::BG_SPI_SLOT slot) : PicoGraphics(WIDTH, HEIGHT, buf), screen(WIDTH, HEIGHT, buf, slot) {
     __fb = buf;
   }
 

libraries/breakout_roundlcd/breakout_roundlcd.hpp

@@ -12,7 +12,6 @@ namespace pimoroni {
   public:
     static const int WIDTH = 240;
     static const int HEIGHT = 240;
-    static const uint8_t PIN_UNUSED   = UINT8_MAX;
 
 
     //--------------------------------------------------
@@ -30,7 +29,8 @@ namespace pimoroni {
   public:
     BreakoutRoundLCD(uint16_t *buf);
     BreakoutRoundLCD(uint16_t *buf,  spi_inst_t *spi,
-      uint8_t cs, uint8_t dc, uint8_t sck, uint8_t mosi, uint8_t miso = PIN_UNUSED);
+      uint8_t cs, uint8_t dc, uint8_t sck, uint8_t mosi, uint8_t miso = -1, uint8_t bl = -1);
+    BreakoutRoundLCD(uint16_t *buf,  ST7789::BG_SPI_SLOT slot);
     
 
     //--------------------------------------------------