Refactor power saving logic into display drivers and add ST7789 support

lib/st7789/st7789.c

@@ -12,6 +12,7 @@
 
 #include "hardware/gpio.h"
 #include "hardware/spi.h"
+#include "hardware/pwm.h"
 #include "pico/binary_info.h"
 #include "pico/stdlib.h"
 
@@ -60,6 +61,12 @@ static uint16_t height;
 static uint16_t x_offset;
 static uint16_t y_offset;
 
+// Backlight control
+static uint pwm_slice;
+static uint pwm_channel;
+static uint8_t current_brightness = 100;
+static bool pwm_initialized = false;
+
 static inline void cs_select() {
     if (config->gpio_cs >= 0) {
         asm volatile("nop \n nop \n nop");
@@ -173,10 +180,19 @@ void st7789_init(const struct st7789_config *c, uint16_t w, uint16_t h) {
     gpio_init(config->gpio_rst);
     gpio_set_dir(config->gpio_rst, GPIO_OUT);
 
-    // Initialize backlight pin
-    gpio_init(config->gpio_bl);
-    gpio_set_dir(config->gpio_bl, GPIO_OUT);
-    gpio_put(config->gpio_bl, 1); // Turn on backlight
+    // Initialize backlight pin with PWM
+    if (config->gpio_bl >= 0) {
+        gpio_set_function(config->gpio_bl, GPIO_FUNC_PWM);
+        pwm_slice = pwm_gpio_to_slice_num(config->gpio_bl);
+        pwm_channel = pwm_gpio_to_channel(config->gpio_bl);
+        
+        // Set PWM frequency to ~1kHz
+        pwm_set_wrap(pwm_slice, 65535);
+        pwm_set_chan_level(pwm_slice, pwm_channel, 65535); // 100% duty cycle
+        pwm_set_enabled(pwm_slice, true);
+        
+        pwm_initialized = true;
+    }
 
     // Reset display
     reset_pulse();
@@ -403,3 +419,48 @@ void st7789_draw_line(uint16_t x0, uint16_t y0, uint16_t x1, uint16_t y1, uint16
         }
     }
 }
+
+void st7789_set_brightness(uint8_t brightness) {
+    if (!pwm_initialized || config->gpio_bl < 0) return;
+    
+    // Clamp brightness
+    if (brightness > 100) brightness = 100;
+    
+    current_brightness = brightness;
+    
+    // Convert 0-100 to 0-65535
+    uint16_t level = (uint16_t)((brightness * 65535) / 100);
+    pwm_set_chan_level(pwm_slice, pwm_channel, level);
+}
+
+uint8_t st7789_get_brightness(void) {
+    return current_brightness;
+}
+
+void st7789_sleep(void) {
+    // Turn off backlight
+    if (pwm_initialized && config->gpio_bl >= 0) {
+        pwm_set_chan_level(pwm_slice, pwm_channel, 0);
+    }
+    
+    // Display off
+    write_command(ST7789_DISPOFF);
+    sleep_ms(10);
+    
+    // Sleep in
+    write_command(ST7789_SLPIN);
+    sleep_ms(120);
+}
+
+void st7789_wake(void) {
+    // Sleep out
+    write_command(ST7789_SLPOUT);
+    sleep_ms(120);
+    
+    // Display on
+    write_command(ST7789_DISPON);
+    sleep_ms(10);
+    
+    // Restore brightness
+    st7789_set_brightness(current_brightness);
+}

lib/st7789/st7789.h

@@ -38,6 +38,11 @@ void st7789_draw_circle(uint16_t x0, uint16_t y0, uint16_t r, uint16_t color);
 void st7789_fill_circle(uint16_t x0, uint16_t y0, uint16_t r, uint16_t color);
 void st7789_draw_line(uint16_t x0, uint16_t y0, uint16_t x1, uint16_t y1, uint16_t color);
 
+void st7789_sleep(void);
+void st7789_wake(void);
+void st7789_set_brightness(uint8_t brightness);
+uint8_t st7789_get_brightness(void);
+
 #ifdef __cplusplus
 }
 #endif