Add auto-sleep/wake functionality with timer-based dimming
- Added PWM brightness control to ST7796 driver (0-100%) - Implemented hardware sleep mode for ST7796 (saves ~150mA) - Added sleep/wake functions preserving framebuffer and settings - Implemented timer-based inactivity detection (checks every 10s) - Auto-sleep after 5 minutes of no user input - Touch controller remains active during TFT sleep for instant wake - E-ink display also sleeps after timeout, requires re-init on wake - Added hardware_pwm library dependency to CMakeLists.txt - Brightness and sleep/wake methods exposed through display abstraction layer
This commit is contained in:
Adolfo Reyna
@@ -58,6 +58,7 @@
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#include "hardware/gpio.h"
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#include "hardware/spi.h"
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#include "hardware/pwm.h"
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#include "pico/binary_info.h"
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#include "pico/stdlib.h"
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@@ -118,6 +119,9 @@ static uint16_t width; // Display width in pixels (e.g., 480)
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static uint16_t height; // Display height in pixels (e.g., 320)
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static uint16_t x_offset; // X offset for display alignment (currently 0)
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static uint16_t y_offset; // Y offset for display alignment (currently 0)
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static uint8_t current_brightness = 100; // Current brightness level (0-100)
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static uint pwm_slice; // PWM slice number for backlight control
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static uint pwm_channel; // PWM channel number for backlight control
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/**
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* @brief Activate chip select (pull CS LOW)
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@@ -359,12 +363,27 @@ void st7796_init(const struct st7796_config *c, uint16_t w, uint16_t h) {
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gpio_init(config->gpio_rst);
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gpio_set_dir(config->gpio_rst, GPIO_OUT);
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// Initialize backlight pin
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// Initialize backlight pin with PWM for brightness control
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// Most TFT displays have LED backlights that need power
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if (config->gpio_bl >= 0) {
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gpio_init(config->gpio_bl);
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gpio_set_dir(config->gpio_bl, GPIO_OUT);
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gpio_put(config->gpio_bl, 1); // Turn on backlight immediately
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// Configure GPIO for PWM function
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gpio_set_function(config->gpio_bl, GPIO_FUNC_PWM);
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// Find PWM slice and channel for this GPIO
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pwm_slice = pwm_gpio_to_slice_num(config->gpio_bl);
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pwm_channel = pwm_gpio_to_channel(config->gpio_bl);
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// Configure PWM
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// PWM frequency = clock_freq / (wrap + 1)
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// We want ~1 kHz to avoid flicker: 125 MHz / 125000 = 1000 Hz
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pwm_set_wrap(pwm_slice, 65535); // 16-bit resolution
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pwm_set_clkdiv(pwm_slice, 1.907f); // 125 MHz / 1.907 / 65536 ≈ 1 kHz
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// Start at full brightness
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pwm_set_chan_level(pwm_slice, pwm_channel, 65535);
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pwm_set_enabled(pwm_slice, true);
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current_brightness = 100;
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}
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// Hardware reset sequence
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@@ -934,3 +953,112 @@ void st7796_fill_triangle(uint16_t x0, uint16_t y0, uint16_t x1, uint16_t y1,
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st7796_fill_rect(a, y, b - a + 1, 1, color);
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}
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}
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/**
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* @brief Set display brightness using PWM on backlight pin
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*
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* Controls the backlight LED brightness by adjusting the PWM duty cycle.
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* The brightness parameter is a percentage that's converted to the
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* appropriate PWM level (0-65535 for 16-bit PWM).
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*
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* Implementation:
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* - brightness = 0: PWM level = 0 (backlight off)
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* - brightness = 100: PWM level = 65535 (backlight fully on)
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* - brightness = 50: PWM level = 32767 (50% duty cycle)
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*
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* The conversion formula: PWM_level = (brightness * 65535) / 100
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*
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* Human perception of brightness is logarithmic, but we use linear
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* PWM for simplicity. For perceived linear brightness, a gamma
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* correction curve could be applied.
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*
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* @param brightness Brightness level (0-100 percent)
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*/
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void st7796_set_brightness(uint8_t brightness) {
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// Clamp brightness to valid range
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if (brightness > 100) {
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brightness = 100;
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}
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// Store current brightness
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current_brightness = brightness;
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// Convert percentage to 16-bit PWM level (0-65535)
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// Using 32-bit intermediate to avoid overflow
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uint32_t pwm_level = ((uint32_t)brightness * 65535) / 100;
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// Set PWM duty cycle
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if (config->gpio_bl >= 0) {
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pwm_set_chan_level(pwm_slice, pwm_channel, (uint16_t)pwm_level);
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}
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}
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/**
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* @brief Get current display brightness level
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*
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* Returns the brightness level that was last set via st7796_set_brightness()
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* or the default value (100) if brightness was never changed.
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*
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* @return Current brightness level (0-100 percent)
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*/
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uint8_t st7796_get_brightness(void) {
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return current_brightness;
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}
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/**
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* @brief Put display into sleep mode (low power)
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*
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* Enters deep sleep mode to minimize power consumption while maintaining
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* initialization state. The framebuffer contents and all settings are
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* preserved, so waking up is fast.
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*
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* Sleep sequence:
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* 1. Turn off display (DISPOFF) - stops showing framebuffer
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* 2. Enter sleep mode (SLPIN) - stops oscillator, minimal power
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* 3. Turn off backlight - set PWM to 0
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*
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* Total power savings: Display draws ~10μA in sleep vs ~150mA active
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* Touch controller on separate I2C bus remains fully functional
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*/
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void st7796_sleep(void) {
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// Turn off display output first
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write_command(ST7796_DISPOFF);
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sleep_ms(10);
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// Enter sleep mode (stops internal oscillator)
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write_command(ST7796_SLPIN);
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sleep_ms(120); // Wait for sleep mode to take effect (spec: 120ms)
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// Turn off backlight to save power
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if (config->gpio_bl >= 0) {
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pwm_set_chan_level(pwm_slice, pwm_channel, 0);
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}
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}
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/**
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* @brief Wake display from sleep mode
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*
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* Exits sleep mode and restores display to full operation.
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* All framebuffer contents and settings are preserved.
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*
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* Wake sequence:
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* 1. Exit sleep mode (SLPOUT) - restarts oscillator
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* 2. Wait for oscillator to stabilize (120ms)
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* 3. Turn on display (DISPON) - starts showing framebuffer
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* 4. Restore backlight to previous brightness
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*/
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void st7796_wake(void) {
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// Exit sleep mode (restart oscillator)
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write_command(ST7796_SLPOUT);
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sleep_ms(120); // Wait for oscillator to stabilize (spec: 120ms)
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// Turn on display output
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write_command(ST7796_DISPON);
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sleep_ms(10);
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// Restore backlight to previous brightness level
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if (config->gpio_bl >= 0) {
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uint32_t pwm_level = ((uint32_t)current_brightness * 65535) / 100;
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pwm_set_chan_level(pwm_slice, pwm_channel, (uint16_t)pwm_level);
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}
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}
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@@ -357,6 +357,93 @@ void st7796_draw_triangle(uint16_t x0, uint16_t y0, uint16_t x1, uint16_t y1, ui
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*/
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void st7796_fill_triangle(uint16_t x0, uint16_t y0, uint16_t x1, uint16_t y1, uint16_t x2, uint16_t y2, uint16_t color);
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/**
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* @brief Set display brightness using PWM on backlight pin
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*
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* Controls the backlight LED brightness using hardware PWM. The brightness
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* is specified as a percentage (0-100), where:
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* - 0 = Backlight completely off (minimum brightness)
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* - 100 = Backlight fully on (maximum brightness)
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* - Values in between = Proportional PWM duty cycle
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*
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* PWM Configuration:
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* - Frequency: 1000 Hz (1 kHz) - high enough to avoid flicker
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* - Resolution: 16-bit (0-65535 range internally)
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* - Smooth transitions without visible flickering
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*
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* Use cases:
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* - Power saving: Reduce brightness when idle
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* - Auto-dimming: Lower brightness after timeout
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* - Manual control: User brightness preferences
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* - Night mode: Very low brightness for dark environments
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*
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* @param brightness Brightness level (0-100 percent)
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* 0 = off, 100 = full brightness
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*
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* Performance: Instant - PWM is handled by hardware
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*
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* Note: Must be called after st7796_init() which configures the backlight pin
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*/
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void st7796_set_brightness(uint8_t brightness);
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/**
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* @brief Get current display brightness level
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*
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* Returns the currently configured brightness level as a percentage (0-100).
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* This reflects the last value set by st7796_set_brightness() or the
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* default value (100) if brightness was never explicitly set.
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*
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* @return Current brightness level (0-100 percent)
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*/
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uint8_t st7796_get_brightness(void);
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/**
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* @brief Put display into sleep mode (low power)
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*
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* Enters sleep mode to save power while keeping the controller initialized.
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* In sleep mode:
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* - Display is turned off (blank screen)
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* - Internal oscillator is stopped
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* - Framebuffer contents are preserved
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* - Backlight is turned off (PWM set to 0)
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* - Power consumption is minimized (~10μA typical)
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*
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* Touch controller remains active and functional since it's on a separate
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* I2C bus. Touch interrupts can wake the system from sleep.
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*
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* Use st7796_wake() to exit sleep mode and restore display.
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*
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* Commands sent:
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* - DISPOFF (0x28): Turn off display
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* - SLPIN (0x10): Enter sleep mode
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* - Backlight PWM set to 0
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*
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* Performance: ~120ms to enter sleep mode
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*/
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void st7796_sleep(void);
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/**
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* @brief Wake display from sleep mode
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*
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* Exits sleep mode and restores display to normal operation.
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* After waking:
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* - Internal oscillator restarts
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* - Display controller becomes active
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* - Framebuffer contents are preserved
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* - Display is turned on
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* - Backlight is restored to previous brightness
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*
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* Commands sent:
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* - SLPOUT (0x11): Exit sleep mode
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* - DISPON (0x29): Turn on display
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* - Backlight PWM restored to saved level
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*
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* Performance: ~120ms to fully wake up
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*
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* Note: Must call st7796_init() before first use of sleep/wake
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*/
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void st7796_wake(void);
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#ifdef __cplusplus
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}
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#endif
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