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Add auto-sleep/wake functionality with timer-based dimming

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- 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
2026-02-10 20:29:10 -05:00
parent b16211f148
commit 8cbb95b181
7 changed files with 384 additions and 7 deletions
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136
lib/st7796/st7796.c
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@@ -58,6 +58,7 @@
#include "hardware/gpio.h"
#include "hardware/spi.h"
#include "hardware/pwm.h"
#include "pico/binary_info.h"
#include "pico/stdlib.h"
@@ -118,6 +119,9 @@ static uint16_t width; // Display width in pixels (e.g., 480)
static uint16_t height; // Display height in pixels (e.g., 320)
static uint16_t x_offset; // X offset for display alignment (currently 0)
static uint16_t y_offset; // Y offset for display alignment (currently 0)
static uint8_t current_brightness = 100; // Current brightness level (0-100)
static uint pwm_slice; // PWM slice number for backlight control
static uint pwm_channel; // PWM channel number for backlight control
/**
* @brief Activate chip select (pull CS LOW)
@@ -359,12 +363,27 @@ void st7796_init(const struct st7796_config *c, uint16_t w, uint16_t h) {
gpio_init(config->gpio_rst);
gpio_set_dir(config->gpio_rst, GPIO_OUT);
// Initialize backlight pin
// Initialize backlight pin with PWM for brightness control
// Most TFT displays have LED backlights that need power
if (config->gpio_bl >= 0) {
gpio_init(config->gpio_bl);
gpio_set_dir(config->gpio_bl, GPIO_OUT);
gpio_put(config->gpio_bl, 1); // Turn on backlight immediately
// Configure GPIO for PWM function
gpio_set_function(config->gpio_bl, GPIO_FUNC_PWM);
// Find PWM slice and channel for this GPIO
pwm_slice = pwm_gpio_to_slice_num(config->gpio_bl);
pwm_channel = pwm_gpio_to_channel(config->gpio_bl);
// Configure PWM
// PWM frequency = clock_freq / (wrap + 1)
// We want ~1 kHz to avoid flicker: 125 MHz / 125000 = 1000 Hz
pwm_set_wrap(pwm_slice, 65535); // 16-bit resolution
pwm_set_clkdiv(pwm_slice, 1.907f); // 125 MHz / 1.907 / 65536 ≈ 1 kHz
// Start at full brightness
pwm_set_chan_level(pwm_slice, pwm_channel, 65535);
pwm_set_enabled(pwm_slice, true);
current_brightness = 100;
}
// Hardware reset sequence
@@ -934,3 +953,112 @@ void st7796_fill_triangle(uint16_t x0, uint16_t y0, uint16_t x1, uint16_t y1,
st7796_fill_rect(a, y, b - a + 1, 1, color);
}
}
/**
* @brief Set display brightness using PWM on backlight pin
*
* Controls the backlight LED brightness by adjusting the PWM duty cycle.
* The brightness parameter is a percentage that's converted to the
* appropriate PWM level (0-65535 for 16-bit PWM).
*
* Implementation:
* - brightness = 0: PWM level = 0 (backlight off)
* - brightness = 100: PWM level = 65535 (backlight fully on)
* - brightness = 50: PWM level = 32767 (50% duty cycle)
*
* The conversion formula: PWM_level = (brightness * 65535) / 100
*
* Human perception of brightness is logarithmic, but we use linear
* PWM for simplicity. For perceived linear brightness, a gamma
* correction curve could be applied.
*
* @param brightness Brightness level (0-100 percent)
*/
void st7796_set_brightness(uint8_t brightness) {
// Clamp brightness to valid range
if (brightness > 100) {
brightness = 100;
}
// Store current brightness
current_brightness = brightness;
// Convert percentage to 16-bit PWM level (0-65535)
// Using 32-bit intermediate to avoid overflow
uint32_t pwm_level = ((uint32_t)brightness * 65535) / 100;
// Set PWM duty cycle
if (config->gpio_bl >= 0) {
pwm_set_chan_level(pwm_slice, pwm_channel, (uint16_t)pwm_level);
}
}
/**
* @brief Get current display brightness level
*
* Returns the brightness level that was last set via st7796_set_brightness()
* or the default value (100) if brightness was never changed.
*
* @return Current brightness level (0-100 percent)
*/
uint8_t st7796_get_brightness(void) {
return current_brightness;
}
/**
* @brief Put display into sleep mode (low power)
*
* Enters deep sleep mode to minimize power consumption while maintaining
* initialization state. The framebuffer contents and all settings are
* preserved, so waking up is fast.
*
* Sleep sequence:
* 1. Turn off display (DISPOFF) - stops showing framebuffer
* 2. Enter sleep mode (SLPIN) - stops oscillator, minimal power
* 3. Turn off backlight - set PWM to 0
*
* Total power savings: Display draws ~10μA in sleep vs ~150mA active
* Touch controller on separate I2C bus remains fully functional
*/
void st7796_sleep(void) {
// Turn off display output first
write_command(ST7796_DISPOFF);
sleep_ms(10);
// Enter sleep mode (stops internal oscillator)
write_command(ST7796_SLPIN);
sleep_ms(120); // Wait for sleep mode to take effect (spec: 120ms)
// Turn off backlight to save power
if (config->gpio_bl >= 0) {
pwm_set_chan_level(pwm_slice, pwm_channel, 0);
}
}
/**
* @brief Wake display from sleep mode
*
* Exits sleep mode and restores display to full operation.
* All framebuffer contents and settings are preserved.
*
* Wake sequence:
* 1. Exit sleep mode (SLPOUT) - restarts oscillator
* 2. Wait for oscillator to stabilize (120ms)
* 3. Turn on display (DISPON) - starts showing framebuffer
* 4. Restore backlight to previous brightness
*/
void st7796_wake(void) {
// Exit sleep mode (restart oscillator)
write_command(ST7796_SLPOUT);
sleep_ms(120); // Wait for oscillator to stabilize (spec: 120ms)
// Turn on display output
write_command(ST7796_DISPON);
sleep_ms(10);
// Restore backlight to previous brightness level
if (config->gpio_bl >= 0) {
uint32_t pwm_level = ((uint32_t)current_brightness * 65535) / 100;
pwm_set_chan_level(pwm_slice, pwm_channel, (uint16_t)pwm_level);
}
}