first commit

main/drivers/backlight/backlight.c

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+/*
+ * STC8H1K28 board controller, CrowPanel 7" Advance v1.3.
+ *
+ * A small 8051-class MCU sitting on the I2C bus at 0x30. It drives the LCD
+ * backlight and, critically, the GT911 reset line -- there is no ESP32 GPIO
+ * for touch reset on this board, so the GT911 stays mute until the sequence
+ * below has run.
+ *
+ * Protocol is single raw bytes, no register addressing:
+ *   0x19          wake
+ *   0x10, 0x18    configure / release GT911 from reset
+ *   0x00 - 0xF5   brightness, INVERTED (0x00 = full, 0xF5 = off)
+ *
+ * v1.2 boards use a different, narrower range (0x05 = off .. 0x10 = max).
+ */
+
+#include "esp_check.h"
+#include "esp_log.h"
+#include "freertos/FreeRTOS.h"
+#include "freertos/task.h"
+
+#include "backlight.h"
+#include "i2c_bus.h"
+
+static const char *TAG = "backlight";
+
+#define STC8_ADDR        0x30
+#define STC8_I2C_HZ      100000
+#define STC8_TIMEOUT_MS  100
+
+#define STC8_CMD_WAKE    0x19
+#define STC8_CMD_CFG1    0x10
+#define STC8_CMD_CFG2    0x18
+
+/* Inverted brightness range. */
+#define STC8_DUTY_MAX_ON  0x00
+#define STC8_DUTY_OFF     0xF5
+
+static i2c_master_dev_handle_t dev = NULL;
+
+static esp_err_t stc8_cmd(uint8_t cmd)
+{
+    return i2c_master_transmit(dev, &cmd, 1, STC8_TIMEOUT_MS);
+}
+
+esp_err_t backlight_init(void)
+{
+    const i2c_device_config_t cfg = {
+        .dev_addr_length = I2C_ADDR_BIT_LEN_7,
+        .device_address = STC8_ADDR,
+        .scl_speed_hz = STC8_I2C_HZ,
+    };
+    ESP_RETURN_ON_ERROR(i2c_master_bus_add_device(i2c_bus_get(), &cfg, &dev), TAG,
+                        "could not add STC8H1K28 at 0x%02X", STC8_ADDR);
+
+    ESP_RETURN_ON_ERROR(stc8_cmd(STC8_CMD_WAKE), TAG, "wake failed");
+    vTaskDelay(pdMS_TO_TICKS(10));
+
+    /* These two also release the GT911 from reset. */
+    ESP_RETURN_ON_ERROR(stc8_cmd(STC8_CMD_CFG1), TAG, "config 1 failed");
+    vTaskDelay(pdMS_TO_TICKS(10));
+
+    ESP_RETURN_ON_ERROR(stc8_cmd(STC8_CMD_CFG2), TAG, "config 2 failed");
+    vTaskDelay(pdMS_TO_TICKS(100));
+
+    ESP_LOGI(TAG, "STC8H1K28 initialized (GT911 released from reset)");
+    return ESP_OK;
+}
+
+esp_err_t backlight_set(uint8_t brightness)
+{
+    if (dev == NULL) {
+        return ESP_ERR_INVALID_STATE;
+    }
+
+    /* Map 0..255 (intuitive) onto 0xF5..0x00 (wire, inverted). */
+    const uint8_t duty = (uint8_t)(STC8_DUTY_OFF -
+                                   ((uint32_t)brightness * STC8_DUTY_OFF) / 255);
+    return stc8_cmd(duty);
+}

main/drivers/backlight/backlight.h

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+#ifndef BACKLIGHT_H
+#define BACKLIGHT_H
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#include "esp_err.h"
+
+/*
+ * STC8H1K28 board controller (I2C 0x30) on the CrowPanel 7" Advance.
+ *
+ * It owns more than the backlight: its init sequence also drives the GT911
+ * reset line, so this must run before the touch controller will answer on
+ * the bus at all. Requires i2c_bus_init() first.
+ */
+esp_err_t backlight_init(void);
+
+/* 0 = off, 255 = full. The v1.3 wire protocol is inverted; that is handled
+ * internally so callers can use the intuitive direction. */
+esp_err_t backlight_set(uint8_t brightness);
+
+#endif