嵌入式 Linux 商用智慧屏开发实战：设备树、多媒体、OTA 升级整套项目精讲

/ {
    backlight: backlight {
        compatible = "pwm-backlight";
        pwms = <&pwm4 0 25000 0>;      /* PWM4, 25kHz */
        brightness-levels = <0 64 128 192 255>;
        default-brightness-level = <192>;
        enable-gpios = <&gpio1 RK_PB2 GPIO_ACTIVE_HIGH>;
    };

    panel: panel {
        compatible = "simple-panel";
        backlight = <&backlight>;
        power-supply = <&vcc3v3_lcd>;
        enable-gpios = <&gpio1 RK_PB1 GPIO_ACTIVE_HIGH>;
        reset-gpios  = <&gpio1 RK_PB0 GPIO_ACTIVE_LOW>;

        display-timings {
            native-mode = <&timing0>;
            timing0: timing0 {
                clock-frequency = <74250000>;   /* 像素时钟 74.25MHz */
                hactive = <1280>;  vactive = <800>;
                hfront-porch = <110>; hback-porch = <220>; hsync-len = <40>;
                vfront-porch = <5>;   vback-porch = <20>;  vsync-len = <5>;
                hsync-active = <0>;   vsync-active = <0>;
                de-active = <1>;      pixelclk-active = <0>;
            };
        };

        ports {
            port@0 {
                panel_in_lvds: endpoint {
                    remote-endpoint = <&lvds_out>;
                };
            };
        };
    };
};

&i2c4 {
    status = "okay";
    clock-frequency = <400000>;

    gt911: touchscreen@5d {
        compatible = "goodix,gt911";
        reg = <0x5d>;
        interrupt-parent = <&gpio3>;
        interrupts = <RK_PC0 IRQ_TYPE_EDGE_FALLING>;
        reset-gpios = <&gpio3 RK_PC1 GPIO_ACTIVE_LOW>;
        irq-gpios   = <&gpio3 RK_PC0 GPIO_ACTIVE_HIGH>;
        touchscreen-size-x = <1280>;
        touchscreen-size-y = <800>;
        status = "okay";
    };
};

# 查看设备树是否生效
cat /proc/device-tree/panel/display-timings/timing0/clock-frequency | xxd

# 检查触摸设备注册
dmesg | grep -i goodix
ls /dev/input/event*

# 触摸坐标校准验证
evtest /dev/input/event2

#include <rockchip/rk_mpi.h>

static MppCtx ctx;
static MppApi *mpi;

int vdec_init(void) {
    mpp_create(&ctx, &mpi);
    mpp_init(ctx, MPP_CTX_DEC, MPP_VIDEO_CodingHEVC);

    MppDecCfg cfg;
    mpp_dec_cfg_init(&cfg);
    mpi->control(ctx, MPP_DEC_GET_CFG, &cfg);
    cfg->base.split_parse = 1;          /* 硬件解码需分帧解析 */
    mpi->control(ctx, MPP_DEC_SET_CFG, &cfg);
    return 0;
}

/* 送帧解码循环 */
int vdec_push(MppPacket pkt, MppFrame *out) {
    if (mpi->decode_put_packet(ctx, pkt) != MPP_OK)
        return -EBUSY;
    if (mpi->decode_get_frame(ctx, out) != MPP_OK)
        return -EAGAIN;
    return 0;
}

snd_pcm_t *pcm;
snd_pcm_open(&pcm, "hw:0,0", SND_PCM_STREAM_PLAYBACK, 0);

snd_pcm_hw_params_t *params;
snd_pcm_hw_params_alloca(&params);
snd_pcm_hw_params_any(pcm, params);
snd_pcm_hw_params_set_access(pcm, params, SND_PCM_ACCESS_RW_INTERLEAVED);
snd_pcm_hw_params_set_format(pcm, params, SND_PCM_FORMAT_S16_LE);
snd_pcm_hw_params_set_rate(pcm, params, 48000, 0);
snd_pcm_hw_params_set_channels(pcm, params, 2);
snd_pcm_hw_params(pcm, params);

double diff = video_pts - audio_clock;
if (diff > 0.05) {
    usleep((useconds_t)(diff * 1e6));   /* 视频超前，等待 */
} else if (diff < -0.10) {
    av_frame_unref(frame);              /* 视频落后，丢帧 */
    continue;
}

| bootloader | boot_a | boot_b | rootfs_a | rootfs_b | userdata | misc |

#!/bin/sh
# ota_upgrade.sh —— 写入非活动分区并切换启动标志

set -e

ACTIVE_SLOT=$(fw_printenv -n active_slot)
if [ "$ACTIVE_SLOT" = "a" ]; then
    TARGET_SLOT="b"; TARGET_DEV="/dev/mmcblk0p6"
else
    TARGET_SLOT="a"; TARGET_DEV="/dev/mmcblk0p4"
fi

# 1. 校验包完整性（签名 + 哈希）
openssl dgst -sha256 -verify /etc/ota/pub.pem \
    -signature "$1.sig" "$1"

# 2. 写入非活动分区
dd if="$1" of="$TARGET_DEV" bs=4M conv=fsync status=progress

# 3. 标记分区待验证
fw_setenv boot_slot "$TARGET_SLOT"
fw_setenv boot_try 1

echo "OTA written to slot $TARGET_SLOT, reboot to verify"
sync && reboot

/* bootcount 超过阈值则回退到备用分区 */
if (env_get_ulong("boot_try", 10, 0) == 1) {
    env_set_ulong("boot_try", 0);
    env_set("boot_slot_try", env_get("boot_slot"));
    env_save();
} else if (env_get_ulong("bootcount", 10, 0) > 3) {
    /* 启动失败三次，回滚 */
    const char *rollback = strcmp(env_get("boot_slot"), "a") ?
                           "b" : "a";
    env_set("boot_slot", rollback);
    env_set_ulong("bootcount", 0);
    env_save();
}