Android Camera驱动相关参数学习

大家好，我是讯享网，很高兴认识大家。

https://www.freesion.com/article//
https://wenku.baidu.com/view/d335e7da647d27284a7351b7.html
http://www.360doc.com/content/20/1105/13/67063969_944236154.shtml

sensor全局曝光基本原理
全局曝光Sensor的所有行同时开始曝光，并同时结束曝光，在曝光结束后，Sensor将所有电子从感光区转到存储区，之后逐行地读出像素数据。这样曝光的好处是获得图像每一行的曝光时间比较一致，并且在拍摄运动物体时图像不会出现偏移和歪斜。
在这里插入图片描述
讯享网
H_Blank :扫描完一行后，行与行之间的返回过程称为水平消隐, 也叫行消隐
V_Blank :扫描完一帧后，从图像的右下角返回到左上角的过程称为垂直消隐, 也叫场消隐

H_Blank = line length pck - visible pixel width = Line blank Time
V_Blank = frame length lines - visible pixel height = Frame blank Time

line_length = Line Length pck (表示一行的长度，包含H_Blank)
frame_length = Frame Length lines(一帧的行数，包含V_Blank)

pclk : 控制像素输出的时钟(MHz)，表示是每个单位时间内采样的pixel数量，由MCLK经过PLL电路分频获得
fps = pclk / (frame_length * line_lenth) = 1 / (line_time * frame_length) （表示帧率）
line_time = line_length / pclk (表示曝光一行所需要的时间)

下面以hi1336 datasheet和驱动为例：
pll分频
pll寄存器

 //hi1336_setting.h 0x0734, 0x4b04, pll_mdiv = 4b = 75; vt_sys_div2 = 00 = 1; pll_prediv = 0010 = 3 (ramp) 0x0736, 0xd8b0, clk_div = 00 = 1; vt_sys_div1 = 011 = 4 (ramp) pclk = ramp_vt_sys_clk = 24 / pll_prediv * pll_mdiv / vt_sys_div1 / vt_sys_div2 = 24 /3 * 75 / 4 / 1 = 150 Mhz ... //hi1336_sensor.c static void set_dummy(void){ 
    LOG_INF("dummyline = %d, dummypixels = %d\n", imgsensor.dummy_line, imgsensor.dummy_pixel); write_cmos_sensor(0x020e, imgsensor.frame_length & 0xFFFF); write_cmos_sensor(0x0206, imgsensor.line_length/4); } 从寄存器中可以计算出pclk，MTK平台上驱动中set_dummy会对line_length处理(有些除4，有些除8); 所以对应pclk也会对应处理乘上对应的倍数 .cap = { 
    .pclk = , // 150*4 .linelength = 6004, .framelength = 3316, .startx = 0, .starty = 0, .grabwindow_width = 4208, .grabwindow_height = 3120, .mipi_data_lp2hs_settle_dc = 85, .max_framerate = 300, .mipi_pixel_rate = , }, .margin = 7, .min_shutter = 7, .mclk = 24, .mipi_lane_num = SENSOR_MIPI_4_LANE,

讯享网

mipi_pixel

讯享网 //hi1336_setting.h 0x0730, 0x770f, pll_mdiv = 77 = 119; vt_sys_div2 = 00 = 1; pll_prediv = 0011 = 4 (mipi) 0x0732, 0xe0b0, clk_div1 = 00 = 1; clk_div2 = 00 = 1; vt_sys_div1 = 100 = 5 (mipi) mipi_clk = mipi_bitrate_clk = 24 / pll_prediv * pll_mdiv / vt_sys_div1 / vt_sys_div2 = 24 / 4 * 119 / 1 / 1 = 714 Mhz mipi_pixel_rate = mipi_clk * 2 / raw_bits * lane_number (MIPI P N信号) = 714 * 2 / 10 * 4 = 571.2 Mhz ...

shutter

 根据shutter判断frame_length需要写多少 exposure_line = shutter = frame_length - dummy_line;(dummy_line 填充VBlank的行, 用于调整帧率) dummy_line = dummy_line > frame_offset ? dummy _line : frame_offset min_shutter <= shutter <= frame_length - frame_offset (frame_offset：最小的dummy_line) dummy_line = (pclk / fps / line_length) - frame_length = ( / 30 / 6004) - 3316 = 3331 - 3316 = 15 exposure_time = exposure_line * line_time 从datasheet中可以得知，写入fame_length和exposure_line的寄存器是24bit,即最大时0xffffff 所以理论曝光时间的最大值可以得出 exposure_time = (0xffffff - 7) * 10006 ns = 167s

讯享网 在暗的情况下，会增加曝光时间增加补偿亮度，当曝光时间超过当前vts的时候，曝光时间超过一帧的时间，这样会引起帧率降低 若要保持帧率可以增加gain值，MTK上gain主要分为isp gain(digital gain) sensor gain(analog gain) sensor gain + isp gain一般不能超过最大曝光时间,tunning调试AE曝光表参数中会有isp gain,一般最大在2x, 需要注意增加gain值都是优先使用analog gain，当analog gain增加到最大的时候，才会考虑使用digital gain

MTK平台上的write_shutter static void write_shutter(kal_uint32 shutter){ 
    ... spin_lock(&imgsensor_drv_lock); if(shutter > imgsensor.min_frame_length - imgsensor_info.margin) imgsensor.frame_length = shutter + imgsensor_info.margin; else imgsensor.frame_length = imgsensor.min_frame_length; if(imgsensor.frame_length > imgsensor_info.max_frame_length) imgsensor.frame_length = imgsensor_info.max_frame_length; spin_unlock(&imgsensor_drv_lock); ... } [collectParsedStrategyCaptureInfo] App set shutter =  (us)(1 s) [write_shutter] sshutter = 99930, imgsensor.frame_length = 99937, imgsensor.min_frame_length = 3331 [collectParsedStrategyCaptureInfo] App set shutter =  (us)(2 s) [write_shutter] shutter = , imgsensor.frame_length = , imgsensor.min_frame_length = 3331

同样展讯平台上，参数例如

讯享网 //Unisoc #define SNAPSHOT_TRIM_X 0 #define SNAPSHOT_TRIM_Y 0 #define SNAPSHOT_TRIM_W 4208 #define SNAPSHOT_TRIM_H 3120 #define EX_MCLK 24 #define LANE_NUM 4 #define SNAPSHOT_MIPI_PER_LANE_BPS 1152 #define SHAPSHOT_LINE_TIME 10006 #define SNAPSHOT_FRAME_LENGTH 3328 SHAPSHOT_LINE_TIME = linelength / pclk linelength = 10006 ns / 150 Mhz = 1500.9 ≈ 1501 SNAPSHOT_MIPI_PER_LANE_BPS = 2 * mipi_clk = 2 * 714 = 1428 (Mbps/lane) SNAPSHOT_FRAME_LENGTH = framelength = 3328 如果SHAPSHOT_LINE_TIME 错填的很大，会导致AE线性度fail，exposure_line变小，专业模式相同曝光时间下画面亮度会相差极大

Android Camera驱动相关参数学习

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