Device tree (pix_clk_hz) setting for xavier nx - camera input

shahabadi.p · October 19, 2024, 6:35am

I would like to know how to calculate the correct pix_clk_hz setting in the device tree.
See below for details.
In the application we are developing, the adv7481’s CSI-2 output is connected to the Xavier nx’s CSI-2 input. D-PHY x 4 lanes are used. The data format is YUV 8-bit.
First of all, as an experiment, I tried transferring some images from the adv7481 to xavier at 1280*720p (50FPS), and there was no problem to capture the images. (The ADV7481 register’s set on SDR mode). The device tree and setting value at this time was :
mode0 { // ADV7481_MODE_1280x720_50FPS_4LANES
mclk_khz = “74250”;
num_lanes = “4”;
tegra_sinterface = “serial_a”;
phy_mode = “DPHY”;
discontinuous_clk = “yes”;
dpcm_enable = “false”;
cil_settletime = “0”;
active_w = “1280”;
active_h = “720”;

			mode_type = "yuv";
                			pixel_phase = "uyvy";
                			csi_pixel_bit_depth = "8";
			pixel_t  = "yuv_uyvy16";
			readout_orientation = "90";
			line_length = "3448";
			inherent_gain = "1";
			
			mclk_multiplier = "4";
			pix_clk_hz = "297000000";
		
			gain_factor = "16";
			framerate_factor = "1000000";
			exposure_factor = "1000000";
			min_gain_val = "16"; 
			max_gain_val = "170"; 
			step_gain_val = "1";
			default_gain = "16"; 
			min_hdr_ratio = "1";
			max_hdr_ratio = "1";
			min_framerate = "1500000"; 
			max_framerate = "120000000"; 
			step_framerate = "1";
			default_framerate = "50000000"; 
			min_exp_time = "13"; 
			max_exp_time = "683709"; 
			step_exp_time = "1";
			default_exp_time = "2495";
			embedded_metadata_height = "0";
		};

Then I changed the camera input resplution to 1920*1080p (30FPS), and there was no problem to capture the images. (The ADV7481 register’s set on SDR mode). The device tree and setting value at this time was :
mode1 { // ADV7481_MODE_1920x1080_30FPS_4LANES
mclk_khz = “74250”;
num_lanes = “4”;
tegra_sinterface = “serial_a”;
phy_mode = “DPHY”;
discontinuous_clk = “yes”;
dpcm_enable = “false”;
cil_settletime = “0”;

			active_w = "1920";
			active_h = "1080";
			mode_type = "yuv";
                			pixel_phase = "uyvy";
                			csi_pixel_bit_depth = "8";
			pixel_t  = "yuv_uyvy16";
			readout_orientation = "90";
			line_length = "3448";				
			inherent_gain = "1";

			mclk_multiplier = "4";
			pix_clk_hz = "297000000";
			
			gain_factor = "16";
			framerate_factor = "1000000";
			exposure_factor = "1000000";
			min_gain_val = "16"; 
			max_gain_val = "170";
			step_gain_val = "1";
			default_gain = "16";
			min_hdr_ratio = "1";
			max_hdr_ratio = "1";
			min_framerate = "1500000"; 
			max_framerate = "120000000"; 
			step_framerate = "1";
			default_framerate = "30000000"; 
			min_exp_time = "13";
			max_exp_time = "683709";
			step_exp_time = "1";
			default_exp_time = "2495";
			embedded_metadata_height = "0";
		};

finally I want to have the camera input resolution 1920*1080(50FPS), and could not capture the images with any setting of device tree. (The ADV7481 register’s set on SDR mode). The device tree and setting value at this time was :
mode2 { // ADV7481_MODE_1920x1080_50FPS_4LANES
mclk_khz = “148500”;
num_lanes = “4”;
tegra_sinterface = “serial_a”;
phy_mode = “DPHY”;
discontinuous_clk = “yes”;
dpcm_enable = “false”;
cil_settletime = “0”;
active_w = “1920”;
active_h = “1080”;

			mode_type = "yuv";
                			pixel_phase = "uyvy";
                			csi_pixel_bit_depth = "8";
			pixel_t  = "yuv_uyvy16";
			readout_orientation = "90";
			line_length = "3448";				
			inherent_gain = "1";

			mclk_multiplier = "4";		
			pix_clk_hz = "594000000";	
			
			gain_factor = "16";
			framerate_factor = "1000000";
			exposure_factor = "1000000";
			min_gain_val = "16"; 
			max_gain_val = "170";
			step_gain_val = "1";
			default_gain = "16";
			min_hdr_ratio = "1";
			max_hdr_ratio = "1";				
			min_framerate = "1500000"; 
			max_framerate = "120000000"; 
			step_framerate = "1";
			default_framerate = "50000000"; 
			min_exp_time = "13"; 
			max_exp_time = "683709"; 
			step_exp_time = "1";
			default_exp_time = "2495";
			embedded_metadata_height = "0";
		};

I tried the following settings but none of them were successful:
• I test the changed the pix_clk_hz setting value to 1250000000. (xavier nx series : 14 lanes - 2.5 Gb/s per pair, total up to 30 Gbps)
pixel_clk_hz = sensor data rate per lane (Mbps) * number of lanes / bits per pixel
pixel_clk_hz = (2.500.000.000 / 8 )* 4 = 1.250.000.000 bps
• I test the changed the pix_clk_hz setting value to 1250000000. ( sensor output size =22001125 )
pixel_clk_hz = sensor output size × frame rate
pixel_clk_hz = (22001125 )* 50= 123.750.000 bps
• I changed the ADV7481 register’s to DDR mode.
Which part am I doing wrong?
Thank you in advance for your cooperation.

JerryChang · October 21, 2024, 2:37am

hello shahabadi.p,

here’s another example to check with CSI date rate, for example, 4K(3840x2160),90-fps,10-bit.
CSI data-rate = 3840 * 2160 * 10 * 90 * 1.15 (15% overhead) ~= 8.584 Gbps
so… device tree configuration, pixel_clk_hz = 8600000000;

shahabadi.p · October 21, 2024, 8:03am

Hello JerryChang,

Thanks for the reply.
Please give an example also from mclk_khz (Standard MIPI driving clock frequency, in kilohertz).
Should the value of mclk_khz be changed in different mode with different resolutions?

shahabadi.p · October 21, 2024, 8:09am

And one more question about mclk_multiplier :
(mclk_multiplier : Deprecated. This switch is no longer needed because the value it specifies is calculated internally.)
Is it possible to delete this item by considering these explanations?

JerryChang · October 21, 2024, 8:26am

hello shahabadi.p,

BTW,
it might be the issue that driver side select incorrect settings, since you have two 1920x1080 sensor modes, i.e. 30-fps and 50-fps.
please refer to developer guide, Device Properties by adding use_sensor_mode_id = "true"; for sensor mode selection.

here’s sample pipeline for mode selection.
$ v4l2-ctl -d /dev/video0 --set-fmt-video=width=1280,height=720,pixelformat=RG10 --set-ctrl bypass_mode=0 --set-ctrl sensor_mode=4 --stream-mmap --stream-count=100

shahabadi.p · October 23, 2024, 11:00am

Hi Jerry,
It seems that the problem is in this part:
(8-BIT DIGITAL INPUT/OUTPUT PORT OF ADV7481:
The maximum input and output video resolution supported is 720p/1080i in both SDR and DDR modes.)

But, please answer my previous two questions (about : mclk_khz & mclk_multiplier ) to make me clear about the device tree correct configuration.
Thank you so much.

JerryChang · October 24, 2024, 2:17am

hello shahabadi.p,

this property has deprecated, it’s now using camera settings (i.e. pix_clk_hz, num_lanes, bit_depth…etc) to initialize camera software configuration internally.

when you configure cil_settletime = 0; it’s picking up mclk_khz and pix_clk_hz to do auto calibrate.

shahabadi.p · October 30, 2024, 6:28am

Hi Jerry,
Thanks a lot for the all replies.

system · November 20, 2024, 5:55am

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Device tree (pix_clk_hz) setting for xavier nx - camera input

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