cxadc is an alternative Linux driver for the Conexant CX2388x series of video decoder/encoder chips used on many PCI TV tuner and capture cards.

The new driver configures the CX2388x to capture in its raw output mode in 8-bit or 16-bit unsigned samples from the video input ports, allowing these cards to be used as a low-cost 28-54mhz 10bit ADC for SDR and similar applications.

Note! CX23885-xx & CX23888-xx are incompatible chips, however the CX25800 is a compatible chip.

Today the cheap PCIe (with 1x bridge chip) capture card market uses these chips at 25-35USD prices per card, directly from China.

The regular cx88 driver in Linux provides support for capturing composite video, digital video, audio and the other normal features of these chips.

Note! You shouldn't load both drivers at the same time.

Links to buy a CX Card White Variant / Green Variant / Blue Variant

Note 00: While Mhz is used and is accurate due to crystal used, in reality it should be called MSPS (million samples per second) as the actual effective sampling is half the Mhz number.

Note 01: The CX chip variant with the least self-noise is the cx23883, mostly found on the White Variation card; most clean captures are at 6dB off, and Digital Gain at 0-10.

Note 02: For reliable 40mhz 8-bit & 20mhz 16-bit samples, its recommended to replace the stock crystal with the ABLS2-40.000MHZ-D4YF-T.

For the full list of working crystal replacements, check the wiki page here!

Note 03: Asmedia PCI to PCIe 1x bridge chips may have support issues on some older PCH chipsets based on Intel 3rd gen; for example, white cards use ITE chips which might not have said issue.

Note 04: Added cooling can provide additional stability, more so with 40-54mhz crystal mods, but within 10° Celsius of room temperature is always preferable for silicone hardware. Currently only 40mhz crystal mods have been broadly viable in testing for current PCIe cards.

Note 05: For crystals over 54mhz: it might be possible to use higher crystals with self temperature regulated isolated chamber models, but this is still to have proper testing.

Note 06: While the term Mhz is used and is hardware accurate, to be clear with Nyquist sampling the crystal frequency should be noted as the MSPS or million samples per second rating, the number is always halved to equal its effective bandwidth of whatever its sampling i.e 28mhz is 28msps with 14mhz of bandwidth and so on you want a 2:1 ratio or higher of whatever your capturing to correctly sample it.

Note 07: When using a lower end older systems (Pentium 4 and before era), if there are not enough system resources, you may have dropped samples!

There is now a wiki about the cards variants and helpful information on modifications cabling and amplification.

Updated for Ubuntu 22.04

Update your package manager

sudo apt update 

Install build essentials

sudo apt install build-essential

Install Linux Headers

sudo apt install linux-headers-generic

Install PV for real-time monitoring of the runtime & datarate output:

sudo apt install pv

Install Sox key for manipulating data in real time or more usefully after captures:

sudo apt install sox

Install FFmpeg (If you don't already have it!)

sudo apt install ffmpeg

Install FLAC (If you don't already have it!)

sudo apt install flac 

Open the directory that you wish to install into, and git clone the repo source:

git clone https://github.com/happycube/cxadc-linux3 cxadc

For manual or offline use, click Code on the Github page and then download the zip. Move the zip where it's needed, and extract the files. Afterwards, open a terminal in said directory and continue below.

You can then use git pull inside the directory to update later then re-build the driver with the steps below again.

If not already inside of the CXADC directory

cd cxadc

Build and install the out-of-tree module:

make && sudo make modules_install && sudo depmod -a

If you see the following error, ignore it:

At main.c:160:
- SSL error:02001002:system library:fopen:No such file or directory: ../crypto/bio/bss_file.c:69
- SSL error:2006D080:BIO routines:BIO_new_file:no such file: ../crypto/bio/bss_file.c:76
sign-file: certs/signing_key.pem: No such file or directory
Warning: modules_install: missing 'System.map' file. Skipping depmod.

This error just means the module could not be signed. It will still be installed.

Install configuration files:

sudo cp cxadc.rules /etc/udev/rules.d
sudo cp cxadc.conf /etc/modprobe.d

Now reboot and the modules will be loaded automatically. The device node will be called /dev/cxadc0. The default cx88 driver will be blacklisted by cxadc.conf. Module parameters can also be configured in that file.

If there is an issue just re-load the CXADC module from the install directory via terminal

sudo rmmod cxadc
make
sudo make modules_install
sudo depmod -a

depmod -a enables auto load on start-up

If you see this error:

arch/x86/Makefile:142: CONFIG_X86_X32 enabled but no binutils support
  INSTALL /lib/modules/5.15.0-92-generic/extra/cxadc.ko
  SIGN    /lib/modules/5.15.0-92-generic/extra/cxadc.ko
  DEPMOD  /lib/modules/5.15.0-92-generic
Warning: modules_install: missing 'System.map' file. Skipping depmod.
make[1]: Leaving directory '/usr/src/linux-headers-5.15.0-92-generic'

Try Install Binutils

apt install binutils

If issues with binutills persists just use a diffrent Kernal like Xanmod has been tested and fixed the issue.

Check the utils folder and the associated README for quicker and more simplified commands.

To enable short system wide commands, first change into the utils directory from the cxadc source folder:

cd utils

Then install the system links with:

sudo ./inst_scripts

Then exit back to your main CXADC folder with:

cd.. 

Most of these parameters (except latency) can be changed using sysfs after the module has been loaded. Re-opening the device will update the CX2388x's registers. If you wish to be able to change module parameters as a regular users (e.g. without sudo), you need to run the command:

sudo usermod -a -G video YourUbuntuUserName

Parameters cannot be set with parameters specified in the kernel command line or with a configuration file such as one in /etc/modprobe.d. If you wish to make settings semi-permanent, see cxadc.rules for an example of setting a parameter on startup of udev.

To change configuration open the terminal and use the following command to change driver config settings.

Note! Use cxvalues to check your current configuration state at anytime.

X = Number Setting i.e 0 1 2 3 etc

Y = Parameter setting i.e vmux, level etc

echo X >/sys/class/cxadc/cxadc0/device/parameters/Y

Example: echo 1 >/sys/class/cxadc/cxadc0/device/parameters/vmux

NOTE: Also see the utils folders for scripts to manipulate these values; sudo will be required unless you add your local user to the video group as mentioned above.

In single card capture mode this is cat /dev/cxadc0

With multi card this will be cat /dev/cxadc1 and so on for card 2 and 3 etc

Same for parameters

sudo echo 1 >/sys/class/cxadc/cxadc0/device/parameters/vmux

This changes to

sudo echo 1 >/sys/class/cxadc/cxadc1/device/parameters/vmux

This can go up to 256 but in real world we don't expect more then 8-16 per system.

Check the Wiki for the optimal way to connect your card type!

A typical TV card has a tuner, a composite input with RCA/BNC ports and S-Video inputs tied to three of these inputs; you may need to experiment with inputs. The quickest way is to attach a video signal and see a white flash on signal hook-up, and change vmux until you get something.

Create a video preview of signal. Depending on the RF signal type, you will get an unstable video or just a white flash on cable hookup.

(Using video_size values to give approximately the correct resolution for the default 28.64 Mhz sample rate)

PAL:

sudo ffplay -hide_banner -async 1 -f rawvideo -pixel_format gray8 -video_size 1832x625 -i /dev/cxadc0 -vf scale=1135x625,eq=gamma=0.5:contrast=1.5

NTSC:

sudo ffplay -hide_banner -async 1 -f rawvideo -pixel_format gray8 -video_size 1820x525 -i /dev/cxadc0 -vf scale=910x525,eq=gamma=0.5:contrast=1.5

Some TV cards (e.g. the PixelView PlayTV Pro Ultra) have an external multiplexer attached to the CX2388x's GPIO pins to select an audio channel. If your card has one, you can select the input using this parameter.

On the PlayTV Pro Ultra:

• audsel=0: tuner tv audio out?
• audsel=1: silence?
• audsel=2: FM stereo tuner out?
• audsel=3: audio in to audio out

The PCI latency timer value for the device.

Enables or disables a default 6db gain applied to the input signal (Disabling this can result in cleaner capture but may require an external amplifier)

1 = On

0 = Off

The fixed digital gain to be applied by the CX2388x

(INT_VGA_VAL in the datasheet).

Adjust to minimise clipping; ./leveladj will do this for you automatically.

To change the card witch add the -h flag followed by the card so ./leveladj -h 1 for card 2 for example.

By default, cxadc captures at a rate of 8 x fsc (8 * 315 / 88 Mhz, approximately 28.6 MHz)

tenxfsc - Sets sampling rate of the ADC based on the crystal's native frequency

0 = Native crystal frequency i.e 28MHz (default), 40, 50, 54, (Modifyed etc)

1 = Native crystal frequency times 1.25

2 = Native crystal frequency times ~1.4

With the Stock 28Mhz Crystal the modes are the following:

0 = 28.6 MHz 8bit

1 = 35.8 MHz 8bit (Upsampled not recommended for use actual use)

2 = 40 MHz 8bit

Note!

40Mhz 8-bit & 20Mhz 16-bit modes have a very rare chance of working on stock non-modified cards, with the stock 28Mhz crystal.

It's recommended to physically replace the stock crystal with an 40/48/54Mhz fundamental crystal or external clock mod to achieve higher sample rate capture abbility and lower noise or multi card capture on the same clock source.

Alternatively, enter 2 digit values (like 20), that will then be multiplied by 1,000,000 (so 20 = 20,000,000sps), with the caveat that the lowest possible rate is a little more than 1/3 the actual HW Crystal rate (HW crystal / 40 * 14). For stock 28.6mhz crystal, this is about 10,022,728sps.

For a 40mhz crystal card, the lowest rate will be 14,000,000sps. The highest rate is capped at the 10fsc rate, or: HW crystal / 8 * 10.

Full range sample values can also be entered: 14318181 for instance. Again, the caveat is that the lowest possible rate is: HW crystal / 40 * 14 and the highest allowed rate is: HW crystal / 8 * 10.

Values outside the range will be converted to the lowest / highest value appropriately. Higher rates may work, with the max rate depending on individual card and cooling, but can cause system crash for others, so are prevented by the driver code (increase at your own risk).

By default, cxadc captures unsigned 8-bit samples.

In mode 1, unsigned 16-bit mode, the data is resampled (down-converted) by 50%

0 = 8xFsc 8-bit data mode (Raw Unsigned Data)

1 = 4xFsc 16-bit data mode (Filtered Vertical Blanking Interval Data)

When in 16bit sample modes, change to the following:

14.3 MHz 16-bit - Stock Card

17.9 MHz 16-bit - Stock Card

20 MHz 16-bit - Stock Card

The Mhz of the actual XTAL crystal affixed to the board. The stock crystal is usually 28636363 (28.6Mhz), but a 40mhz replacement crystal is easily available and crystals as high as 54mhz have been shown to work (with extra cooling required above 40mhz).

This value is ONLY used to compute the sample rates entered for the tenxfsc parameters other than 0, 1, 2.

This option allows you to manually adjust DC centre offset or the centring of the RF signal you wish to capture.

Manual calculation: If the "highest" and "lowest" values returned are equidistant from 0 and 255 respectively, it's centred.

Use leveladj to obtain level and centering information

./leveladj

Example:

low 121 high 133 clipped 0 nsamp 2097152

121-121=0 133+121 = 254 = centred, but: low

110 high 119 clipped 0 nsamp 2097152

110-110=0 119+110 = 229 = not centred.

Connect a live or playing signal to the input you've selected, and run leveladj to adjust the gain automatically:

./leveladj

To use this on multiple different cards

./leveladj -d 1 (1 means for device 2/3/4 and so on device 0 is assumed when -d is not used)

You can manually set a fixed gain setting after centering the signal with

sudo echo 0 >/sys/class/cxadc/cxadc0/device/parameters/level - Internal Gain (0~31)

sudo echo 0 >/sys/class/cxadc/cxadc0/device/parameters/sixdb - Digital Gain Boost (1 On / 0 Off)

If using an external amplifyer, set your gain 0 & sixdb 0 this also applys for CVBS RAW RF capture which can be tempermental.

Open a terminal in the directory you wish to write the data to, and use the following example command to capture 10 seconds of test samples.

timeout 10s cat /dev/cxadc0 |pv > CX_Card_28msps_8-bit.u8

Press Ctrl+C to copy then Ctrl+P to past the command use <+> to move edit position on the command line to edit the name or command and Enter to run the command.

cat is the defualt due to user issues with dd

To use the PV argument that enables datarate/runtime readout, modify the command command with |pv >

It will look like this when in use:

cat /dev/cxadc0 |pv > CX_Card_28msps_8-bit.u8
0:00:04 [38.1MiB/s] [        <=>  

Ctrl+C Will kill the current process, use this to stop the capture manually.

timeout 10s defines the capture duration of 10 seconds, this can be defined in hours minutes or seconds if a timeout duration is not set it will capture until storage space runs out or stopped manually.

sox -r 28636363 etc can be used to resample to the sample rate specified, whereas cat/dd will just do whatever has been pre-defined by parameters set above.

Note: For use with Tape-Decode, LaserDisc-Decode & CVBS-Decode projects, filetypes .u8 for 8-bit & .u16 for 16-bit samples are used instead of .raw extension.

• Windows Compression Scripts

• FLAC Compression Guide - CXADC Wiki

• FLAC Compression Guide - VHS-Decode Wiki

Optional but not optimal due to risk of dropped samples even with high end hardware etc, on the fly flac compressed captures are possible with the following commands; edit rates as needed.

8-bit Mode (Stock 28.6 MSPS)

cat /dev/cxadc0 | flac --fast -16 --sample-rate=28636 --sign=unsigned --channels=1 --endian=little --bps=8 --blocksize=65535 --lax -f - -o media-name-28msps-8bit-cx-card.flac

16-bit Mode (Stock 17.8 MSPS)

cat /dev/cxadc0 | flac --fast -16 --sample-rate=17898 --sign=unsigned --channels=1 --endian=little --bps=16 --blocksize=65535 --lax -f - -o media-name-17.8msps-16bit-cx-card.flac

cxadc was originally written by Hew How Chee ([email protected]). See SDR using a CX2388x TV+FM card for more details.

• added support for i2c, use i2c.c to tune
• set registers to lower gain
• set registers so that no signal is nearer to sample value 128
• added vmux and audsel as params during driver loading (for 2nd IF hardware modification, load driver using vmux=2). By default audsel=2 is to route tv tuner audio signal to audio out of TV card, vmux=1 to use the signal from video in of tv card.

• change code to compile and run in kernel 2.6.18 (Fedora Core 6) for Intel 32 bit single processor only
• clean up mess in version 0.2 code

This version has been retargeted for Ubuntu 13.10 Linux 3.11 by Chad Page ([email protected]).

While still a mess, the driver has been simplified a bit. Data is now read using standard read() semantics, so no capture program is needed like the original version.

For the first time, it also runs on 64-bit Linux, and seems to be OK under SMP.

• Update to work with Linux 5.1; older versions should still work.
• Tidy up the code to get rid of most of the warnings from checkpatch, and bring it closer in style to the normal cx88 driver.
• Make audsel optional.
• Don't allow /dev/cxadc to be opened multiple times.
• When unloading cxadc, reset the AGC registers to their default values. as cx88 expects. This lets you switch between cxadc and cx88 without rebooting.

Information Additions Documentation Cleanup by Harry Munday ([email protected])

• Change 10bit to the correct 16bit as that's what's stated in RAW16 under the datasheet and that's what the actual samples are in format-wise.
• Cleaned up and added examples for adjusting module parameters and basic real-time readout information.
• Added notations of ABLS2-40.000MHZ-D4YF-T a drop-in replacement crystal that adds 40mhz ability at low cost for current market PCIe cards.
• Added documentation for sixdb mode selection.
• Added links to find current CX cards
• Added issues that have been found
• Added crystal list of working replacements

New additions by Tony Anderson ([email protected])

• Fixed ./leveladj script from re-setting module parameters
• Added new command scripts
• Added new level adjustment tool cxlvlcavdd
• Added dedicated readme for new scripts and future tools

• Documentation Cleanup
• More utils additons
• Added cxlevel (utils/README.md)
• Added cxfreq (utils/README.md)
• Added cxvalues shows the current configuration.
• Added fortycryst 0 for no, 1 for yes, and then added sample rates 11-27 (14-27 on 40cryst)
• Added warning messages for high & low gain states

New multi-card support added by Adam R

• Multi card support up to 256 cards per system
• Individual card settings support
• Documentation & Scripts updated