12. The cx88 driver

Author: Gerd Hoffmann

This is a v4l2 device driver for the cx2388x chip.

12.1. Current status

  • Works.
  • Overlay isn’t supported.
  • Works. The TV standard detection is made by the driver, as the hardware has bugs to auto-detect.
  • audio data dma (i.e. recording without loopback cable to the sound card) is supported via cx88-alsa.
  • Works.

12.2. How to add support for new cards

The driver needs some config info for the TV cards. This stuff is in cx88-cards.c. If the driver doesn’t work well you likely need a new entry for your card in that file. Check the kernel log (using dmesg) to see whenever the driver knows your card or not. There is a line like this one:

cx8800[0]: subsystem: 0070:3400, board: Hauppauge WinTV \
        34xxx models [card=1,autodetected]

If your card is listed as “board: UNKNOWN/GENERIC” it is unknown to the driver. What to do then?

  1. Try upgrading to the latest snapshot, maybe it has been added meanwhile.

  2. You can try to create a new entry yourself, have a look at cx88-cards.c. If that worked, mail me your changes as unified diff (“diff -u”).

  3. Or you can mail me the config information. We need at least the following information to add the card:

    • the PCI Subsystem ID (“0070:3400” from the line above, “lspci -v” output is fine too).
    • the tuner type used by the card. You can try to find one by trial-and-error using the tuner=<n> insmod option. If you know which one the card has you can also have a look at the list in CARDLIST.tuner

12.3. Documentation missing at the cx88 datasheet


Previous default from DScaler: 0x1c1f0008
Digit 8: 31-28

Digit 7: 27-24 (0xc = 12 = b1100 )
27: COMBALT = 1
  (DScaler apparently set this to 1, resulted in sucky picture)

Digits 6,5: 23-16
25-16: COMB_RANGE = 0x1f [default] (9 bits -> max 512)

Digit 4: 15-12
15: DISIFX = 0
14: INVCBF = 0
13: DISADAPT = 0

Digit 3: 11-8

Digit 2: 7-4
7-6: YCORE
5-4: CCORE

Digit 1: 3-0
3: RANGE = 1

0x47 is the sync byte for MPEG-2 transport stream packets. Datasheet incorrectly states to use 47 decimal. 188 is the length. All DVB compliant frontends output packets with this start code.

12.4. Hauppauge WinTV cx88 IR information

The controls for the mux are GPIO [0,1] for source, and GPIO 2 for muting.

0 0 TV Audio
1 0 FM radio
0 1 Line-In
1 1 Mono tuner bypass or CD passthru (tuner specific)

GPIO 16(I believe) is tied to the IR port (if present).

From the data sheet:

  • Register 24’h20004 PCI Interrupt Status
  • bit [18] IR_SMP_INT Set when 32 input samples have been collected over
  • gpio[16] pin into GP_SAMPLE register.

What’s missing from the data sheet:

  • Setup 4KHz sampling rate (roughly 2x oversampled; good enough for our RC5 compat remote)
  • set register 0x35C050 to 0xa80a80
  • enable sampling
  • set register 0x35C054 to 0x5
  • enable the IRQ bit 18 in the interrupt mask register (and provide for a handler)

GP_SAMPLE register is at 0x35C058

Bits are then right shifted into the GP_SAMPLE register at the specified rate; you get an interrupt when a full DWORD is received. You need to recover the actual RC5 bits out of the (oversampled) IR sensor bits. (Hint: look for the 0/1and 1/0 crossings of the RC5 bi-phase data) An actual raw RC5 code will span 2-3 DWORDS, depending on the actual alignment.

I’m pretty sure when no IR signal is present the receiver is always in a marking state(1); but stray light, etc can cause intermittent noise values as well. Remember, this is a free running sample of the IR receiver state over time, so don’t assume any sample starts at any particular place.

12.4.1. Additional info

This data sheet (google search) seems to have a lovely description of the RC5 basics: http://www.atmel.com/dyn/resources/prod_documents/doc2817.pdf

This document has more data: http://www.nenya.be/beor/electronics/rc5.htm

This document has a how to decode a bi-phase data stream: http://www.ee.washington.edu/circuit_archive/text/ir_decode.txt

This document has still more info: http://www.xs4all.nl/~sbp/knowledge/ir/rc5.htm