.. SPDX-License-Identifier: GPL-2.0
The cx88 driver
===============
Author: Gerd Hoffmann
This is a v4l2 device driver for the cx2388x chip.
Current status
--------------
video
- Works.
- Overlay isn't supported.
audio
- 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.
vbi
- Works.
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:
.. code-block:: none
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
Documentation missing at the cx88 datasheet
-------------------------------------------
MO_OUTPUT_FORMAT (0x310164)
.. code-block:: none
Previous default from DScaler: 0x1c1f0008
Digit 8: 31-28
28: PREVREMOD = 1
Digit 7: 27-24 (0xc = 12 = b1100 )
27: COMBALT = 1
26: PAL_INV_PHASE
(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
12: NARROWADAPT = 0
Digit 3: 11-8
11: FORCE2H
10: FORCEREMD
9: NCHROMAEN
8: NREMODEN
Digit 2: 7-4
7-6: YCORE
5-4: CCORE
Digit 1: 3-0
3: RANGE = 1
2: HACTEXT
1: HSFMT
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.
Hauppauge WinTV cx88 IR information
-----------------------------------
The controls for the mux are GPIO [0,1] for source, and GPIO 2 for muting.
====== ======== =================================================
GPIO0 GPIO1
====== ======== =================================================
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.
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