xref: /openbmc/linux/Documentation/driver-api/media/drivers/cx88-devel.rst (revision 4b4193256c8d3bc3a5397b5cd9494c2ad386317d)

.. SPDX-License-Identifier: GPL-2.0

The cx88 driver
===============

Author:  Gerd Hoffmann

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