cx88-devel.rst

  1.. SPDX-License-Identifier: GPL-2.0
  2
  3The cx88 driver
  4===============
  5
  6Author:  Gerd Hoffmann
  7
  8Documentation missing at the cx88 datasheet
  9-------------------------------------------
 10
 11MO_OUTPUT_FORMAT (0x310164)
 12
 13.. code-block:: none
 14
 15  Previous default from DScaler: 0x1c1f0008
 16  Digit 8: 31-28
 17  28: PREVREMOD = 1
 18
 19  Digit 7: 27-24 (0xc = 12 = b1100 )
 20  27: COMBALT = 1
 21  26: PAL_INV_PHASE
 22    (DScaler apparently set this to 1, resulted in sucky picture)
 23
 24  Digits 6,5: 23-16
 25  25-16: COMB_RANGE = 0x1f [default] (9 bits -> max 512)
 26
 27  Digit 4: 15-12
 28  15: DISIFX = 0
 29  14: INVCBF = 0
 30  13: DISADAPT = 0
 31  12: NARROWADAPT = 0
 32
 33  Digit 3: 11-8
 34  11: FORCE2H
 35  10: FORCEREMD
 36  9: NCHROMAEN
 37  8: NREMODEN
 38
 39  Digit 2: 7-4
 40  7-6: YCORE
 41  5-4: CCORE
 42
 43  Digit 1: 3-0
 44  3: RANGE = 1
 45  2: HACTEXT
 46  1: HSFMT
 47
 480x47 is the sync byte for MPEG-2 transport stream packets.
 49Datasheet incorrectly states to use 47 decimal. 188 is the length.
 50All DVB compliant frontends output packets with this start code.
 51
 52Hauppauge WinTV cx88 IR information
 53-----------------------------------
 54
 55The controls for the mux are GPIO [0,1] for source, and GPIO 2 for muting.
 56
 57====== ======== =================================================
 58GPIO0  GPIO1
 59====== ======== =================================================
 60  0        0    TV Audio
 61  1        0    FM radio
 62  0        1    Line-In
 63  1        1    Mono tuner bypass or CD passthru (tuner specific)
 64====== ======== =================================================
 65
 66GPIO 16(I believe) is tied to the IR port (if present).
 67
 68
 69From the data sheet:
 70
 71- Register 24'h20004  PCI Interrupt Status
 72
 73 - bit [18]  IR_SMP_INT Set when 32 input samples have been collected over
 74 - gpio[16] pin into GP_SAMPLE register.
 75
 76What's missing from the data sheet:
 77
 78- Setup 4KHz sampling rate (roughly 2x oversampled; good enough for our RC5
 79  compat remote)
 80- set register 0x35C050 to  0xa80a80
 81- enable sampling
 82- set register 0x35C054 to 0x5
 83- enable the IRQ bit 18 in the interrupt mask register (and
 84  provide for a handler)
 85
 86GP_SAMPLE register is at 0x35C058
 87
 88Bits are then right shifted into the GP_SAMPLE register at the specified
 89rate; you get an interrupt when a full DWORD is received.
 90You need to recover the actual RC5 bits out of the (oversampled) IR sensor
 91bits. (Hint: look for the 0/1and 1/0 crossings of the RC5 bi-phase data)  An
 92actual raw RC5 code will span 2-3 DWORDS, depending on the actual alignment.
 93
 94I'm pretty sure when no IR signal is present the receiver is always in a
 95marking state(1); but stray light, etc can cause intermittent noise values
 96as well.  Remember, this is a free running sample of the IR receiver state
 97over time, so don't assume any sample starts at any particular place.
 98
 99Additional info
100~~~~~~~~~~~~~~~
101
102This data sheet (google search) seems to have a lovely description of the
103RC5 basics:
104http://www.atmel.com/dyn/resources/prod_documents/doc2817.pdf
105
106This document has more data:
107http://www.nenya.be/beor/electronics/rc5.htm
108
109This document has a  how to decode a bi-phase data stream:
110http://www.ee.washington.edu/circuit_archive/text/ir_decode.txt
111
112This document has still more info:
113http://www.xs4all.nl/~sbp/knowledge/ir/rc5.htm