linux/Documentation/video4linux/hauppauge-wintv-cx88-ir.txt
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   1The controls for the mux are GPIO [0,1] for source, and GPIO 2 for muting.
   2
   3GPIO0  GPIO1
   4  0        0    TV Audio
   5  1        0    FM radio
   6  0        1    Line-In
   7  1        1    Mono tuner bypass or CD passthru (tuner specific)
   8
   9GPIO 16(i believe) is tied to the IR port (if present).
  10
  11------------------------------------------------------------------------------------
  12
  13>From the data sheet:
  14 Register 24'h20004  PCI Interrupt Status
  15  bit [18]  IR_SMP_INT Set when 32 input samples have been collected over
  16  gpio[16] pin into GP_SAMPLE register.
  17
  18What's missing from the data sheet:
  19
  20Setup 4KHz sampling rate (roughly 2x oversampled; good enough for our RC5
  21compat remote)
  22set register 0x35C050 to  0xa80a80
  23
  24enable sampling
  25set register 0x35C054 to 0x5
  26
  27Of course, enable the IRQ bit 18 in the interrupt mask register .(and
  28provide for a handler)
  29
  30GP_SAMPLE register is at 0x35C058
  31
  32Bits are then right shifted into the GP_SAMPLE register at the specified
  33rate; you get an interrupt when a full DWORD is received.
  34You need to recover the actual RC5 bits out of the (oversampled) IR sensor
  35bits. (Hint: look for the 0/1and 1/0 crossings of the RC5 bi-phase data)  An
  36actual raw RC5 code will span 2-3 DWORDS, depending on the actual alignment.
  37
  38I'm pretty sure when no IR signal is present the receiver is always in a
  39marking state(1); but stray light, etc can cause intermittent noise values
  40as well.  Remember, this is a free running sample of the IR receiver state
  41over time, so don't assume any sample starts at any particular place.
  42
  43http://www.atmel.com/dyn/resources/prod_documents/doc2817.pdf
  44This data sheet (google search) seems to have a lovely description of the
  45RC5 basics
  46
  47http://www.nenya.be/beor/electronics/rc5.htm and more data
  48
  49http://www.ee.washington.edu/circuit_archive/text/ir_decode.txt
  50and even a reference to how to decode a bi-phase data stream.
  51
  52http://www.xs4all.nl/~sbp/knowledge/ir/rc5.htm
  53still more info
  54
  55
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