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Documentation / video4linux / hauppauge-wintv-cx88-ir.txt




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Based on kernel version 3.16. Page generated on 2014-08-06 21:41 EST.

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