1 ===============================
2 Realtek PC Beep Hidden Register
3 ===============================
4
5 This file documents the "PC Beep Hidden Regist
6 Realtek HDA codecs and controls a muxer and pa
7 route audio between pins but aren't themselves
8 as I can tell, these hidden routes are designe
9 for codecs that don't have mixer widgets in th
10 to hide a mixer behind an undocumented vendor
11 as a widget, I have no idea.
12
13 Register Description
14 ====================
15
16 The register is accessed via processing coeffi
17 identified below have no discernible effect on
18
19 MSB LSB
20 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
21 | |h|S|L| | B |R| | Known bits
22 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
23 |0|0|1|1| 0x7 |0|0x0|1| 0x7 | Reset valu
24 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
25
26 1Ah input select (B): 2 bits
27 When zero, expose the PC Beep line (from the
28 enabled with the Set Beep Generation verb on
29 external PCBEEP pin) on the 1Ah pin node. Wh
30 jack (or possibly Line In on some machines)
31 selected, the 1Ah boost control has no effec
32
33 Amplify 1Ah loopback, left (L): 1 bit
34 Amplify the left channel of 1Ah before mixin
35 by h and S bits. Does not affect the level o
36
37 Amplify 1Ah loopback, right (R): 1 bit
38 Amplify the right channel of 1Ah before mixi
39 by h and S bits. Does not affect the level o
40
41 Loopback 1Ah to 21h [active low] (h): 1 bit
42 When zero, mix 1Ah (possibly with amplificat
43 into 21h (headphone jack on my machine). Mix
44 setting on 21h.
45
46 Loopback 1Ah to 14h (S): 1 bit
47 When one, mix 1Ah (possibly with amplificati
48 into 14h (internal speaker on my machine). M
49 setting on 14h and is present whenever 14h i
50
51 Path diagrams
52 =============
53
54 1Ah input selection (DIV is the PC Beep divide
55
56 <Beep generator> <PCBEEP pin> <Headphon
57 | | |
58 +--DIV--+--!DIV--+ {1Ah boost
59 | |
60 +--(b == 0)--+--(b != 0)--+
61 |
62 >1Ah (Beep/Headphone Mic/Line I
63
64 Loopback of 1Ah to 21h/14h::
65
66 <1Ah (Beep/Headphone Mic/Line I
67 |
68 {amplify if L/R}
69 |
70 +-----!h-----+-----S-----+
71 | |
72 {21h mute control} |
73 | |
74 >21h (Headphone)< >14h (Internal
75
76 Background
77 ==========
78
79 All Realtek HDA codecs have a vendor-defined w
80 provides access to a bank of registers that co
81 Registers are read and written via the standar
82 verbs (Set/Get Coefficient Index, Set/Get Proc
83 named "Realtek Vendor Registers" in public dat
84 apart from that, is entirely undocumented.
85
86 This particular register, exposed at coefficie
87 Realtek, is of note: unlike most registers, wh
88 amplifier parameters not in scope of the HDA s
89 routing which could just as easily have been d
90 and selector widgets.
91
92 Specifically, it selects between two sources f
93 ID (NID) 1Ah: the widget's signal can come eit
94 laptop, a Dell XPS 13 9350, it's the headphone
95 commits indicate that it might be a Line In on
96 Beep line (which is itself multiplexed between
97 generator and external PCBEEP pin, depending o
98 enabled via verbs on NID 01h). Additionally, i
99 amplification) that signal onto the 21h and/or
100
101 The register's reset value is 0x3717, correspo
102 then amplified and mixed into both the headpho
103 does this violate the HDA specification, which
104 beep input pin] connection may be maintained *
105 (**RST#**) is asserted", it means that we cann
106 about the input that 1Ah would otherwise expos
107 poorly shielded and picks up chassis noise (bo
108 machine).
109
110 Unfortunately, there are lots of ways to get t
111 Linux, it seems, has gone through most of them
112 after S3 suspend: judging by existing code, th
113 registers, and it's led to some fixes that imp
114 don't last after suspend. Other fixes have suc
115 away from PC Beep but have failed to disable b
116 machine, this means that the headphone input i
117 the headphone output, which uses the exact sam
118 causes terrible headphone noise, the character
119 1Ah boost control. (If you've seen instruction
120 noise by changing "Headphone Mic Boost" in ALS
121
122 The information here has been obtained through
123 the ALC256 codec's behavior and is not guarant
124 also applies for the ALC255, ALC257, ALC235, a
125 seem to be close relatives of the ALC256. (The
126 function.) Additionally, other codecs like the
127 register, judging by existing fixups in ``patc
128 data (e.g. node IDs, bit positions, pin mappin
129 from what I've described here.
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