1 .. SPDX-License-Identifier: GPL-2.0
2
3 The Virtual PCM Test Driver
4 ===========================
5
6 The Virtual PCM Test Driver emulates a generic
7 testing/fuzzing of the userspace ALSA applicat
8 the PCM middle layer. Additionally, it can be
9 problems with PCM devices.
10
11 What can this driver do?
12 ~~~~~~~~~~~~~~~~~~~~~~~~
13
14 At this moment the driver can do the following
15 * Simulate both capture and playback p
16 * Generate random or pattern-based cap
17 * Inject delays into the playback and
18 * Inject errors during the PCM callbac
19
20 It supports up to 8 substreams and 4 channels.
21 non-interleaved access modes.
22
23 Also, this driver can check the playback strea
24 which is used in the corresponding selftest (a
25 layer data transferring functionality. Additio
26 RESET ioctl, and the selftest covers this PCM
27
28 Configuration
29 -------------
30
31 The driver has several parameters besides the
32
33 * fill_mode (bool) - Buffer fill mode
34 * inject_delay (int)
35 * inject_hwpars_err (bool)
36 * inject_prepare_err (bool)
37 * inject_trigger_err (bool)
38
39
40 Capture Data Generation
41 -----------------------
42
43 The driver has two modes of data generation: t
44 means random data generation, the second (1 in
45 data generation. Let's look at the second mode
46
47 First of all, you may want to specify the patt
48 by writing the pattern to the debugfs file. Th
49 for each channel, as well as entries which con
50
51 * /sys/kernel/debug/pcmtest/fill_patte
52 * /sys/kernel/debug/pcmtest/fill_patte
53
54 To set the pattern for the channel 0 you can e
55
56 .. code-block:: bash
57
58 echo -n mycoolpattern > /sys/kernel/de
59
60 Then, after every capture action performed on
61 channel 0 will contain 'mycoolpatternmycoolpat
62
63 The pattern itself can be up to 4096 bytes lon
64
65 Delay injection
66 ---------------
67
68 The driver has 'inject_delay' parameter, which
69 can be used for time delay/speedup simulations
70 it means the delay added between module's inte
71
72 If the 'inject_delay' value is positive, the b
73 negative - faster. You can try it yourself by
74 audiorecording application (like Audacity) and
75 source.
76
77 This parameter can be also used for generating
78 short period of time (with the negative 'injec
79
80 Errors injection
81 ----------------
82
83 This module can be used for injecting errors i
84 action can help you to figure out how the user
85 circumstances.
86
87 For example, you can make all 'hw_params' PCM
88 writing '1' to the 'inject_hwpars_err' module
89
90 .. code-block:: bash
91
92 echo 1 > /sys/module/snd_pcmtest/param
93
94 Errors can be injected into the following PCM
95
96 * hw_params (EBUSY)
97 * prepare (EINVAL)
98 * trigger (EINVAL)
99
100 Playback test
101 -------------
102
103 This driver can be also used for the playback
104 write the playback data to the 'pcmtest' PCM d
105 buffer for containing the looped pattern (whic
106 debugfs file for each channel). If the playbac
107 pattern, 'pc_test' debugfs entry is set into '
108
109 ioctl redefinition test
110 -----------------------
111
112 The driver redefines the 'reset' ioctl, which
113 this functionality, we can trigger the reset i
114 entry:
115
116 .. code-block:: bash
117
118 cat /sys/kernel/debug/pcmtest/ioctl_te
119
120 If the ioctl is triggered successfully, this f
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