1 .. SPDX-License-Identifier: GPL-2.0
2
3 =============================================
4 Linux Kernel GPIO based sloppy logic analyzer
5 =============================================
6
7 :Author: Wolfram Sang
8
9 Introduction
10 ============
11
12 This document briefly describes how to run the
13 logic analyzer running on an isolated CPU.
14
15 The sloppy logic analyzer will utilize a few G
16 system to rapidly sample these digital lines,
17 criteria is met, result in a time series log w
18 appeared on these lines. One way to use it is
19 connected to these GPIO lines with wires (i.e.
20 common logic analyzer.
21
22 Another feature is to snoop on on-chip periphe
23 peripherals can be used in GPIO input mode at
24 used as inputs or outputs for the peripheral.
25 I2C traffic without any wiring (if your hardwa
26 control subsystem such pin controllers are cal
27 can be used with a certain peripheral and as a
28 time.
29
30 Note that this is a last resort analyzer which
31 non-deterministic code paths and non-maskable
32 for a reason. However, for e.g. remote develop
33 first view and aid further debugging.
34
35 Setup
36 =====
37
38 Your kernel must have CONFIG_DEBUG_FS and CONF
39 runtime environment does not utilize cpusets o
40 core is easiest. If you do need cpusets, check
41 sloppy logic analyzer does not interfere with
42
43 Tell the kernel which GPIOs are used as probes
44 you need to use the following bindings. Becaus
45 debugging, there is no official schema::
46
47 i2c-analyzer {
48 compatible = "gpio-sloppy-logic-an
49 probe-gpios = <&gpio6 21 GPIO_OPEN
50 probe-names = "SCL", "SDA";
51 };
52
53 Note that you must provide a name for every GP
54 maximum of 8 probes are supported. 32 are like
55 implemented yet.
56
57 Usage
58 =====
59
60 The logic analyzer is configurable via files i
61 strongly recommended to not use them directly,
62 ``tools/gpio/gpio-sloppy-logic-analyzer``. Bes
63 extensively, it will isolate the CPU core so y
64 disturbance while measuring.
65
66 The script has a help option explaining the pa
67 snippet which analyzes an I2C bus at 400kHz on
68 following settings are used: The isolated CPU
69 core in a big.LITTLE setup. Because CPU1 is th
70 parameter. The bus speed is 400kHz. So, the sa
71 sample at least at 800kHz. However, falling ed
72 start condition happen faster, so we need a hi
73 ``-s 1500000`` for 1.5MHz. Also, we don't want
74 for a start condition on an idle bus. So, we n
75 edge on SDA while SCL stays high, i.e. ``-t 1H
76 us assume 15ms here which results in the param
77 altogether::
78
79 gpio-sloppy-logic-analyzer -s 1500000 -t 1
80
81 Note that the process will return you back to
82 still sampling in the background. Unless this
83 result file in the current or specified direct
84 will then need to trigger I2C communication::
85
86 i2cdetect -y -r <your bus number>
87
88 Result is a .sr file to be consumed with Pulse
89 `sigrok`_ project. It is a zip file which also
90 which may be consumed by other software. The f
91 instance name plus a since-epoch timestamp.
92
93 .. _sigrok: https://sigrok.org/
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