tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1.. SPDX-License-Identifier: GPL-2.0
2.. include:: <isonum.txt>
3
4
5================
6Using Linux CAIF
7================
8
9
10:Copyright: |copy| ST-Ericsson AB 2010
11
12:Author: Sjur Brendeland/ sjur.brandeland@stericsson.com
13
14Start
15=====
16
17If you have compiled CAIF for modules do::
18
19 $modprobe crc_ccitt
20 $modprobe caif
21 $modprobe caif_socket
22 $modprobe chnl_net
23
24
25Preparing the setup with a STE modem
26====================================
27
28If you are working on integration of CAIF you should make sure
29that the kernel is built with module support.
30
31There are some things that need to be tweaked to get the host TTY correctly
32set up to talk to the modem.
33Since the CAIF stack is running in the kernel and we want to use the existing
34TTY, we are installing our physical serial driver as a line discipline above
35the TTY device.
36
37To achieve this we need to install the N_CAIF ldisc from user space.
38The benefit is that we can hook up to any TTY.
39
40The use of Start-of-frame-extension (STX) must also be set as
41module parameter "ser_use_stx".
42
43Normally Frame Checksum is always used on UART, but this is also provided as a
44module parameter "ser_use_fcs".
45
46::
47
48 $ modprobe caif_serial ser_ttyname=/dev/ttyS0 ser_use_stx=yes
49 $ ifconfig caif_ttyS0 up
50
51PLEASE NOTE:
52 There is a limitation in Android shell.
53 It only accepts one argument to insmod/modprobe!
54
55Trouble shooting
56================
57
58There are debugfs parameters provided for serial communication.
59/sys/kernel/debug/caif_serial/<tty-name>/
60
61* ser_state: Prints the bit-mask status where
62
63 - 0x02 means SENDING, this is a transient state.
64 - 0x10 means FLOW_OFF_SENT, i.e. the previous frame has not been sent
65 and is blocking further send operation. Flow OFF has been propagated
66 to all CAIF Channels using this TTY.
67
68* tty_status: Prints the bit-mask tty status information
69
70 - 0x01 - tty->warned is on.
71 - 0x04 - tty->packed is on.
72 - 0x08 - tty->flow.tco_stopped is on.
73 - 0x10 - tty->hw_stopped is on.
74 - 0x20 - tty->flow.stopped is on.
75
76* last_tx_msg: Binary blob Prints the last transmitted frame.
77
78 This can be printed with::
79
80 $od --format=x1 /sys/kernel/debug/caif_serial/<tty>/last_rx_msg.
81
82 The first two tx messages sent look like this. Note: The initial
83 byte 02 is start of frame extension (STX) used for re-syncing
84 upon errors.
85
86 - Enumeration::
87
88 0000000 02 05 00 00 03 01 d2 02
89 | | | | | |
90 STX(1) | | | |
91 Length(2)| | |
92 Control Channel(1)
93 Command:Enumeration(1)
94 Link-ID(1)
95 Checksum(2)
96
97 - Channel Setup::
98
99 0000000 02 07 00 00 00 21 a1 00 48 df
100 | | | | | | | |
101 STX(1) | | | | | |
102 Length(2)| | | | |
103 Control Channel(1)
104 Command:Channel Setup(1)
105 Channel Type(1)
106 Priority and Link-ID(1)
107 Endpoint(1)
108 Checksum(2)
109
110* last_rx_msg: Prints the last transmitted frame.
111
112 The RX messages for LinkSetup look almost identical but they have the
113 bit 0x20 set in the command bit, and Channel Setup has added one byte
114 before Checksum containing Channel ID.
115
116 NOTE:
117 Several CAIF Messages might be concatenated. The maximum debug
118 buffer size is 128 bytes.
119
120Error Scenarios
121===============
122
123- last_tx_msg contains channel setup message and last_rx_msg is empty ->
124 The host seems to be able to send over the UART, at least the CAIF ldisc get
125 notified that sending is completed.
126
127- last_tx_msg contains enumeration message and last_rx_msg is empty ->
128 The host is not able to send the message from UART, the tty has not been
129 able to complete the transmit operation.
130
131- if /sys/kernel/debug/caif_serial/<tty>/tty_status is non-zero there
132 might be problems transmitting over UART.
133
134 E.g. host and modem wiring is not correct you will typically see
135 tty_status = 0x10 (hw_stopped) and ser_state = 0x10 (FLOW_OFF_SENT).
136
137 You will probably see the enumeration message in last_tx_message
138 and empty last_rx_message.