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| -rw-r--r-- | Documentation/networking/caif/caif.rst | 139 |
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diff --git a/Documentation/networking/caif/caif.rst b/Documentation/networking/caif/caif.rst new file mode 100644 index 000000000..a07213030 --- /dev/null +++ b/Documentation/networking/caif/caif.rst @@ -0,0 +1,139 @@ +.. SPDX-License-Identifier: GPL-2.0 +.. include:: <isonum.txt> + + +================ +Using Linux CAIF +================ + + +:Copyright: |copy| ST-Ericsson AB 2010 + +:Author: Sjur Brendeland/ sjur.brandeland@stericsson.com + +Start +===== + +If you have compiled CAIF for modules do:: + + $modprobe crc_ccitt + $modprobe caif + $modprobe caif_socket + $modprobe chnl_net + + +Preparing the setup with a STE modem +==================================== + +If you are working on integration of CAIF you should make sure +that the kernel is built with module support. + +There are some things that need to be tweaked to get the host TTY correctly +set up to talk to the modem. +Since the CAIF stack is running in the kernel and we want to use the existing +TTY, we are installing our physical serial driver as a line discipline above +the TTY device. + +To achieve this we need to install the N_CAIF ldisc from user space. +The benefit is that we can hook up to any TTY. + +The use of Start-of-frame-extension (STX) must also be set as +module parameter "ser_use_stx". + +Normally Frame Checksum is always used on UART, but this is also provided as a +module parameter "ser_use_fcs". + +:: + + $ modprobe caif_serial ser_ttyname=/dev/ttyS0 ser_use_stx=yes + $ ifconfig caif_ttyS0 up + +PLEASE NOTE: + There is a limitation in Android shell. + It only accepts one argument to insmod/modprobe! + +Trouble shooting +================ + +There are debugfs parameters provided for serial communication. +/sys/kernel/debug/caif_serial/<tty-name>/ + +* ser_state: Prints the bit-mask status where + + - 0x02 means SENDING, this is a transient state. + - 0x10 means FLOW_OFF_SENT, i.e. the previous frame has not been sent + and is blocking further send operation. Flow OFF has been propagated + to all CAIF Channels using this TTY. + +* tty_status: Prints the bit-mask tty status information + + - 0x01 - tty->warned is on. + - 0x02 - tty->low_latency is on. + - 0x04 - tty->packed is on. + - 0x08 - tty->flow_stopped is on. + - 0x10 - tty->hw_stopped is on. + - 0x20 - tty->stopped is on. + +* last_tx_msg: Binary blob Prints the last transmitted frame. + + This can be printed with:: + + $od --format=x1 /sys/kernel/debug/caif_serial/<tty>/last_rx_msg. + + The first two tx messages sent look like this. Note: The initial + byte 02 is start of frame extension (STX) used for re-syncing + upon errors. + + - Enumeration:: + + 0000000 02 05 00 00 03 01 d2 02 + | | | | | | + STX(1) | | | | + Length(2)| | | + Control Channel(1) + Command:Enumeration(1) + Link-ID(1) + Checksum(2) + + - Channel Setup:: + + 0000000 02 07 00 00 00 21 a1 00 48 df + | | | | | | | | + STX(1) | | | | | | + Length(2)| | | | | + Control Channel(1) + Command:Channel Setup(1) + Channel Type(1) + Priority and Link-ID(1) + Endpoint(1) + Checksum(2) + +* last_rx_msg: Prints the last transmitted frame. + + The RX messages for LinkSetup look almost identical but they have the + bit 0x20 set in the command bit, and Channel Setup has added one byte + before Checksum containing Channel ID. + + NOTE: + Several CAIF Messages might be concatenated. The maximum debug + buffer size is 128 bytes. + +Error Scenarios +=============== + +- last_tx_msg contains channel setup message and last_rx_msg is empty -> + The host seems to be able to send over the UART, at least the CAIF ldisc get + notified that sending is completed. + +- last_tx_msg contains enumeration message and last_rx_msg is empty -> + The host is not able to send the message from UART, the tty has not been + able to complete the transmit operation. + +- if /sys/kernel/debug/caif_serial/<tty>/tty_status is non-zero there + might be problems transmitting over UART. + + E.g. host and modem wiring is not correct you will typically see + tty_status = 0x10 (hw_stopped) and ser_state = 0x10 (FLOW_OFF_SENT). + + You will probably see the enumeration message in last_tx_message + and empty last_rx_message. |