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