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- Copyright (C) ST-Ericsson AB 2010
- Author: Sjur Brendeland/ sjur.brandeland@stericsson.com
- License terms: GNU General Public License (GPL) version 2
- ---------------------------------------------------------
- === 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.
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