.. _SM_AT_CMUX: CMUX AT commands **************** .. contents:: :local: :depth: 2 This page describes CMUX-related AT commands. The GSM 0710 multiplexer protocol (CMUX) enables multiplexing multiple data streams through a single serial link, setting up one channel per data stream. For example, it can be used to exchange AT data and have a :ref:`Point-to-Point Protocol (PPP) ` link up at the same time on a single UART. |SM| implements the basic option of the CMUX protocol with only UIH frames as described in the `3GPP TS 27.010`_ specification. The maximum length of the information field in UIH frames is configurable using the ``CONFIG_MODEM_CMUX_MTU`` Kconfig option, which defaults to 127 bytes. .. note:: To use the nRF91 Series SiP as a cellular dial-up PPP modem, see :ref:`sm_cellular_modem`. CMUX is enabled in |SM| by compiling it with the appropriate configuration files, depending on your use case. See the :ref:`sm_config_files` section for more information. .. note:: * Only basic mode (mode 0) is supported. * Only UIH frames are used. * The speed used is the configured baud rate of |SM|'s UART. * No system parameters (N1, T1, T2, T3, k, m) are configurable. CMUX setup +CMUX ================ The ``AT+CMUX`` command starts the CMUX multiplexer. It is defined in `3GPP TS 27.007`_ (section 5.7) and the underlying protocol is specified in `3GPP TS 27.010`_. Only basic mode (``=0``) with subset ``0`` is supported. All other parameter values are rejected. Set command ----------- The set command allows you to start the CMUX multiplexer. An ``OK`` response is sent before CMUX is started, after which only CMUX framing is accepted on the serial link. Syntax ~~~~~~ :: AT+CMUX=[,] * The ```` parameter selects the operation mode. Only ``0`` (basic mode) is supported. * The ```` parameter selects the subset of mode 0. Only ``0`` is supported. Default value is ``0``. Read command ------------ The read command returns the current multiplexer configuration. Syntax ~~~~~~ :: AT+CMUX? Response syntax ~~~~~~~~~~~~~~~ :: +CMUX: , * The ```` parameter is always ``0`` (basic mode). * The ```` parameter is always ``0``. Test command ------------ The test command returns the supported parameter ranges. Syntax ~~~~~~ :: AT+CMUX=? Response syntax ~~~~~~~~~~~~~~~ :: +CMUX: (0),(0) Example ------- :: AT+CMUX=? +CMUX: (0),(0) OK AT+CMUX? +CMUX: 0,0 OK AT+CMUX=0 OK // CMUX is now started. Open the CMUX channels to continue communication. AT+CMUX=0,0 OK // Equivalent to AT+CMUX=0. CMUX setup #XCMUX ================= .. note:: ``AT#XCMUX`` is a compatibility command for Serial Modem v1.x.x and is not recommended for new designs. Use the standard ``AT+CMUX=0`` command instead. The ``#XCMUX`` command manages the configuration of CMUX over the serial link. Set command ----------- The set command allows you to start CMUX and assign the CMUX channels. The CMUX link is closed down automatically when the remote end sends the CMUX Multiplexer Close Down (CLD) sequence. The CMUX link can be closed manually with the ``AT#XCMUXCLD`` command. Syntax ~~~~~~ :: AT#XCMUX[=] The ```` parameter is an integer used to indicate the address of the AT channel. The AT channel denotes the CMUX channel where AT data (commands, responses, notifications) is exchanged. If specified, it must be ``1``, unless :ref:`PPP ` is enabled. If PPP is enabled, it can also be ``2`` (to allocate the first CMUX channel to PPP). If not specified, the previously used address is used. If no address has been previously specified, the default address is ``1``. .. note:: If there is more than one CMUX channel (such as when using :ref:`PPP `), the non-AT channels will automatically get assigned to addresses other than the one used for the AT channel. For example, if PPP is enabled and CMUX is started with the ``AT#XCMUX=2`` command, the AT channel will be assigned to address ``2`` and the PPP channel to address ``1``. An ``OK`` response is sent if the command is accepted, after which CMUX is started. This means that after successfully running this command, you must set up the CMUX link and open the channels appropriately. The AT channel will be available at the configured address. You can send an empty ``AT`` command to make sure that the protocol is set up properly. .. caution:: Using ``AT#XCMUX`` to switch the AT command channel at runtime is error-prone and not recommended. The channel switching might run out of sync with automatic PPP startup and recovery enabled by ``AT#XPPP=1``. Read command ------------ The read command allows you to read the address of the AT channel and the total number of channels. Syntax ~~~~~~ :: AT#XCMUX? Response syntax ~~~~~~~~~~~~~~~ :: #XCMUX: , * The ```` parameter indicates the address of the AT channel. It is between ``1`` and ````. * The ```` parameter is the total number of CMUX channels. It depends on what features are enabled (for example, :ref:`PPP `). Example ------- Without PPP: :: AT#XCMUX? #XCMUX: 1,1 OK AT#XCMUX OK // Here, CMUX is started and communication can now happen only through it (until a reset). // Open the AT channel, which is the only one, to continue exchanging AT data. AT OK With PPP: :: AT#XCMUX? #XCMUX: 1,2 OK AT#XCMUX=2 OK // Start up CMUX and open the channels. The AT channel is now at address 2. AT#XCMUX? #XCMUX: 2,2 OK CMUX close down #XCMUXCLD ========================= The ``#XCMUXCLD`` command closes down the CMUX service. This command can be used on host devices that do not support sending the CMUX Multiplexer close-down sequence. Once CMUX is closed down, the serial link returns to AT command mode. Set command ----------- The set command allows you to close down the CMUX link. Syntax ~~~~~~ :: AT#XCMUXCLD An ``OK`` response is sent in the CMUX channel if the command is accepted, after which CMUX is closed down. Read command ------------ The read command is not supported.