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+ Section 1 Overview
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+
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+The Media Oriented Systems Transport (MOST) driver gives Linux applications
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+access a MOST network: The Automotive Information Backbone and the de-facto
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+standard for high-bandwidth automotive multimedia networking.
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+
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+MOST defines the protocol, hardware and software layers necessary to allow
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+for the efficient and low-cost transport of control, real-time and packet
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+data using a single medium (physical layer). Media currently in use are
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+fiber optics, unshielded twisted pair cables (UTP) and coax cables. MOST
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+also supports various speed grades up to 150 Mbps.
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+For more information on MOST, visit the MOST Cooperation website:
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+www.mostcooperation.com.
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+
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+Cars continue to evolve into sophisticated consumer electronics platforms,
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+increasing the demand for reliable and simple solutions to support audio,
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+video and data communications. MOST can be used to connect multiple
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+consumer devices via optical or electrical physical layers directly to one
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+another or in a network configuration. As a synchronous network, MOST
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+provides excellent Quality of Service and seamless connectivity for
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+audio/video streaming. Therefore, the driver perfectly fits to the mission
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+of Automotive Grade Linux to create open source software solutions for
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+automotive applications.
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+
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+The driver consists basically of three layers. The hardware layer, the
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+core layer and the application layer. The core layer consists of the core
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+module only. This module handles the communication flow through all three
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+layers, the configuration of the driver, the configuration interface
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+representation in sysfs, and the buffer management.
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+For each of the other two layers a selection of modules is provided. These
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+modules can arbitrarily be combined to meet the needs of the desired
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+system architecture. A module of the hardware layer is referred to as an
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+HDM (hardware dependent module). Each module of this layer handles exactly
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+one of the peripheral interfaces of a network interface controller (e.g.
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+USB, MediaLB, I2C). A module of the application layer is referred to as an
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+AIM (application interfacing module). The modules of this layer give access
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+to MOST via one the following ways: character devices, ALSA, Networking or
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+V4L2.
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+
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+To physically access MOST, an Intelligent Network Interface Controller
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+(INIC) is needed. For more information on available controllers visit:
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+www.microchip.com
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+
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+
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+
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+ Section 1.1 Hardware Layer
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+
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+The hardware layer contains so called hardware dependent modules (HDM). For each
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+peripheral interface the hardware supports the driver has a suitable module
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+that handles the interface.
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+
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+The HDMs encapsulate the peripheral interface specific knowledge of the driver
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+and provides an easy way of extending the number of supported interfaces.
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+Currently the following HDMs are available:
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+
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+ 1) MediaLB (DIM2)
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+ Host wants to communicate with hardware via MediaLB.
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+
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+ 2) I2C
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+ Host wants to communicate with the hardware via I2C.
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+
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+ 3) USB
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+ Host wants to communicate with the hardware via USB.
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+
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+
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+ Section 1.2 Core Layer
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+
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+The core layer contains the mostcore module only, which processes the driver
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+configuration via sysfs, buffer management and data forwarding.
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+
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+
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+
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+ Section 1.2 Application Layer
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+
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+The application layer contains so called application interfacing modules (AIM).
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+Depending on how the driver should interface to the application, one or more
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+suitable modules can be selected.
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+
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+The AIMs encapsulate the application interface specific knowledge of the driver
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+and provides access to user space or other kernel subsystems.
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+Currently the following AIMs are available
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+
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+ 1) Character Device
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+ Applications can access the driver by means of character devices.
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+
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+ 2) Networking
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+ Standard networking applications (e.g. iperf) can by used to access
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+ the driver via the networking subsystem.
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+
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+ 3) Video4Linux (v4l2)
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+ Standard video applications (e.g. VLC) can by used to access the
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+ driver via the V4L subsystem.
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+
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+ 4) Advanced Linux Sound Architecture (ALSA)
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+ Standard sound applications (e.g. aplay, arecord, audacity) can by
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+ used to access the driver via the ALSA subsystem.
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+
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+
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+
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+ Section 2 Configuration
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+
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+See ABI/sysfs-class-most.txt
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+
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+
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+
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+ Section 3 USB Padding
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+
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+When transceiving synchronous or isochronous data, the number of packets per USB
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+transaction and the sub-buffer size need to be configured. These values
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+are needed for the driver to process buffer padding, as expected by hardware,
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+which is for performance optimization purposes of the USB transmission.
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+
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+When transmitting synchronous data the allocated channel width needs to be
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+written to 'set_subbuffer_size'. Additionally, the number of MOST frames that
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+should travel to the host within one USB transaction need to be written to
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+'packets_per_xact'.
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+
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+Internally the synchronous threshold is calculated as follows:
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+
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+ frame_size = set_subbuffer_size * packets_per_xact
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+
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+In case 'packets_per_xact' is set to 0xFF the maximum number of packets,
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+allocated within one MOST frame, is calculated that fit into _one_ 512 byte
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+USB full packet.
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+
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+ frame_size = floor(MTU_USB / bandwidth_sync) * bandwidth_sync
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+
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+This frame_size is the number of synchronous data within an USB transaction,
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+which renders MTU_USB - frame_size bytes for padding.
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+
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+When transmitting isochronous AVP data the desired packet size needs to be
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+written to 'set_subbuffer_size' and hardware will always expect two isochronous
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+packets within one USB transaction. This renders
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+
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+ MTU_USB - (2 * set_subbuffer_size)
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+
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+bytes for padding.
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+
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+Note that at least 2 times set_subbuffer_size bytes for isochronous data or
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+set_subbuffer_size times packts_per_xact bytes for synchronous data need to be
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+put in the transmission buffer and passed to the driver.
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+
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+Since HDMs are allowed to change a chosen configuration to best fit its
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+constraints, it is recommended to always double check the configuration and read
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+back the previously written files.
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+
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+
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+
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+ Section 4 Routing Channels
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+
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+To connect a channel that has been configured as outlined above to an AIM and
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+make it accessible to user space applications, the attribute file 'add_link' is
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+used. To actually bind a channel to the AIM a string needs to be written to the
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+file that complies with the following syntax:
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+
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+ "most_device:channel_name:link_name[.param]"
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+
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+The example above links the channel "channel_name" of the device "most_device"
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+to the AIM. In case the AIM interfaces the VFS this would also create a device
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+node "link_name" in the /dev directory. The parameter "param" is an AIM dependent
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+string, which can be omitted in case the used AIM does not make any use of it.
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+
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+Cdev AIM example:
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+ $ echo "mdev0:ep_81:my_rx_channel" >add_link
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+ $ echo "mdev0:ep_81" >add_link
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+
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+
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+Sound/ALSA AIM example:
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+
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+The sound/ALSA AIM needs an additional parameter to determine the audio resolution
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+that is going to be used. The following strings can be used:
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+
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+ - "1x8" (Mono)
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+ - "2x16" (16-bit stereo)
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+ - "2x24" (24-bit stereo)
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+ - "2x32" (32-bit stereo)
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+
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+ $ echo "mdev0:ep_81:audio_rx.2x16" >add_link
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+ $ echo "mdev0:ep_81" >add_link
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Christian Gromm