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Diffstat (limited to 'Documentation/networking/caif/Linux-CAIF.txt')
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diff --git a/Documentation/networking/caif/Linux-CAIF.txt b/Documentation/networking/caif/Linux-CAIF.txt deleted file mode 100644 index 0aa4bd381bec..000000000000 --- a/Documentation/networking/caif/Linux-CAIF.txt +++ /dev/null @@ -1,175 +0,0 @@ -Linux CAIF -=========== -copyright (C) ST-Ericsson AB 2010 -Author: Sjur Brendeland/ sjur.brandeland@stericsson.com -License terms: GNU General Public License (GPL) version 2 - - -Introduction ------------- -CAIF is a MUX protocol used by ST-Ericsson cellular modems for -communication between Modem and host. The host processes can open virtual AT -channels, initiate GPRS Data connections, Video channels and Utility Channels. -The Utility Channels are general purpose pipes between modem and host. - -ST-Ericsson modems support a number of transports between modem -and host. Currently, UART and Loopback are available for Linux. - - -Architecture: ------------- -The implementation of CAIF is divided into: -* CAIF Socket Layer and GPRS IP Interface. -* CAIF Core Protocol Implementation -* CAIF Link Layer, implemented as NET devices. - - - RTNL - ! - ! +------+ +------+ - ! +------+! +------+! - ! ! IP !! !Socket!! - +-------> !interf!+ ! API !+ <- CAIF Client APIs - ! +------+ +------! - ! ! ! - ! +-----------+ - ! ! - ! +------+ <- CAIF Core Protocol - ! ! CAIF ! - ! ! Core ! - ! +------+ - ! +----------!---------+ - ! ! ! ! - ! +------+ +-----+ +------+ - +--> ! HSI ! ! TTY ! ! USB ! <- Link Layer (Net Devices) - +------+ +-----+ +------+ - - - -I M P L E M E N T A T I O N -=========================== - - -CAIF Core Protocol Layer -========================================= - -CAIF Core layer implements the CAIF protocol as defined by ST-Ericsson. -It implements the CAIF protocol stack in a layered approach, where -each layer described in the specification is implemented as a separate layer. -The architecture is inspired by the design patterns "Protocol Layer" and -"Protocol Packet". - -== CAIF structure == -The Core CAIF implementation contains: - - Simple implementation of CAIF. - - Layered architecture (a la Streams), each layer in the CAIF - specification is implemented in a separate c-file. - - Clients must call configuration function to add PHY layer. - - Clients must implement CAIF layer to consume/produce - CAIF payload with receive and transmit functions. - - Clients must call configuration function to add and connect the - Client layer. - - When receiving / transmitting CAIF Packets (cfpkt), ownership is passed - to the called function (except for framing layers' receive function) - -Layered Architecture --------------------- -The CAIF protocol can be divided into two parts: Support functions and Protocol -Implementation. The support functions include: - - - CFPKT CAIF Packet. Implementation of CAIF Protocol Packet. The - CAIF Packet has functions for creating, destroying and adding content - and for adding/extracting header and trailers to protocol packets. - -The CAIF Protocol implementation contains: - - - CFCNFG CAIF Configuration layer. Configures the CAIF Protocol - Stack and provides a Client interface for adding Link-Layer and - Driver interfaces on top of the CAIF Stack. - - - CFCTRL CAIF Control layer. Encodes and Decodes control messages - such as enumeration and channel setup. Also matches request and - response messages. - - - CFSERVL General CAIF Service Layer functionality; handles flow - control and remote shutdown requests. - - - CFVEI CAIF VEI layer. Handles CAIF AT Channels on VEI (Virtual - External Interface). This layer encodes/decodes VEI frames. - - - CFDGML CAIF Datagram layer. Handles CAIF Datagram layer (IP - traffic), encodes/decodes Datagram frames. - - - CFMUX CAIF Mux layer. Handles multiplexing between multiple - physical bearers and multiple channels such as VEI, Datagram, etc. - The MUX keeps track of the existing CAIF Channels and - Physical Instances and selects the appropriate instance based - on Channel-Id and Physical-ID. - - - CFFRML CAIF Framing layer. Handles Framing i.e. Frame length - and frame checksum. - - - CFSERL CAIF Serial layer. Handles concatenation/split of frames - into CAIF Frames with correct length. - - - - +---------+ - | Config | - | CFCNFG | - +---------+ - ! - +---------+ +---------+ +---------+ - | AT | | Control | | Datagram| - | CFVEIL | | CFCTRL | | CFDGML | - +---------+ +---------+ +---------+ - \_____________!______________/ - ! - +---------+ - | MUX | - | | - +---------+ - _____!_____ - / \ - +---------+ +---------+ - | CFFRML | | CFFRML | - | Framing | | Framing | - +---------+ +---------+ - ! ! - +---------+ +---------+ - | | | Serial | - | | | CFSERL | - +---------+ +---------+ - - -In this layered approach the following "rules" apply. - - All layers embed the same structure "struct cflayer" - - A layer does not depend on any other layer's private data. - - Layers are stacked by setting the pointers - layer->up , layer->dn - - In order to send data upwards, each layer should do - layer->up->receive(layer->up, packet); - - In order to send data downwards, each layer should do - layer->dn->transmit(layer->dn, packet); - - -CAIF Socket and IP interface -=========================== - -The IP interface and CAIF socket API are implemented on top of the -CAIF Core protocol. The IP Interface and CAIF socket have an instance of -'struct cflayer', just like the CAIF Core protocol stack. -Net device and Socket implement the 'receive()' function defined by -'struct cflayer', just like the rest of the CAIF stack. In this way, transmit and -receive of packets is handled as by the rest of the layers: the 'dn->transmit()' -function is called in order to transmit data. - -Configuration of Link Layer ---------------------------- -The Link Layer is implemented as Linux network devices (struct net_device). -Payload handling and registration is done using standard Linux mechanisms. - -The CAIF Protocol relies on a loss-less link layer without implementing -retransmission. This implies that packet drops must not happen. -Therefore a flow-control mechanism is implemented where the physical -interface can initiate flow stop for all CAIF Channels. |