MuditaOS/module-cellular/modem

Cellular Multiplexer

Table of contents

1. Modes
2. Single command data flow
3. Cellular result structures
4. Error codes

Modes

Cellular operates in three modes:

• AT,
• CMUX setup,
• CMUX

The AT mode is used for communication setup and modem configuration.

The CMUX setup is an intermidiate state starting a CMUX communication:

• It configures CMUX mode's transmission parameters.
• It creates channels for a frame multiplexing (Commands, Notifications, Data). Data flow for both CMUX and CMUX setup in current implementation is identical.

For more details, see channel implementation.

Single command data flow

A single command sequence starts with a call from the Service and can end in one of three ways:

• Command response timeout (timeout depends on command issued).
• Service receives an error in result and handles it accordingly.
• Command response is successfully parsed before timeout and passed to service layer.

Result structs

Currently, there are two types of structs used to pass data between contexts.

DMA result struct is used to directly store data from DMA engine as well as pass these through MessageBuffer to Worker. This struct has static data buffer maximum size.

Cellular Result is used to pass complete frames serialized in vector together with result code. This struct has variable size.

Error codes

Currently there are different errors/results codes for different layers.

1. CellularResultCode This code is used to pass information from bsp layer up to channel. It can be either used to handle flow control messages from DMA or to pass failures to upper layer (transmission/receiving not starter, cmux frame error).

   Uninitialized,
   ReceivedAndIdle,
   ReceivedAndFull,
   ReceivedAfterFull,
   ReceivedNoData,
   ReceivingNotStarted,
   TransmittingNotStarted,
   CMUXFrameError, 
   

2. AtResult This result code is passed to service layer.

   OK,              /// at OK
   ERROR,           /// at ERROR For compatibility also for CME_ERROR and CMS_ERROR (details in errorCode)
   CME_ERROR,       /// In case CME error see errorCode
   CMS_ERROR,       /// In case CMS error see errorCode
   TIMEOUT,         /// at Timeout
   TOKENS,          /// at numbers of tokens needed met
   NONE,            /// no code
   UNDEFINED,       /// undefined result - usage of Undefined result, define and pin result to use it
   PARSING_ERROR,   /// parser error
   FULL_MSG_BUFFER, /// at not enough space left in message buffer for new message
   TRANSMISSION_NOT_STARTED, /// at dma not starting transmission
   RECEIVING_NOT_STARTED,    /// at dma not starting requested receiving
   DATA_NOT_USED,            /// at received data not being used
   CMUX_FRAME_ERROR,         /// at cmux deserialize error