It has been the subject of several standards. IEC is a technical international standard for letter symbols published by the International Electrotechnical Commission, comprising the following parts: mLAN, short for Music Local Area Network, is a transport level protocol for synchronized transmission and management of multi-channel digital audio, video, control signals and multi-port MIDI over a network. In electrical engineering and power system automation, the International Electrotechnical Commission standards define systems used for telecontrol. Such systems are used for controlling electric power transmission grids and other geographically widespread control systems.
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An iec compliant driver exports two device nodes for isochronous and for asynchronous transactions. The data buffer is mapped into a user process address space, which means no data copying between the kernel and an application is necessary. Synchronization between user processes and the driver is performed using ioctl 2 commands.
Then the data buffer can be mapped into the process space using mmap 2. A circular data buffer consists of one or more equal size frame buffers further referred to as frames, unless to avoid ambiguity with AV frames. Frames are numbered starting with zero and are always transferred sequentially. Frames consist equal sized packets. Each packet contains a CIP header and one or more data blocks.
A driver and an application act as a producer and a consumer: producer supplies full frames filled with data to the consumer, and the producer is not allowed to access those frames until the consumer claims them empty. Bus-specific overhead, such as isochronous packet headers, is handled by the driver and is not exposed to applications.
Data returned by read 2 contains CIP headers and data blocks. Empty packets are not returned by read 2. If no channels were allocated, the driver uses the broadcast channel by default and allocates the default-size data buffer. If it is one of the formats supported by the driver, it is properly transmitted with inserted empty packets and timestamps.
For both methods, if during transmit the driver runs out of data, it transmits empty packets containing only a CIP header of the next to be transmitted packet, as defined in IEC Asynchronous Transactions read 2 , write 2 , ioctl 2 , and poll 2 can be used with asynchronous nodes. Outgoing frames are sent using write 2 , incoming frames are received with read 2. Reading an ARQ takes one or two steps depending on data length.
If there were established isochronous connections before bus reset, the driver attempts to restore all connections as described in IEC and resume any active transfers that were in progress.
IEC-61883 Client Drivers