The Controller sends out System commands in the physical channel associated with the FRAMESYNC MediaLB frame alignment ChannelAddress (PC0). The NoData command indicates no command exists on the System Channel for this frame. All System commands are optional and may or may not be implemented on the MediaLB Controller. Additionally, System responses (including dynamic configuration) are optional and may or may not be implemented on a specific MediaLB Device.
The MOSTLock and MOSTUnlock commands indicate the status of the Controller relative to the MOST Network. When the Controller is not locked to the MOST Network (MOSTUnlock), all MediaLB data being transferred to or from the MOST Network must also stop. Buffers in the Controller could delay the stopping point to beyond when MOSTUnlock shows up on MediaLB.
The MLBReset command is designed to place the MediaLB interface in one or all Devices in a known state. When a MediaLB Device receives the MLBReset command, it will look at the corresponding first two received (most significant) data bytes on the MLBD line:
- If the first two bytes are zero, then all MediaLB Devices must reset their MediaLB interface to an initialized known state (broadcast reset to all Devices).
- If the first two bytes match the local DeviceAddress, then only the Device with the matching DeviceAddress will reset its MediaLB interface to an initialized known state (reset targeted to only one Device).
The MLBSubCmd command is used for configuration and status information from the Controller to Devices. A sub-command is contained in the first byte of the MLBD quadlet. When MediaLB Device interfaces receive the MLBSubCmd command, they will store the command and corresponding data quadlet (sub-command). Currently, only one sub-command is defined (scSetCA) and is used in dynamic configuration.
MediaLB Devices and ChannelAddresses can be configured using two methods: static or dynamic. When the EHC MediaLB Device uses the dynamic method, it instructs the Controller to scan for other MediaLB Devices. As Devices are found, the EHC then instructs the Controller to configure the found Device via the MLBSubCmd command.
The EHC determines which DeviceAddresses to scan for and, once a Device is found, which ChannelAddresses to assign. The EHC uses the pre-defined logical channels opened when MediaLB was started to transfer messages to the Controller. The EHC sends a message to the Controller to start scanning for a particular DeviceAddress. The Controller then sends the MLBScan command into the System Channel, and places the DeviceAddress into the first two bytes (most significant or first two transmitted) of the System Channel on MLBD.
An Rx Device with a matching DeviceAddress must send a status response of DevicePresent in the next System Channel if the ChannelAddresses are already assigned or fixed. If the ChannelAddresses have not been assigned, then the Rx Device must respond with DeviceServiceRequest.
If a Device is found, the Controller sends a message to the EHC indicating the Device’s presence and whether the Device needs to be configured or not. For Devices that need to be configured (requesting service), the EHC must then send a message to the Controller defining which ChannelAddresses to send to the Device. The Controller then sends this information to all Devices using the MLBSubCmd command in the System Channel.
The MLBSubCmd command data field contains four bytes that are defined as follows:
The scSetCA (01h) sub-command (under the MediaLB MLBSubCmd command) supports dynamic configuration of MediaLB ChannelAddresses. The bytes are defined as follows:
- scSetCA (01h) - Sub-command to Set ChannelAddress. Indicates that the rest of the bytes are logical channel configuration information.
- DA[8:1] - DeviceAddress bits 8 through 1, where all other bits are zero. Matches the DeviceAddress found during the MLBScan command.
- CA[8:1] - ChannelAddress bits 8 through 1, where all other bits are zero. Assigned ChannelAddress associated with a specific Index (Device’s logical channel) below.
- Index - Indicates which logical channel within a Device to associate the ChannelAddress with. This index enables a Device to support multiple logical channels. Index 0 and 1 are reserved for control channels. Devices that do not support control channels will start at Index 2 (with Indices 0 and 1 unused).
MediaLB Devices receiving this sub-command should check the DA[8:1] byte to determine whether this DeviceAddress matches its own. If the DeviceAddress matches, then the Device uses the ChannelAddress (CA[8:1] bits) for the logical channel associated with that Index. If a Device is reset or drops off MediaLB, it must reinitialize to its power-up state and discard any previously assigned ChannelAddresses.
MediaLB Device documentation must contain a table defining the relationship between the Index value, the particular logical channel associated with it, and the type and maximum bandwidth supported. In addition, the Device must indicate how many frames are needed to set the ChannelAddress once the scSetCA sub-command has been received. The EHC must use this data to determine the wait between setting Indices/Logical channels.