Freescale Semiconductor MCF5480 - Manual (Page 605)

Overview
MCF548x Reference Manual, Rev. 3
Freescale Semiconductor 22-3
22.4.2 SEC Controller Unit
The SEC controller unit manages on-chip resources, including the individual execution units (EUs),
FIFOs, the bus interface, and the internal buses that connect all the various modules. The controller
receives service requests from the bus interface and various crypto-channels, and schedules the required
activities. The controller can configure each of the on-chip resources in two modes:
• Static mode—The user can reserve a specific execution unit to a specific crypto-channel.
• Dynamic mode—A crypto channel can request a particular service from any available execution
unit.
22.4.2.1 Static EU Access
The controller can be configured to assign one or more EUs for a particular crypto-channel. Doing so
permits locking the EU to a particular context. When in this mode, the crypto-channel can be used by
multiple descriptors representing the same context without unloading and reloading the context at the end
of each descriptor. This mode presents considerable performance improvement over dynamic access, but
only when the SEC is supporting few (or one) contexts.
22.4.2.2 Dynamic EU Access
Processing begins when a data packet descriptor pointer is written to the fetch register (FR) of one of the
crypto-channels. First, the controller dynamically reserves usage of an EU to the crypto-channel. If all
appropriate EUs are already dynamically reserved by other crypto-channels, the crypto-channel stalls and
waits to fetch data until an appropriate EU is available. If multiple crypto-channels simultaneously request
the same EU, the EU is assigned on a weighted priority or round-robin basis.
Once the required EU has been reserved, the crypto-channel fetches and loads the appropriate data packets,
operates the EU, unloads data to system memory, and releases the EU for use by another crypto-channel.
If a crypto-channel attempts to reserve a statically-assigned EU (and no appropriate EUs are available for
dynamic assignment), an interrupt is generated and status indicates an illegal access. When dynamic
assignment is used, each encryption/decryption packet descriptor must contain the context and/or keys that
are required for the requested operation.
22.4.3 Crypto-Channels
The SEC includes two crypto-channels that manage data and EU function. Each crypto-channel consists
of the following:
• Control registers containing information about the transaction in process
• A status register containing an indication of the last unfulfilled bus request
• A pointer register indicating the location of a new descriptor to fetch
• Buffer memory used to store the active data packet descriptor
Crypto-channels analyze the data packet descriptor header and requests the first required cryptographic
service from the controller.
After the controller grants access to the required EU, the crypto-channel and the controller perform the
following steps:
1. Set the appropriate mode bits available in the EU for the required service.
2. Fetch context and other parameters as indicated in the data packet descriptor buffer and use these
to program the EU.
3. Fetch data as indicated and place in either the EU input FIFO or the EU itself (as appropriate).