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MPC185 Security Processor Technical Summary

MOTOROLA

6.2 The MPC185 Controller

The MPC185 controller manages on-chip resources, including the individual execution units (EUs), FIFOs,

the 60x Interface, and the internal buses that connect all the various modules. The controller receives service

requests from the 60x interface and various crypto-channels, and schedules the required activities. The

controller can configure each of the on-chip resources in three modes:

•

Host-controlled mode—The host is directly responsible for all data movement into and out of the

resource.

•

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.

6.3 Host-Managed Register Access

All EUs can be used entirely through register read/write access. It is strongly recommended that read/write

access only be performed on a EU that is statically assigned to an idle crypto-channel. Such an assignment

is the only method for the host to inform the controller that a particular EU is in use.

6.4 Static EU Access

The controller can be configured to reserve one or more EUs to 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 MPC185 is supporting few (or one) contexts.

Static EU access can also be used to reserve one particular Public Key Execution Unit (PKEU) for one type

of computation. For example, one PKEU could be reserved for all private key RSA operations using prime

P, and the other could be reserved for all computations using prime Q. Again, this presents a performance

improvement because all fixed parameters can remain within the reserved PKEUs. This reduces the

overhead of loading and unloading contexts and therefore improves performance. However, this is only a

performance improvement if the lack of dynamically available PKEUs does not become a bottleneck in key

agreement protocols.

6.5 Dynamic EU Access

Processing begins when a data packet descriptor pointer is written to the Next Descriptor Pointer Register

of one of the crypto-channels. Prior to fetching the data referred to by the descriptor and based on the

services requested by the descriptor header in the descriptor buffer, 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 illegal access.

When dynamic assignment is used, each encryption/decryption packet must contain context that is

particular to the context being supported.

Freescale Semiconductor, Inc.

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