MOTOROLA

MPC185 Security Processor Technical Summary

5

Each data packet descriptor contains the following:

•

Header—The header describes the required services and encodes information that indicates which

EUs to use and which modes to set.

•

Seven data length/data pointer pairs—The data length indicates the number of contiguous bytes of

data to be transferred. The data pointer indicates the starting address of the data, key, or context in

system memory.

•

Next descriptor pointer

A data packet descriptor ends with a pointer to the next data packet descriptor. Upon completion of the

current descriptor, this field is checked and, if non-zero, the channel is instructed to request a burst read of

the next descriptor.

Processing of the next descriptor (and whether or not a done signal is generated) is determined by the

programming of crypto-channel’s configuration register. Two modes of operation are supported:

•

Signal done at end of descriptor

•

Signal done at end of descriptor chain

The crypto-channel can signal done via an interrupt or by a write-back of the descriptor header after

processing a data packet descriptor. The value written back is identical to that of the header, with the

exception that a DONE field is set.

Occasionally, a descriptor field may not be applicable to the requested service. For example, if using DES

in ECB mode, the contents of the IV field do not affect the result of the DES computation. Therefore, when

processing data packet descriptors, the crypto-channel skips any pointer that has an associated length of

zero.

6.1 60x Interface

The 60x interface manages communication between the MPC185 internal execution units and the 60x bus.

The interface uses the 60x bus master/slave protocols. All on-chip resources are memory mapped, and the

target accesses and initiator writes from the MPC185 must be addressed on word boundaries. The MPC185

will perform initiator reads on byte boundaries and will adjust the data to place on word boundaries as

appropriate. Access to system memory is a critical factor in co-processor performance, and the native 60x

interface of the MPC185 allows it to achieve performance unattainable on secondary busses.

LEN_DATAOUT

PTR_DATAOUT

Length

Pointer

Number of bytes of data after ciphering

Pointer to location where cipher output is to be written

LEN_CTXOUT

PTR_CTXOUT

Length

Pointer

Length of output Context (IV)

Pointer to location where altered Context is to be written

Nul length

Nul pointer

Length

Pointer

Zeroes for fixed length descriptor filter

Zeroes for fixed length descriptor filter

Nul length

Nul pointer

Length

Pointer

Zeroes for fixed length descriptor filter

Zeroes for fixed length descriptor filter

PTR_NEXT

Pointer

Pointer to next data packet descriptor

Table 6-1. Example Data Packet Descriptor

Field Name

Value/Type

Description

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