Descriptor Structure; Descriptor Format: Header Dword - Freescale Semiconductor MPC8313E Family Reference Manual

SEC channel. The channel uses this pointer to read the descriptor into its descriptor buffer. Once it obtains
the descriptor, the SEC uses its bus mastering capability to obtain inputs and write results, thus off-loading
data movement and encryption operations from the host processor.
For test purposes, it is also possible for the host to write keys, context, and text-data directly to execution
units, using the SEC's host-controlled access. This method avoids use of descriptors.
14.3.1

Descriptor Structure

SEC descriptors are conceptually similar to descriptors used by most devices with DMA capability. The
descriptors have a fixed length of 64 bytes, that is, eight long-words, consisting of one 'header dword' and
seven 'pointer dwords.' See
0
Header Dword
Pointer Dword 0 Length0
Pointer Dword 1 Length1
Pointer Dword 2 Length2
Pointer Dword 3 Length3
Pointer Dword 4 Length4
Pointer Dword 5 Length5
Pointer Dword 6 Length6
The header dword specifies the security operation to be performed, the execution unit(s) needed, and the
modes for each execution unit. The pointer dwords, all of which have the same format, contain pointer and
length information for locating input or output data parcels (such as keys, context, or text-data). The large
number of pointers provided in the descriptor allows for multi-algorithm operations that require fetching
of multiple keys, as well as fetch and return of contexts. Any pointer dword that is not needed can be given
a length of zero, and the channel will skip over the corresponding operations.
SEC descriptors include scatter/gather capability, which means that each pointer in a descriptor can be
either a direct pointer to a contiguous parcel of data, or can be a pointer to a link table, which is a list of
pointers and lengths used to assemble the data parcel. When a link table is used to read input data, this is
referred to as a 'gather' operation; when used to write output data, it is referred to as a 'scatter' operation.
14.3.2

Descriptor Format: Header Dword

Descriptors are created by the host to guide the SEC through required cryptographic operations. The
header dword defines the operations to be performed, the mode for each operation, and internal addressing
used by the controller and channel for internal data movement. The fields that must be supplied to the SEC
are shown in the 'Field' rows of
the host to create proper headers for each cryptographic operation.
MPC8313E PowerQUICC II Pro Integrated Processor Family Reference Manual, Rev. 3
Freescale Semiconductor
Figure 14-3 for the descriptor format.
15 16 17 23 24
Header
J0 Extent0
J1 Extent1
J2 Extent2
J3 Extent3
J4 Extent4
J5 Extent5
J6 Extent6
Figure 14-3. Descriptor Format
Figure 14-4, and described in
31 32
Reserved
—
—
—
—
—
—
—
Table 14-4. The SEC device drivers allow
Security Engine (SEC) 2.2
63
Pointer0
Pointer1
Pointer2
Pointer3
Pointer4
Pointer5
Pointer6
14-11