AN2492 Freescale Semiconductor / Motorola, AN2492 Datasheet - Page 2

• Manufacturer Part Number: AN2492
• Description: MPC184 Descriptor Programmers Guide--PCI View
• Manufacturer: Freescale Semiconductor / Motorola

Data Packet Descriptor Overview
Data Packet Descriptor Overview
1 Data Packet Descriptor Overview
The MPC184 has bus mastering capability on either 32-bit PCI or the PowerQUICC 8xx bus to off-load data
movement and encryption operations from a host processor. As the system controller, the host processor
maintains a record of current secure sessions and the corresponding keys and contexts of those sessions.
Once the host has determined a security operation is required, it can either directly write keys, context, and
data to the MPC184 (MPC184 in target mode), or the host can create a ‘data packet descriptor’ to guide the
MPC184 through the security operation, with the MPC184 acting as a bus master. The descriptor can be
created in main memory, any memory local to the MPC184, including 8 Kbytes of on-chip gpRAM, or
written directly to the data packet descriptor buffer in the MPC184 crypto-channel.
2 Descriptor Structure
The MPC184 data packet descriptors are conceptually similar to descriptors used by most devices with
DMA capability. See Figure 1 for a conceptual data packet descriptor. The descriptors are fixed length
(64 bytes), and consist of sixteen 32-bit fields. Descriptors begin with a header, which describes the security
operation to be performed and the mode that the execution unit will be set to while performing the operation.
The header is followed by seven data length/data pointer pairs. Data length indicates the amount of
contiguous data to be transferred. This amount cannot exceed 32 Kbytes. The data pointer refers to the
address of the data which the MPC184 fetches. In this case, data is broadly interpreted to mean keys,
context, additional pointers, or the actual plain text to be permuted.
Figure 1 shows an example data packet descriptor.
2
31
MPC184 Descriptor Programmer’s Guide— PCI View
Freescale Semiconductor, Inc.
For More Information On This Product,
Figure 1. Example Data Packet Descriptor
Go to: www.freescale.com
Next Descriptor Pointer
Descriptor Header
Pointer 1
Pointer 2
Pointer 3
Pointer 4
Pointer 5
Pointer 6
Pointer 7
Length 2
Length 3
Length 4
Length 5
Length 6
Length 7
R/W
MOTOROLA
0