Freescale Semiconductor MCF5480 - Manual (Page 669)

EU Specific Data Packet Descriptors
MCF548x Reference Manual, Rev. 3
Freescale Semiconductor 22-67
Because the key and context are unchanging over multiple packets (or descriptors), the series of short reads
and writes required to set-up and tear down a session are avoided. This savings, along with the
crypto-channel having dedicated execution units, represents a noticeable performance improvement.
22.14 EU Specific Data Packet Descriptors
The following sections describe the data packet descriptor formats used with each of the SEC’s EUs. The
EU mode options (programmable via the PMODE and SMODE fields in the descriptor header) are also
covered.
22.14.1 AFEU Mode Options and Data Packet Descriptors
The AFEU implements an acceleration of a stream cipher compatible with RC4. There are several different
usage modes available.
Table 22-49 describes AFEU mode option fields.
PTR_1 Pointer (not used) NULL
LEN_2 IV Length NULL
PTR_2 IV Pointer NULL
LEN_3 Key Length NULL
PTR_3 Key Pointer NULL
LEN_4 Data In Length Number of bytes to be encrypted/decrypted
PTR_4 Data In Pointer Address of data to be encrypted/decrypted
LEN_5 Data Out Length Bytes to be written (should be equal to length of data in)
PTR_5 Data Out Pointer Address where final data is written
LEN_6 IV Out Length Number of bytes of IV to be written to memory (optional)
PTR_6 IV Out Pointer Address where IV is to be written
LEN_7 MAC Out Length NULL
PTR_7 MAC Out Pointer NULL
PTR_NEXT Next Descriptor Pointer Pointer to next data packet descriptor
7 6 5 4 3 2 1 0
Field — CS DC PP
Reset 0000_0000
Loc PEUMODE/SEUMODE Field in DPD Header
Figure 22-46. AFEU Mode Options
Table 22-48. Final Static Descriptor Example (Continued)
Field Name Value/Type Description