NXP Semiconductors MPC5566, Reference Manual

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Enhanced Time Processing Unit (eTPU)
MPC5566 Microcontroller Reference Manual, Rev. 2
18-6 Freescale Semiconductor
18.1.4.4 Shared Data Memory (SDM)
The SDM works as data RAM that can be accessed by the device core and up to two eTPU engines. This
memory is used for either:
• Information transfer between the device core and the eTPU
• Data storage for the eTPU microcode program
• Communication between the two eTPU engines
The SDM width is 32 bits, and is accessible by the host in any of the three formats: byte, 16-bit, or 32-bit.
The eTPU can access the SDM’s full 32 bits, lower 24 bits or upper byte (8-bit). The host can also access
the SDM space mirrored in an alternate area with parameter sign extension (PSE). PSE allows accessing
24-bit data as 32-bit sign-extended data without using the device’s bandwidth to extend the data.
Parameter sign extension accesses differ from the usual host accesses to the original SDM area:
Writes are effective only to the lower 3-bytes of a word: the word’s most significant byte (byte address) is
kept unaltered in SDM.
Figure 18-3. SDM PSE Area Write
NOTE
For the most significant byte, the word format is big endian.
Reads return the lower 3-bytes of a word sign-extended to 32 bits; the most significant bit of the word’s
second most significant byte (byte addresses) is copied in all 8 bits of the most significant read byte.
[31:24] [23:16] [15:8] [7:0]
Write 24-bit data
SDM
Most
byte significant
Lower three bytes