NXP Semiconductors MPC5644A, Reference Manual, Page: 826 / 1735

Enhanced Time Processing Unit (eTPU2)
MPC5644A Microcontroller Reference Manual, Rev. 6
826 Freescale Semiconductor
24.5.2.3.3 Parameter concurrency
Host accesses to parameters may occur in parallel with eTPU Microengine accesses. Readings taken from
a group of parameters while they are being simultaneously updated may lack coherency. eTPU provides
mechanisms to ensure parameter coherency in accesses from both Host side and Microengine side,
including the use of a coherent dual-parameter transfer mechanism, described in detail on
Section 24.5.4,
Parameter sharing and coherency .
24.5.2.3.4 Parameter sign extension area
The SPRAM address space to the Host is mirrored in a Parameter Sign Extension (PSE) area (see
Section 24.4.1, Memory map ). Accesses from the Host to the PSE area differ from accesses to the standard
SPRAM address space as follows:
• Writes : the most significant byte of the parameters is not written, and the SPRAM retains the old
byte value, regardless of the Host access size.
• Reads : the most significant bit of the 24-bit parameter (that is, the msbit of the second most
significant 32-bit parameter byte) is repeated in the 8 most significant bits of the read value on all
32-bit reads and most significant 16- and 8-bit reads.
The same parameters written in the standard SPRAM address space are read from the PSE area with the
same offsets, and vice-versa. See
Table 24-128 for a reference of the address offsets in big and little endian
machines.
This feature reliefs the Host from extending the signal of 24-bit eTPU parameters before calculations, and
from read-modify-write accesses to modify 24-bit parameters at the SPRAM.
24.5.2.4 SPRAM organization
The SPRAM internal partition for channel allocation is dynamic and programmed in the Channel Registers
(see
Section 24.4.7.1, ETPU_CxCR – eTPU Channel x Configuration Register ).
The Host application is responsible for allocating a different parameter base address to each channel during
the initial eTPU configuration, and to allocate enough parameters for the selected function, with no
unintentional overlapping between parameters of different functions.
Besides channel parameters, global areas may have to be allocated for parameters that are shared by more
than one channel, in one or both engines. Also, temporary parameter areas should be reserved to be used
by the coherent parameter transfer mechanisms described in
Section 24.5.4, Parameter sharing and
coherency , if necessary.