TC1784
Program Memory Unit (PMU)
User´s Manual
5-4
V1.1, 2011-05
PMU, V1.47
5.2
Overlay RAM and Data Acquisition
The overlay memory OVRAM is provided in the PMU0 especially for redirection of
program memory accesses to the OVRAM by using the data overlay function. The data
overlay functionality itself is controlled in the DMI module to avoid any performance
penalty during the execution of redirection, and to support also external memories.
For online data acquisition (OLDA) of application or calibration data a virtual 32 KB
memory range is provided which can be accessed without error reporting. Accesses to
this OLDA range can also be redirected to the overlay memory.
5.2.1
Internal Overlay Memory
The capacity of the OVRAM is 8 KB. The base address of the OVRAM is A/8FE8 0000
H
.
The internal Overlay Memory OVRAM is available in both, the production device and the
Emulation Device. Write accesses to the Overlay Memory OVRAM are possible in byte,
half-word, word and double-word widths. Read accesses are performed in 64-bit width.
Read-Modify-Write accesses are not supported.
As all other SRAMs in the device, also the OVRAM is ECC protected. The ECC
generation and detection is enabled in the OVRCON register. After enabling, the
OVRAM should be initialized by the user before any read access is performed. Also byte
or half-word write accesses to the OVRAM may result in ECC error detection (due to
read-modify-write) if the memory has not been initialized before the access
1)
. An ECC
error is reported to the SCU for control of error indication and of NMI trap (disabled after
reset).
5.2.2
Online Data Acquisition (OLDA)
Calibration is additionally supported by an OLDA memory range of up to 32 Kbyte, which
is a virtual memory and physically only available, if it is redirected (by user-controlled
overlay function) to the internal OVRAM, or in an Emulation Device to the Emulation
Memory EMEM or to the overlay region in external memory. Thus, if not redirected, write
accesses to the OLDA range are not really executed, and they do not generate a bus
error trap
2)
. Read accesses to the OLDA range in production devices generate a bus
error trap, if not redirected to a physically available overlay block. After redirection into
the OVRAM ECC errors may be reported also for byte/half-word/word write accesses
(see above).
1) Please note: the write of this read-modify-write sequence is always performed even if the read incurs a double-
bit error. So despite the reported error the written data and its ECC is correct after the sequence.
2) Attention: write accesses to the cached memory range will be executed by the TriCore by first reading this
address to fill the cache line before merging the new data in. The read will trigger the bus error trap in this
situation.
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