Copyright © Siemens AG 2016. All rights reserved
29
ERTEC 200P-2 Manual
Technical data subject to change
Version 1.0
After ARM926-TCM reset, the I/D-TCM is automatically initialized by the HW. The initiali-
zation process (incl. EDC bits) for the complete I/D-TCM takes ca. 16.5 µs. The end of
the initialization process is signaled in the SCRB register 'EDC_INIT_DONE' (see
2.3.10.9.22
X
) (I_TCM926_INIT_DONE, D_TCM926_INIT_DONE). The EDC logic can also
be disabled using the SCRB register 'EDC_PARITY_EN' (see 2.3.10.9.22
). The
'EDC_DISABLE_ARM926' bit deactivates the EDC logic. The EDC logic is enabled after
reset.
The D-TCM can be written and read by the AHB masters (PN-IP, host interface and
GDMA). Access to the D-TCM by one of these masters stalls the ARM (pipeline paused).
Per word of transfer, this stall usually only lasts for one processor clock cycle to allow
transfer from the 'DMA-DTCM Access Controller' (part of the ARM926 subsystem) to the
D-TCM or vice versa. Arbitration is round robin, i.e. access to the D-TCM is executed
time about by ARM and the 'DMA-DTCM Access Controller'. Arbitration is also carried
again after each individual instance of access for burst transfer.
Table 1 lists the various types of ARM926EJ-S access to I/D-TCM and the AHB and the
potential errors:
Table 1: Types of ARM926EJ-S access to I/D-TCM / AHB
2.3.1.3.3 Memory Management Unit (MMU)
The MMU (see ARM926EJ-S Technical Reference Manual /7/ ) supports a demand page
virtual memory system which may be required by operating systems such as Linux and
ECOS depending on the application. The MMU contains the access protection mecha-
nisms for all memory access. Address translation, access protection and region type are
saved in one TLB (Translation Lookaside Buffer). Separate TLBs are available for instruc-
tion and data. These TLBs are automatically evaluated and updated by the MMU hard-
ware.
Page size: 1 MByte, 64 KByte, 4 KByte and 1 KByte
Separate TLBs for instruction and data
Access attributes can be changed without a TLB flush
A fast context switch enables virtual address remapping in a 0 – 32 MByte area
TLB entries can be locked
The MMU RAMs are
not assigned parity
.
EAS 926 , 250 MHz
Description:
Memory area
AHB write
access
AHB read
access
AHB read getting
an ECC detect
AHB read getting
an ECC error
TCM write
access
TCM read
access
TCM read
ECC detect
TCM read
ECC error
ok
no error
ITCM area
(from AHB not possible)
na1
na1
na1
na1
ok
ok
I-TCM926-1B
I-TCM926-1B
+
I-TCM926-2B
na1
not availiable /
access is not possible
ITCM area hole
(from AHB not possible)
na1
na1
na1
na1
Invalid I-
TCM926
Access
Invalid I-
TCM926
Access
na2
na2
na2
not availiable /
access never issues an
ECC detect/error
ITCM area mirror
(not possible)
na1
na1
na1
na1
na1
na1
na1
na1
AHB error
AHB error response
via HRESP
D-TCM926-1B
AHB ECC detect signal
DTCM area
ok
ok
D-TCM926-1B
D-TCM926-1B
+
D-TCM926-2B
ok
ok
D-TCM926-1B
D-TCM926-1B
+
D-TCM926-2B
D-TCM926-2B
AHB ECC error signal
8ns width for the DTCM
DTCM area hole
(from AHB not possible)
na1
na1
na1
na1
Invalid D-
TCM926
Access
Invalid D-
TCM926
Access
na2
na2
I-TCM926-1B
AHB ECC detect signal
8ns width for the ITCM
DTCM area mirror
(not possible)
na1
na1
na1
na1
na1
na1
na1
na1
I-TCM926-2B
AHB ECC error signal
8ns width for the ITCM
access types
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