Level 1 Memory System
ARM DDI 0388I
Copyright © 2008-2012 ARM. All rights reserved.
7-12
ID073015
Non-Confidential
7.7
Parity error support
If your configuration implements parity error support, the features are as follows:
•
the parity scheme is even parity. For byte 0000000 parity is 0.
•
each RAM in the design generates parity information. As a general rule each RAM byte
generates one parity bit. Where RAM bit width is not a multiple of eight, the remaining
bits produce one parity bit.
There is also support for parity bit-writable data.
•
RAM arrays in a design with parity support store parity information alongside the data in
the RAM banks. As a result RAM arrays are wider when your design implements parity
support.
•
The Cortex-A9 logic includes the additional parity generation logic and the parity
checking logic.
shows the parity support design features and stages. In stages 1 and 2 RAM writes
and parity generation take place in parallel. RAM reads and parity checking take place in
parallel in stages 3 and 4.
Figure 7-2 Parity support
The output signals
PARITYFAIL[7:0]
report parity errors. Typically,
PARITYFAIL[7:0]
reports parity errors three clock cycles after the corresponding RAM read.
PARITYFAIL
is a
pulse signal that is asserted for one
CLK
clock cycle.
7.7.1
GHB and BTAC data corruption
The scheme provides parity error support for GHB RAMs and BTAC RAMs but this support
has limited diagnostic value. Corruption in GHB data or BTAC data does not generate
functional errors in the Cortex-A9 processor. Corruption in GHB data or BTAC data results in
a branch misprediction, that is detected and corrected.
DFF
RAM
arrays
Latch
DFF
DFF
RAM Read (addr)
RAM Read (data back)
Parity check (per byte) Parity values combined
DFF
DFF
RAM arrays
Cortex-A9
processor logic
Functional path (RAM read)
Parity path (parity check + error report)
1
Cortex-A9
processor logic
5
4
3
2
Parity path (parity generation)
Parity generation
Parity write (in WDATA)
Written Data select
RAM write
Functional path (RAM write)
PARITYFAIL[7:0]