Embedded SRAM (eSRAM) Controllers
UG0331 User Guide Revision 15.0
191
6.2.2
Modes of Operation
There are two modes of operation for the eSRAM controller: SECDED-ON and SECDED-OFF.
6.2.2.1
SECDED-ON
SECDED mode can be turned ON by configuring the
register. The total available memory for
each eSRAM in this mode is 32 KB. The eSRAM controller generates 7 check bits for every 32 bits of
data, so for every 32 bits of data there will be 7 bits of encoded data. The 7 bits of ECC allow 1-bit
correction and 2-bit detection on the user data and ECC field. The 32 data bits and 7 bits of ECC are
written to the memory with zero wait states. Byte and half-word write operations are done using a
read-modify-write operation. The read-modify-write operation requires an additional wait state for byte
and half-word write operations.
In the case of a 1-bit error, the previous 32 bits of data and ECC value are read and correction takes
place automatically. The complete 32 bits plus ECC is rewritten. For byte and half-word write operations,
there is one wait state required as the ECC value is read and corrected for the byte/half-word.
When a 2-bit error is detected during a read cycle for 32-bit data, HRESP is asserted High for two clock
cycles and at the same time HREADYOUT goes Low for one clock cycle to indicate an error.
When a 2-bit error is detected during the read part of a read-modify-write byte or half-word operation,
HRESP is asserted High.
6.2.2.2
SECDED-OFF
SECDED mode can be turned OFF by configuring the
register. The total available memory for
each eSRAM is 40 KB. 1-bit correction and 2-bit detection on the user data is not applicable in this mode.
6.2.3
Pipeline Modes and Wait States for Read and Write Operations
When any master on the AHB bus matrix operates at a high frequency greater than 100 MHz, and is
accessing eSRAM, an extra clock cycle is needed for transactions. An optional pipeline can be enabled
on the Read data bus; this adds a clock cycle to all read operations. The pipeline is enabled by default in
both SECDED-ON and SECDED-OFF modes. When the master on the AHB bus matrix operates at low
frequency, less than 100 MHz, the pipeline can be turned off. Refer to
information on pipeline enable/ disable.
The actual frequency at which this is possible is specified in the AC characteristics table of
DS0451: IGLOO2 and SmartFusion2 Datasheet
. When the pipeline is disabled, the number of wait states
is less, increasing throughput of read operations.
2047
1FFD
5FFF
5FFE
5FFD
5FFC
1FFC
1FFF
1FFE
1FFD
1FFC
2048
0003
6003
6002
6001
6000
0002
2003
2002
2001
2000
2049
0007
6007
6006
6005
6004
0006
2007
2006
2005
2004
4094
1FFB
7FFB
7FFA
7FF9
7FF8
1FFA
3FFB
3FFA
3FF9
3FF8
4095
1FFF
7FFF
7FFE
7FFD
7FFC
1FFE
3FFF
3FFE
3FFD
3FFC
Table 120 •
SRAM Organization in SECDED-OFF Mode
(continued)