SAM7S256_14 Datasheet, PDF (107/775 Pages) ATMEL Corporation – ARM-based Flash MCU

19.2.2 Read Operations
An optimized controller manages embedded Flash reads. A system of 2 x 32-bit buffers is added in order to start
access at following address during the second read, thus increasing performance when the processor is running in
Thumb mode (16-bit instruction set). See Figure 19-2, Figure 19-3 and Figure 19-4.
This optimization concerns only Code Fetch and not Data.
The read operations can be performed with or without wait state. Up to 3 wait states can be programmed in the
field FWS (Flash Wait State) in the Flash Mode Register MC_FMR (see “MC Flash Mode Register” on page 115).
Defining FWS to be 0 enables the single-cycle access of the embedded Flash.
The Flash memory is accessible through 8-, 16- and 32-bit reads.
As the Flash block size is smaller than the address space reserved for the internal memory area, the embedded
Flash wraps around the address space and appears to be repeated within it.
Figure 19-2. Code Read Optimization in Thumb Mode for FWS = 0
Master Clock
ARM Request (16-bit)
Code Fetch
@Byte 0
@Byte 2 @Byte 4
Flash Access
Bytes 0-3 Bytes 4-7
@Byte 6 @Byte 8
@Byte 10 @Byte 12
@Byte 14 @Byte 16
Bytes 8-11
Bytes 12-15
Bytes 16-19
Buffer (32 bits)
Bytes 0-3
Bytes 4-7
Bytes 8-11
Bytes 12-15
Data To ARM
Bytes 0-1 Bytes 2-3 Bytes 4-5 Bytes 6-7 Bytes 8-9 Bytes 10-11 Bytes 12-13 Bytes 14-15
Note: When FWS is equal to 0, all accesses are performed in a single-cycle access.
Figure 19-3. Code Read Optimization in Thumb Mode for FWS = 1
1 Wait State Cycle
1 Wait State Cycle
1 Wait State Cycle
1 Wait State Cycle
Master Clock
ARM Request (16-bit)
Code Fetch
@Byte 0
Flash Access
@Byte 2
Bytes 0-3
@Byte 4 @Byte 6
@Byte 8 @Byte 10
@Byte 12 @Byte 14
Bytes 4-7
Bytes 8-11
Bytes 12-15
Buffer (32 bits)
Bytes 0-3
Bytes 4-7
Bytes 8-11
Data To ARM
Bytes 0-1 Bytes 2-3 Bytes 4-5 Bytes 6-7 Bytes 8-9 Bytes 10-11 Bytes 12-13
Note: When FWS is equal to 1, in case of sequential reads, all the accesses are performed in a single-cycle access (except for the
first one).
SAM7S Series [DATASHEET]
6175M–ATARM–26-Oct-12
107