ADUC7025BCPZ32-RL7 AD [Analog Devices], ADUC7025BCPZ32-RL7 Datasheet - Page 46

• Manufacturer Part Number: ADUC7025BCPZ32-RL7
• Description: Precision Analog Microcontroller 12-bit Analog I/O, ARM7TDMI MCU
• Manufacturer: AD [Analog Devices]

ADuC7019/20/21/22/24/25/26/27
EXECUTION TIME FROM SRAM AND FLASH/EE
Execution from SRAM
Fetching instructions from SRAM takes one clock cycle as the
access time of the SRAM is 2 ns and a clock cycle is 22 ns
minimum. However, if the instruction involves reading or
writing data to memory, one extra cycle must be added if the
data is in SRAM (or three cycles if the data is in Flash/EE). One
cycle to execute the instruction, and two cycles to get the 32-bit
data from Flash/EE. A control flow instruction (a branch
instruction, for example) takes one cycle to fetch but also takes
two cycles to fill the pipeline with the new instructions.
Execution from Flash/EE
Because the Flash/EE width is 16 bits and access time for 16-bit
words is 22 ns, execution from Flash/EE cannot be done in
one cycle (as can be done from SRAM when CD Bit = 0). Also,
some dead times are needed before accessing data for any value
of CD bits.
In ARM mode, where instructions are 32 bits, two cycles are
needed to fetch any instruction when CD = 0. In thumb mode,
where instructions are 16 bits, one cycle is needed to fetch any
instruction.
Timing is identical in both modes when executing instructions
that involve using the Flash/EE for data memory. If the
instruction to be executed is a control flow instruction, an extra
cycle is needed to decode the new address of the program
counter and then four cycles are needed to fill the pipeline. A
data-processing instruction involving only the core register
does not require any extra clock cycle. However, if it involves
data in Flash/EE, an extra clock cycle is needed to decode the
address of the data, and two cycles are needed to get the 32-bit
data from Flash/EE. An extra cycle must also be added before
fetching another instruction. Data transfer instructions are
more complex and are summarized in Table 23.
Table 23. Execution Cycles in ARM/Thumb Mode
Instructions
LD
LDH
LDM/PUSH
STR
STRH
STRM/POP
1
2
The SWAP instruction combines an LD and STR instruction with only one
fetch, giving a total of eight cycles plus 40 μs.
N is the number of data to load or store in the multiple load/store instruction
(1 <N ≤ 16).
1
1
Fetch
Cycles
2/1
2/1
2/1
2/1
2/1
2/1
Dead
Time
1
1
N
1
1
N
2
1
Data Access
2
1
2 x N
2 x 20 μs
20 μs
2 x N x 20 μs
2
1
Dead
Time
1
1
N
1
1
N
1
1
Rev. A | Page 46 of 92
RESET AND REMAP
The ARM exception vectors are all situated at the bottom of the
memory array, from address 0x00000000 to address
0x00000020 as shown in Figure 50.
By default, and after any reset, the Flash/EE is mirrored at the
bottom of the memory array. The remap function allows the
programmer to mirror the SRAM at the bottom of the memory
array, which facilitates execution of exception routines from SRAM
instead of from Flash/EE. This means exceptions are executed twice
as fast, being executed in 32-bit ARM mode, and the SRAM being
32-bit wide instead of 16-bit wide Flash/EE memory.
Remap Operation
When a reset occurs on the ADuC7019/7020/7021/7022/
7024/7025/7026/7027, execution starts automatically in factory
programmed internal configuration code. This kernel is hidden
and cannot be accessed by user code. If the ADuC7019/7020/
7021/7022/7024/7025/7026/7027 are in normal mode (BM pin
is high), then they execute the power-on configuration routine
of the kernel and then jump to the reset vector address,
0x00000000, to execute the user’s reset exception routine.
Because the Flash/EE is mirrored at the bottom of the memory
array at reset, the reset interrupt routine must always be written
in Flash/EE.
The remap is done from Flash/EE by setting Bit 0 of the
REMAP register. Precaution must be taken to execute this
command from Flash/EE, above address 0x00080020, and not
from the bottom of the array as this is replaced by the SRAM.
This operation is reversible. The Flash/EE can be remapped at
address 0x00000000 by clearing Bit 0 of the REMAP MMR.
Precaution must again be taken to execute the remap function
from outside the mirrored area. Any type of reset remaps the
Flash/EE memory at the bottom of the array.
KERNEL
INTERRUPT
SERVICE ROUTINES
INTERRUPT
SERVICE ROUTINES
ARM EXCEPTION
VECTOR ADDRESSES
Figure 50. Remap for Exception Execution
0x00000020
0x00000000 0x00000000
0x00080000
0x00010000
0xFFFFFFFF
0x0008FFFF
0x00011FFF
FLASH/EE
SRAM
MIRROR SPACE