AT32F421
Series Reference Manual
2022.11.11
Page 27
Rev 2.02
1.1 System overview
1.1.1
ARM Cortex
TM
-M4 processor
Cortex
®
-M4 processor is a low-power consumption processor featuring low gate count, low interrupt
latency, and low-cost debug. It supports DSP instruction set, particularly applicable to deep-embedded
applications that require quicker response to interrupts. Cortex
®
-M4 processor is based on ARMv7-M
architecture, supporting both Thumb instruction set and DSP instruction set.
shows the internal block diagram of Cortex
®
-M4 processor. Please refer to
ARM Cortex
®
-M4
Technical Reference Manual
for more information.
Figure 1-2 Internal block diagram of Cortex
®
-M4
NVIC
Cortex-M4 Core
MPU
FPB
DWT
AHB-AP
Bus Matrix
ITM
Cortex-M4
TPIU
SW-DP or
SWJ-DP
ROM Table
WIC
Interrupts and Power control
SW/JTAG
SBUS
DBUS
IBUS
1.1.2
Bit band
With the help of bit-band, read and write access to a single bit can be performed in the ordinary way of
loading and storing. The Cortex
®
-M4 memory includes two bit-band regions: the least significant 1M
bytes of SRAM and the least significant 1Mbytes of peripherals. In addition to access to bit-band
addresses, their respective bit-band alias region can be used to access to any bit in these two bit-band
regions. The bit-band alias region transforms each bit in it into a 32-bit word. Thus, accessing to an
address in an alias region has the same effect as read-modify-write operation on the targeted bit in a bit-
band region.
Figure 1-3 Comparison between bit-band region and its alias region: image A
0x2000_0000
0x2000_0004
0x2000_0008
0x2000_0000
0x200F_FFFC
Bit
0
8
16
24
31
0x2000_0000
0x2000_0010
0x2000_002C
0x2000_0080
bitband region address
(total 1M bytes)
bitband alias
region address