Crc Calculation Unit; Crc Introduction; Crc Main Features; Crc Functional Description - ST STM32F40 Series Reference Manual

RM0090
4

CRC calculation unit

This section applies to the whole STM32F4xx family, unless otherwise specified.
4.1

CRC introduction

The CRC (cyclic redundancy check) calculation unit is used to get a CRC code from a 32-bit
data word and a fixed generator polynomial.
Among other applications, CRC-based techniques are used to verify data transmission or
storage integrity. In the scope of the EN/IEC 60335-1 standard, they offer a means of
verifying the Flash memory integrity. The CRC calculation unit helps compute a signature of
the software during runtime, to be compared with a reference signature generated at link-
time and stored at a given memory location.
4.2

CRC main features

●
Uses CRC-32 (Ethernet) polynomial: 0x4C11DB7
–
●
Single input/output 32-bit data register
● CRC computation done in 4 AHB clock cycles (HCLK)
●
General-purpose 8-bit register (can be used for temporary storage)
The block diagram is shown in
Figure 6.
4.3

CRC functional description

The CRC calculation unit mainly consists of a single 32-bit data register, which:
●
is used as an input register to enter new data in the CRC calculator (when writing into
the register)
●
holds the result of the previous CRC calculation (when reading the register)
32 26 23 22
X + X + X + X
Figure
CRC calculation unit block diagram
CRC computation (polynomial: 0x4C11DB7)
32-bit (write access)
Doc ID 018909 Rev 4
16 12 11
+ X + X + X + X
6.
AHB bus
Data register (output)
Data register (input)
CRC calculation unit
10 8 7 5 4
+X + X + X + X
32-bit (read access)
2
+ X + X +1
ai14968
86/1422