ST STM32F40 Series

Ethernet (ETH): media access control (MAC) with DMA controller RM0090
917/1422 Doc ID 018909 Rev 4
destination address, QTag prefix, length/type, LLC data and PAD (that is, all fields
except the preamble, SFD). The generating polynomial is the following:
The CRC value of a frame is computed as follows:
● The first 2 bits of the frame are complemented
● The n-bits of the frame are the coefficients of a polynomial M(x) of degree (n – 1). The
first bit of the destination address corresponds to the x
n – 1
term and the last bit of the
data field corresponds to the x
0
term
● M(x) is multiplied by x
32
and divided by G(x), producing a remainder R(x) of degree
≤ 31
● The coefficients of R(x) are considered as a 32-bit sequence
● The bit sequence is complemented and the result is the CRC
● The 32-bits of the CRC value are placed in the frame check sequence. The x
32
term is
the first transmitted, the x
0
term is the last one
Figure 331. MAC frame format
Gx() x
32
x
26
x
23
x
22
x
16
x
12
x
11
x
10
x
8
x
7
x
5
x
4
x
2
x1+ + + + + + + +++++++=
Preamble
SFD
Destination address
Source address
MAC client length/type
MAC client data
PAD
Frame check sequence
7 bytes
1 byte
6 bytes
6 bytes
2 bytes
46-1500 bytes
4 bytes
MSB LSB
Bit transmission order (right to left)
Bytes within
frame transmitted
top to bottom
ai15629