NXP Semiconductors
UM10858
PN7462 family HW user manual
UM10858
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User manual
COMPANY PUBLIC
Rev. 1.4 — 14 May 2018
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283 of 345
Fig 66. Data-link layer frame format
Frame reception
The buffer manager extracts the frame length from the header. This gives the number of
bytes in the payload. It is compared with the length of a short frame as defined by the
field SHORT_FRAME_LEN in register HOSTIF_CONTROL_REG. If the frame length is
equal to or less than SHORT_FRAME_LEN, the buffer manager will try to find an
available RX buffer, which has been labelled as a “short frame buffer”. Otherwise it will
search for an available non-short RX buffer. The frame header is stored in the first word
of the selected RX buffer (with the number of padding bytes defined by
HOSTIF_BUFFER_RX<n>_CFG_REG.RX<n>_HEADER_OFFSET). The payload is
stored from the second word onwards. The CRC is extracted by the CRC checker for
verification; it is not stored in the RX buffer.
Frame
transmission
The buffer manager reads the first word from the TX buffer and removes the
m
most
significant bytes (where m = HOSTIF_BUFFER_TX_CFG_REG.TX_HEADER_OFFSET)
to get the header, from which it extracts the frame length. It then reads out the number of
bytes corresponding to this frame length. Once the payload has been read out, the CRC
Generator appends the CRC to the end of the TX frame.
14.3.4.3 Native format
The Native frame format has neither a header nor a CRC: it is a free-format payload.
Frame reception
The payload is stored from the second word of the RX buffer onwards. When the buffer
manager sees that EOF
is asserted, it writes the number of received bytes into the first
word of the buffer. The format to write this number of bytes is similar to HDLL header
with offset 0: byte at address 0 is Counter MSB (3 bits), byte at address 1 is Counter LSB
(8 bits). 16 MSB of 1st word are 0.
Frame transmission
