Table 390. Rx Fifo Element; Table 391. Rx Fifo Element Description - ST STM32G4 Series Reference Manual

FD controller area network (FDCAN)
Due to the fact that the CPU has free access to the FDCAN Message RAM, special care
has to be taken when reading FIFO elements in an arbitrary order (Get Index not
considered). This might be useful when reading a High Priority Message from one of the two
Rx FIFOs. In this case the FIFO Acknowledge Index should not be written because this
would set the Get Index to a wrong position and also alters the FIFO Fill Level. In this case
some of the older FIFO elements would be lost.
Note: The application has to ensure that a valid value is written to the FIFO Acknowledge Index.
The FDCAN does not check for erroneous values.
43.3.5 FDCAN Rx FIFO element
Two Rx FIFOs are configured in the Message RAM. Each Rx FIFO section can be
configured to store up to three received messages. The structure of an Rx FIFO element is
described in
Bit 31
R0 ESI
R1 ANMF
R2
R3
Rn
The element size configured for storage of CAN FD messages is set to 64 bytes data field.
Field
R0 Bit 31
ESI
R0 Bit 30
XTD
R0 Bit 29
RTR
R0 Bits 28:0
ID[28:0]
1924/2083
Table 390, the description is provided in

Table 390. Rx FIFO element

24 23
XTD RTR
FIDX[6:0]
DB3[7:0]
DB7[7:0]
DBm[7:0]

Table 391. Rx FIFO element description

Error state indicator
– 0: Transmitting node is error active
– 1: Transmitting node is error passive
Extended identifier
Signals to the Host whether the received frame has a standard or extended identifier.
– 0: 11-bit standard identifier
– 1: 29-bit extended identifier
Remote transmission request
Signals to the Host whether the received frame is a data frame or a remote frame.
– 0: Received frame is a data frame
– 1: Received frame is a remote frame
Identifier
Standard or extended identifier depending on bit XTD. A standard identifier is stored
into ID[28:18].
RM0440 Rev 1
Table
ID[28:0]
Res. FDF BRS DLC[3:0]
DB2[7:0]
DB6[7:0]
DBm-1[7:0]
Description
391.
16 15 8 7
RXTS[15:0]
DB1[7:0]
DB5[7:0] DB4[7:0]
DBm-2[7:0] DBm-3[7:0]
RM0440
0
D[7:0]