Chapter 22 FlexCAN
MPC5602P Microcontroller Reference Manual, Rev. 4
Freescale Semiconductor
565
Note that the received ID field is always stored in the matching MB, thus the contents of the ID field in an
MB may change if the match was due to masking. Note also that FlexCAN does receive frames transmitted
by itself if there exists an Rx matching MB, provided the SRX_DIS bit in the MCR is not asserted. If
SRX_DIS is asserted, FlexCAN will not store frames transmitted by itself in any MB, even if it contains
a matching MB, and no interrupt flag or interrupt signal will be generated due to the frame reception.
To be able to receive CAN frames through the FIFO, the CPU must enable and configure the FIFO during
Freeze Mode (see
). Upon receiving the frames available interrupt from FIFO,
the CPU should service the received frame using the following procedure:
1. Read the Control and Status word (optional – needed only if a mask was used for IDE and RTR
bits)
2. Read the ID field (optional – needed only if a mask was used)
3. Read the Data field
4. Clear the frames available interrupt (mandatory – release the buffer and allow the CPU to read the
next FIFO entry)
22.4.5
Matching process
The matching process is an algorithm executed by the MBM that scans the MB memory looking for Rx
MBs programmed with the same ID as the one received from the CAN bus. If the FIFO is enabled, the
8-entry ID table from FIFO is scanned first and then, if a match is not found within the FIFO table, the
other MBs are scanned. In the event that the FIFO is full, the matching algorithm will always look for a
matching MB outside the FIFO region.
When the frame is received, it is temporarily stored in a hidden auxiliary MB called Serial Message Buffer
(SMB). The matching process takes place during the CRC field of the received frame. If a matching ID is
found in the FIFO table or in one of the regular MBs, the contents of the SMB will be transferred to the
FIFO or to the matched MB during the 6th bit of the End-Of-Frame field of the CAN protocol. This
operation is called “move-in”. If any protocol error (CRC, ACK, etc.) is detected, than the move-in
operation does not happen.
For the regular mailbox MBs, an MB is said to be “free to receive” a new frame if the following conditions
are satisfied:
•
The MB is not locked (see
Section 22.4.6.3, “Message Buffer lock mechanism
•
The Code field is either EMPTY or else it is FULL or OVERRUN but the CPU has already serviced
the MB (read the C/S word and then unlocked the MB)
If the first MB with a matching ID is not “free to receive” the new frame, then the matching algorithm
keeps looking for another free MB until it finds one. If it can not find one that is free, then it will overwrite
the last matching MB (unless it is locked) and set the Code field to OVERRUN (refer to
and
). If the last matching MB is locked, then the new message remains in the SMB, waiting for the
Section 22.4.6.3, “Message Buffer lock mechanism
).
Suppose, for example, that the FIFO is disabled and there are two MBs with the same ID, and FlexCAN
starts receiving messages with that ID. Let us say that these MBs are the second and the fifth in the array.
When the first message arrives, the matching algorithm will find the first match in MB number 2. The code
Содержание SAFE ASSURE Qorivva MPC5601P
Страница 2: ...MPC5602P Microcontroller Reference Manual Rev 4 2 Freescale Semiconductor ...
Страница 4: ...MPC5602P Microcontroller Reference Manual Rev 4 4 Freescale Semiconductor ...
Страница 62: ...Chapter 2 MPC5602P Memory Map MPC5602P Microcontroller Reference Manual Rev 4 62 Freescale Semiconductor ...
Страница 104: ...Chapter 4 Clock Description MPC5602P Microcontroller Reference Manual Rev 4 104 Freescale Semiconductor ...
Страница 128: ...Chapter 6 Power Control Unit MC_PCU MPC5602P Microcontroller Reference Manual Rev 4 128 Freescale Semiconductor ...
Страница 272: ...Chapter 12 e200z0 and e200z0h Core MPC5602P Microcontroller Reference Manual Rev 4 272 Freescale Semiconductor ...
Страница 280: ...Chapter 14 Crossbar Switch XBAR MPC5602P Microcontroller Reference Manual Rev 4 280 Freescale Semiconductor ...
Страница 306: ...Chapter 16 Internal Static RAM SRAM MPC5602P Microcontroller Reference Manual Rev 4 306 Freescale Semiconductor ...
Страница 380: ...Chapter 17 Flash Memory MPC5602P Microcontroller Reference Manual Rev 4 380 Freescale Semiconductor ...
Страница 532: ...Chapter 21 LIN Controller LINFlex MPC5602P Microcontroller Reference Manual Rev 4 532 Freescale Semiconductor ...
Страница 578: ...Chapter 22 FlexCAN MPC5602P Microcontroller Reference Manual Rev 4 578 Freescale Semiconductor ...
Страница 708: ...Chapter 25 FlexPWM MPC5602P Microcontroller Reference Manual Rev 4 708 Freescale Semiconductor ...
Страница 742: ...Chapter 26 eTimer MPC5602P Microcontroller Reference Manual Rev 4 742 Freescale Semiconductor ...
Страница 760: ...Chapter 27 Functional Safety MPC5602P Microcontroller Reference Manual Rev 4 760 Freescale Semiconductor ...
Страница 782: ...Chapter 28 Fault Collection Unit FCU MPC5602P Microcontroller Reference Manual Rev 4 782 Freescale Semiconductor ...
Страница 788: ...Chapter 29 Wakeup Unit WKPU MPC5602P Microcontroller Reference Manual Rev 4 788 Freescale Semiconductor ...
Страница 798: ...Chapter 30 Periodic Interrupt Timer PIT MPC5602P Microcontroller Reference Manual Rev 4 798 Freescale Semiconductor ...
Страница 816: ...Chapter 32 Cyclic Redundancy Check CRC MPC5602P Microcontroller Reference Manual Rev 4 816 Freescale Semiconductor ...
Страница 848: ...Chapter 33 Boot Assist Module BAM MPC5602P Microcontroller Reference Manual Rev 4 848 Freescale Semiconductor ...
Страница 930: ...Chapter 36 Nexus Development Interface NDI MPC5602P Microcontroller Reference Manual Rev 4 930 Freescale Semiconductor ...