NXP Semiconductors LPC24XX UM10237 - Manual (Page 515)

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User manual Rev. 04 — 26 August 2009 515 of 792
NXP Semiconductors
UM10237
Chapter 18: LPC24XX CAN controllers CAN1/2
17.3.3 Scenario 3: Message gets overwritten indicated by Semaphore bits
This scenario is a special case in which the lost message is indicated by the existing
semaphore bits. The scenario is entered, if during a Software read of a message object
another new message gets stored by the message handler. In this case, the FullCAN
Interrupt bit gets set for a second time with the 2
nd Object write.
17.3.4 Scenario 3.1: Message gets overwritten indicated by Semaphore bits and
Message Lost
This scenario is a sub-case to Scenario 3 in which the lost message is indicated by the
existing semaphore bits and by Message Lost.
Fig 87. Message gets overwritten
01 11 01 11 00 00
1st Object
write
2nd Object
write
2nd Object
read
1st Object read
Interrupt Service
Routine
IntPndx
semaphore
bits
look-up
table
access
MsgLostx
message
handler
access
ARM
processor
access
read
SEM
read
D2
read
D1
clear
SEM read
SEM
write
SEM write
D2
write
D1
write
ID,
SEM
write
SEM write
D2
write
D1
write
ID,
SEM
read
SEM
read
D2
read
D1
clear
SEM