NXP Semiconductors LPC24XX UM10237 - Manual (Page 511)

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User manual Rev. 04 — 26 August 2009 511 of 792
NXP Semiconductors
UM10237
Chapter 18: LPC24XX CAN controllers CAN1/2
17.2 FullCAN interrupts
The CAN Gateway Block contains a 2 kB ID Look-up Table RAM. With this size a
maximum number of 146 FullCAN objects can be defined if the whole Look-up Table RAM
is used for FullCAN objects only. Only the first 64 FullCAN objects can be configured to
participate in the interrupt scheme. It is still possible to define more than 64 FullCAN
objects. The only difference is, that the remaining FullCAN objects will not provide a
FullCAN interrupt.
The FullCAN Interrupt Register-set contains interrupt flags (IntPndx) for (pending)
FullCAN receive interrupts. As soon as a FullCAN message is received, the according
interrupt bit (IntPndx) in the FCAN Interrupt Register gets asserted. In case that the Global
FullCAN Interrupt Enable bit is set, the FullCAN Receive Interrupt is passed to the
Vectored Interrupt Controller.
Application Software has to solve the following:
1. Index/Object number calculation based on the bit position in the FCANIC Interrupt
Register for more than one pending interrupt.
2. Interrupt priority handling if more than one FullCAN receive interrupt is pending.
The software that covers the interrupt priority handling has to assign a receive interrupt
priority to every FullCAN object. If more than one interrupt is pending, then the software
has to decide, which received FullCAN object has to be served next.
To each FullCAN object a new FullCAN Interrupt Enable bit (FCANIntxEn) is added, so
that it is possible to enable or disable FullCAN interrupts for each object individually. The
new Message Lost flag (MsgLstx) is introduced to indicate whether more than one
FullCAN message has been received since last time this message object was read by the
CPU. The Interrupt Enable and the Message Lost bits reside in the existing Look-up Table
RAM.
17.2.1 FullCAN message interrupt enable bit
In Figure 18–83 8 FullCAN Identifiers with their Source CAN Channel are defined in the
FullCAN, Section. The new introduced FullCAN Message Interrupt enable bit can be used
to enable for each FullCAN message an Interrupt.