NEC MuPD70F3187, User Manual

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Chapter 18 AFCAN Controller
User’s Manual U16580EE3V1UD00
If the LIPT pointer is incremented and matches the value of the RGPT pointer minus 1, the ROVF bit
(receive history list overflow) of the CnRGPT register is set to 1. This indicates that the RHL is full of
numbers of message buffers that have not been read. When further message reception and storing
occur, the last recorded message buffer number is overwritten by the number of the message buffer that
received and stored the newly received message. In this case, after the ROVF bit has been set (1), the
recorded message buffer numbers in the RHL do not completely reflect the chronological order. How-
ever messages itself are not lost and can be located by CPU search in message buffer memory with the
help of the DN-bit.
Caution: If the history list is in the overflow condition (ROVF is set), reading the history list
contents is still possible, until the history list is empty (indicated by RHPM flag set).
Nevertheless, the history list remains in the overflow condition, until ROVF is cleared
by software. If ROVF is not cleared, the RHPM flag will also not be updated (cleared)
upon a message storage of newly received frame. This may lead to the situation, that
RHPM indicates an empty history list, although a reception has taken place, while the
history list is in the overflow state (ROVF and RHPM are set).
As long as the RHL contains 23 or less entries the sequence of occurrence is maintained. If more
receptions occur without reading the RHL by the host processor, complete sequence of receptions can
not be recovered.
Figure 18-29: Receive history list
2 3
1
2
3
4
5
6
7
Receive hi s tory li s t (RHL)
2 3
1
2
3
4
5
6
7
Receive hi s tory li s t(RHL)
L as t in-me ssa ge
pointer(LIPT)
2 3
0
1
2
3
4
5
6
7
2 3
1
2
3
4
5
6
7
0
:
:
:
:
:
:
:
:
:
22
0
0
22
22
22
Me ssa ge bu ffer 7
Me ssa ge bu ffer 2
Me ssa ge bu ffer 9
Me ssa ge bu ffer 6
Me ssa ge bu ffer 8
Me ssa ge bu ffer 4
Me ssa ge bu ffer 3
Receive hi s tory
li s t get pointer
(RGPT)
Receive hi s tory li s t(RHL)
Me ssa ge bu ffer 1
Me ssa ge bu ffer 5
Me ssa ge bu ffer 8
Me ssa ge bu ffer 4
Me ssa ge bu ffer 3
Me ssa ge bu ffer 10
Me ssa ge bu ffer 6
Me ssa ge bu ffer 11
Me ssa ge bu ffer 9
Receive hi s tory
li s t get pointer
(RGPT)
L as t in-me ssa ge
pointer(LIPT)
ROVF = 1
LIPT i
s b locked.
Receive hi s tory
li s t get pointer
(RGPT)
Receive hi s tory
li s t get pointer
(RGPT)
L as t in-me ssa ge
pointer(LIPT)
Me ssa ge bu ffer 1
Me ssa ge bu ffer 9
Me ssa ge bu ffer 10
Me ssa ge bu ffer 5
Me ssa ge bu ffer 3
Me ssa ge bu ffer 4
Me ssa ge bu ffer 8
Me ssa ge bu ffer 11
Receive hi s tory li s t (RHL)
L as t in-me ssa ge
pointer(LIPT)
ROVF = 1
LIPT i
s b locked.
Me ssa ge bu ffer 15
Event:
- me
ssa ge bu ffer 6, 9, 2 a nd 7
a re re a d b y ho s t proce ss or.
- Newly received me ssa ge s
a re s tored in me ssa ge bu ffer
3 , 4 a nd 8 .
Event:
- reception in me
ssa ge bu ffer 1 3 , 14
a nd 15 occ u r s .
- Overflow s it ua tion occ u r s .
Event:
- 20 other me
ssa ge s a re received.
Me ssa ge bu ffer 6 c a rrie s l as t received me ssa ge.
- Upon reception in me ssa ge bu ffer 6, RHL i s f u ll.
- ROVF i s s et.
ROVF = 1 define s th a t LIPT e qua l s RGPT - 1 while me ssa ge bu ffer n u m b er s tored to element indic a ted b y LIPT - 1.