Hi All,
I have a card with a Bosch CC770 CAN Controller but I have some
problems:
1. I Applied the patch suggested by BOSCH, Ref. CC770 (Stand Alone CAN
Controller) Data Sheet Revision 1.6 30.03.2009
9.1 Description
In chapter chapter 4.2 the description of the EIE bit suggests, that
a change in the error status
will cause an interrupt to be generated. That means, if bits BOff or
Warn in Status register
(01H) are changing from 0 to 1 or vice versa from 1 to 0 an interrupt
will be generated. In
such a case, usually an interrupt routine reads the Interrupt
register (5FH) to determine the
interrupt source and then reads the Status register (01H) to
acknowledge the interrupt and
this deactivates the interrupt line.
The behaviour of the error status Warn is as described, but the
behaviour of the error status
BOff is not as described. The error status BOff does not trigger the
Interrupt register by a
change (edge triggered), but by level. Thus, in Bus Off state, the
Interrupt register is forced
to 01H and hence the interrupt line remains active. The only way to
deactivate the interrupt
line is to reset the IE bit in the Control register, a read to the
Status register has no effect.
9.2 Work-around
On occurrence of a Bus Off interrupt, the CPU shall reset the IE bit
in the Control register to
deactivate the interrupt line. To re-synchronize the CC770 to the CAN
bus, the Bus Off
Recovery Sequence shall be started by resetting the Init bit in the
Control register. After
successful resynchronisation, the BOff flag in the Control register
will be reset by CC770.
The software shall poll for this state and, if reached, it may
re-enable the CC770 interrupt by
setting IE bit in the Control register.
Please note that leaving BusOff state (resetting BOff and Warn bits)
will also cause an Error
interrupt. In this case, reading the Status register clears the
Interrupt register.
And it works properly. Unfortunately now I have some "Stuff Error"
and "Form Error".
The causes of these errors, AFAIK, are:
Stuff Error
1. a disturbance generates more consecutive bits of equal level than
allowed by the rule of
bit stuffing and therefore the error is detected by all nodes.
2. a disturbance falsifies one or more of the five bits preceeding
the stuff bit. This error
is not recognized by a receiver; however, if the error also
appears at the transmitter,
it will be detected as a bit error (transmitter monitors bus as it
transmits).
In any case, the error is detected by a receiver either by the bit
stuffing mechanism (the
stuff bit of the transmitter is not dropped but taken as an
information bit) or by the CRC check.
Form Error
Form Errors result from the violation of the fixed form of the
following bit fields:
- end of frame
- interframe space
- ACK delimiter
- CRC delimiter
During the transmission of these bit fields, an error condition is
recognized if a "dominant" bit
level is detected.
My question is: are these errors detected on the TX side or on the RX
side? It seems to be in TX, as far
as I can understand but I would like to have a confirmation.
2. Where can I find the Linux drivers for the Bosch CC770?
3. I would like to know how the Bus_off problem in the interrupt handler
is managed in the kernel tree.
Thanks in advance for the support
Best Regards
Agostino Sette
TechnoLabs Spa
L'Aquila
Italy
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