I can transmit, but rx buffers never get message...help!

Greetings all.  My first step into the CAN world occurred a few months
ago.

Please, if you have any ideas regarding the following, don't hesitate
to offer them up!

We are in the throes of designing a CAN based control system for
automobile simulators.  We are using MC9S12DP256 microcontroller from
Motorola/Freescale - we have some development boards right now.

I am using a high speed TI transceiver (SN65HVD251) and set baud rate
to 1Mb/s.

After much pain (especially in bit timing!), I am successfully
transmitting messages between development boards and back to the PC
(through IXXAT USBtoCAN device).  The data I send does get transmitted
and shows no errors.  I can see the data displayed on the PC, and I can
see the data on the bus with an oscilloscope.

The development boards don't receive the message properly, however.
Each board sends the ACK signal, and no errors are generated.  But the
RXF flag never goes high - indicating the message is not passing the
filtering (acceptance code/mask) setup.

Because the receive buffers never get populated with a message, no
interrupt ever fires and all nodes happily ignore any and all messages
I've tried.

I have tried the filters in many different configurations, including
actually following the datasheet directions, and I am still not
successful.

If you have any pointers, ideas, or condolences I'd love to hear them.

Also, I suppose it could be another issue, but I'm not convinced yet.

Thank you,

David Havell
Sr Electrical Engineer
L3 Communications
SLC UT 84104

david.havell@l-3com.com wrote:

> Greetings all.  My first step into the CAN world occurred a few months
> ago.
> 
> Please, if you have any ideas regarding the following, don't hesitate
> to offer them up!
> 
> We are in the throes of designing a CAN based control system for
> automobile simulators.  We are using MC9S12DP256 microcontroller from
> Motorola/Freescale - we have some development boards right now.
> 
> I am using a high speed TI transceiver (SN65HVD251) and set baud rate
> to 1Mb/s.
> 
> After much pain (especially in bit timing!), I am successfully
> transmitting messages between development boards and back to the PC
> (through IXXAT USBtoCAN device).  The data I send does get transmitted
> and shows no errors.  I can see the data displayed on the PC, and I can
> see the data on the bus with an oscilloscope.
> 
> The development boards don't receive the message properly, however.
> Each board sends the ACK signal, and no errors are generated.  But the
> RXF flag never goes high - indicating the message is not passing the
> filtering (acceptance code/mask) setup.
> 
> Because the receive buffers never get populated with a message, no
> interrupt ever fires and all nodes happily ignore any and all messages
> I've tried.
> 
> I have tried the filters in many different configurations, including
> actually following the datasheet directions, and I am still not
> successful.
> 
> If you have any pointers, ideas, or condolences I'd love to hear them.
> 
> Also, I suppose it could be another issue, but I'm not convinced yet.
> 

The ACK is a hardware function -- a node sends it when it detects a 
valid packet, whether it does anything with it or not.

Try setting the acceptance masks to all ones, then all zeros.  One of 
these should be "I'll take anything".  If that doesn't work then there's 
probably some other obscure bit -- perhaps not one that's described in 
the CAN section of the manual -- that you need to set up.

Does Freescale have any example code you could try?

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Tim Wescott wrote:
> david.havell@l-3com.com wrote:
>
> > Greetings all.  My first step into the CAN world occurred a few
months
> > ago.
> >
> > Please, if you have any ideas regarding the following, don't
hesitate
> > to offer them up!
> >
> > We are in the throes of designing a CAN based control system for
> > automobile simulators.  We are using MC9S12DP256 microcontroller
from
> > Motorola/Freescale - we have some development boards right now.
> >
> > I am using a high speed TI transceiver (SN65HVD251) and set baud
rate
> > to 1Mb/s.
> >
> > After much pain (especially in bit timing!), I am successfully
> > transmitting messages between development boards and back to the PC
> > (through IXXAT USBtoCAN device).  The data I send does get
transmitted
> > and shows no errors.  I can see the data displayed on the PC, and I
can
> > see the data on the bus with an oscilloscope.
> >
> > The development boards don't receive the message properly, however.
> > Each board sends the ACK signal, and no errors are generated.  But
the
> > RXF flag never goes high - indicating the message is not passing
the
> > filtering (acceptance code/mask) setup.
> >
> > Because the receive buffers never get populated with a message, no
> > interrupt ever fires and all nodes happily ignore any and all
messages
> > I've tried.
> >
> > I have tried the filters in many different configurations,
including
> > actually following the datasheet directions, and I am still not
> > successful.
> >
> > If you have any pointers, ideas, or condolences I'd love to hear
them.
> >
> > Also, I suppose it could be another issue, but I'm not convinced
yet.
> >
>
> The ACK is a hardware function -- a node sends it when it detects a
> valid packet, whether it does anything with it or not.
>
> Try setting the acceptance masks to all ones, then all zeros.  One of

> these should be "I'll take anything".  If that doesn't work then
there's
> probably some other obscure bit -- perhaps not one that's described
in
> the CAN section of the manual -- that you need to set up.
>
> Does Freescale have any example code you could try?
>
> --
>
> Tim Wescott
> Wescott Design Services
> http://www.wescottdesign.com


Yes, the ACK is generated on a valid message.  Which is why I suspect
my problem is in the Rx filtering setup.

I have tried all sorts of combinations, but not all 1's.  That's a good
idea.  I will try that this morning.

Someone else mentioned setting both registers to 1's also, strangely
not mentioned in the documentation I have.

I have asked Freescale directly on exactly how to set up the filters.
Thanks for your recommendations, I really appreciate it.

David Havell
L3 Communications