Re: MCF547X bus error

How about enableing a spare chip select to cover all the space not 
covered by your responding memories. Then tie the spare chip select back 
to an interrupt.

Dave


nop head wrote:
> Is it me or are Freescale making it harder and harder to make a robust 
> system?
>
> I need to stop illegal accesses hanging the system. 15 years ago we 
> had a 68340 with a bus error timer that terminated any bad cycles and 
> caused an exception. Before that a simple counter on the BERR pin did 
> the same thing.
>
> A couple of years ago we moved to MCF537X. To get the same 
> functionality we had to add an external bus timer which generated a TA 
> and a level 7 interrupt if it saw a TS with no following FBCSn.
>
> With the MC547X I find that it does not generate ALE for cycles that 
> miss the Flex Bus chip select range, so my only option seems to be an 
> external watchdog timer which, when it times out generates a TA pulse 
> and an interrupt. A not insignificant amount of logic and design time 
> that could be done much better inside the core with a trivial amount 
> of silicon.
>
> It does have three watchdog timers on the XL Bus, but they don't seem 
> to be of any use for this situation. What would cause an XL bus timeout?
>
> There is also a watchdog timer in the SIU, which misleadingly is shown 
> as a separate timer, but is actually GPT0. But that only seems to 
> generate a reset, making debugging the problem impossible.
>
> Even with an interrupt it will be very difficult to pinpoint the 
> errant instruction. I thought I could use the MMU to help me, but I 
> find that when the MMU is enabled I lose the default cache settings. 
> My default is no caching for I/O and I have two data ACR settings, one 
> for write through non-volatile memory sections and another for 
> buffered copy back for DRAM. So am I right in thinking that with the 
> MMU enabled I have to have one of the data ACRs set to no caching for  
> the I/O addresses leaving me with only one other type of data cache mode?
>
> Is it really this hard or have I missed something in the manual?
>
>
>
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