Re: Coldfire V2 devices and serial debuggers

Chris Johns wrote:

[...]

>The BDM protocol will support access to certain CPU resources while the 
>program is running. The Sourceforge tools provide an open source library of 
>code with calls that allow access to the BDM protocol. If BDM allows it the 
>BDM drivers and support libraries will also allow it. There are how-ever some 
>constraints that make what you want difficult with BDM. The main one is CPU 
>registers are not accessible when the processor is running. This means 
>variables held in registers will not be seen and the same goes for the PC so 
>now does the external host program know where the PC is and where to step next.

As long as we talk about watching a running program, this will apply
to a serial debugger as well - a serial debugger won't show local
variables on stack or in registers of a running application.

Just peeking global or static variables via Coldfire V2 BDM has
minimal impact (a small number of CPU cycles for each access). With a
serial debugger, you could control _when_ the CPU is interrupted, but
in total the handling would take longer => more load.

And you have better control over the CPU, BDM doesn't need a
bootloader etc. If your application disables interrupts, you might be
out of luck with a serial debugger.

As I wrote, if someone needs single step debugging of one task while
an interrupt service routine is still running, a good serial debugger
might be better. A bad debugger might crash also if interrupts remain
enabled during single step etc.

If you are willing to spend some money, you get very nice BDM
debuggers saving a lot of time.

Be aware that there might be BDM debuggers _not_ allowing realtime
variable watch but indeed halting the CPU for hundreds of
microseconds. I heared about Codeworrier doing so, but I didn't test
it myself.

Oliver

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