[ECOS] nested interrupts

[Xavier Wang]

> 
> As I was explained here, a main purpose of a DSR is to avoid 
> scheduler's ready list manipulation from an interrupt. DSR mechanism 
> serializes access to the scheduler (to suspend or resume a thread, or 
> to send a message), thus completely avoiding disabling interrupts when 
> posting. Quite neat. There is a price to pay, however, since DSR 
> mechanism nearly doubles the time between posting interrupt and thread 
> resumption. Bearing this in mind, the only thing DSR absolutely has to 
> do is to notify the scheduler. All the rest ought to be done either in 
> an ISR or in a thread.
> 
> Regards,
> Sergei Slobodov

Thanks for your explanation. But as I knew, ISRs should be as short as
possible to reduce the time of masking interrupts and other non-critical
stuff can be processed in DSRs. So I don't understand what the following
means:

    "Bearing this in mind, the only thing DSR absolutely has to do is to
    notify the scheduler. All the rest ought to be done either in an ISR or
    in a thread."