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Re: nested interrupts
- To: "Xavier Wang" <xavierwang at ms19 dot url dot com dot tw>
- Subject: Re: [ECOS] nested interrupts
- From: Jesper Skov <jskov at redhat dot com>
- Date: 18 Jan 2001 10:03:15 +0100
- Cc: <ecos-discuss at sources dot redhat dot com>
- References: <003b01c0811f$196395e0$6f2314ac@realtek.com.tw>
>>>>> "Xavier" == Xavier Wang <xavierwang@ms19.url.com.tw> writes:
Xavier> I got confused about nested interrupts. In
Xavier> http://sources.redhat.com/ecos/docs-latest/porting/hal-interrupts.html
Xavier> it seems that interrupts are disabled in ISRs, but enabled in
Xavier> DSRs.
Xavier> But Hugo's description in the same page said that
Xavier> higher priority interrupts are enabled before calling
Xavier> ISR. Which is true for nested interrupts?
Both are true, but depending on configuration. There is an option that
allows nested interrupts - when disabled, the former is valid, when
enabled, the latter is valid.
Xavier> If it's the former, should I rewrite the 'hal_cpu_int_enable'
Xavier> macro used in hal_interrupt_stack_call_pending_DSRs (in
Xavier> vector.S) to enable only higher priority interrupts? If it's
No. All interrupts are allowed when executing DSRs. DSRs are only
executin when no interrupts are pending.
Xavier> the latter, what should I do to support nested interrupts?
Xavier> (I'm using TX39/JMR3904 platform, eCos version 1.3.1)
You need code that enabled higher level interrupts depending on the
state of CYGSEM_HAL_COMMON_INTERRUPTS_ALLOW_NESTING.
The code needs to go either somewhere in vectors.S around the place
where the hal_cpu_except_enable macro is called. I don't know if a
variant/platform specific version of that macro would be a suitable
solution. None of the other MIPS platforms allow nested interrupts.
Xavier> Besides, by looking into the source code, it seems that if
Xavier> there is any pending DSRs, no thread will be run. So can a
Xavier> high priority thread be blocked by a low priority interrupt
Xavier> (DSR)?
Yes.
Xavier> Will it introduce some problems for a real-time application?
I guess that depends on how you program the DSRs/threads. But I don't
have anything intelligent to say to that, so I won't.
Jesper