[Bug 1001456] HAL misses Interrupt Clear-Pending Registers handling: wasted processing power

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--- Comment #14 from Bernard Fouché <bernard.fouche@kuantic.com> 2012-02-15 11:28:54 GMT ---
(In reply to comment #13)
> Changes to the Kernel should be done with caution. I think that this addition
> is not necessary. The desired functionality, for a given platform, can be
> introduced by #defining HAL_VAR_INTERRUPT_ACKNOWLEDGE (and/or its cousins).

There are two problems:

- clearing the pending interrupt bit is completely different from acknowledging
an interrupt. Acknowledgment is usually done at the end of DSR/ISR while
clearing the pending interrupt bit must be done *before* reading the peripheral
registers describing interrupt source(s): HAL_VAR_INTERRUPT_ACKNOWLEDGE is not
a solution.

- if HAL_VAR_INTERRUPT_CLEAR_PENDING is added only to Cortex-M targets, then
how can one share a driver between an arch not requiring clearing pending
interrupt and Cortex-M cores? For instance the generic serial 16x5x driver?
Today cyg_drv_interrupt_acknowledge() resolves to CYG_EMPTY_STATEMENT for
Cortex-M, IMHO we need cyg_drv_interrupt_clear_pending() to resolve to
CYG_EMPTY_STATEMENT for non-Cortex-M, hence one can write a driver using both
cyg_drv_interrupt_acknowledge() and cyg_drv_interrupt_clear_pending() at the
correct place so the driver can work in different arch.

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Subject: [Bug 1001456] HAL misses Interrupt Clear-Pending Registers handling:
 wasted processing power
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--- Comment #14 from Bernard Fouché <bernard.fouche@kuantic.com> 2012-02-15 11:28:54 GMT ---
(In reply to comment #13)
> Changes to the Kernel should be done with caution. I think that this addition
> is not necessary. The desired functionality, for a given platform, can be
> introduced by #defining HAL_VAR_INTERRUPT_ACKNOWLEDGE (and/or its cousins).

There are two problems:

- clearing the pending interrupt bit is completely different from acknowledging
an interrupt. Acknowledgment is usually done at the end of DSR/ISR while
clearing the pending interrupt bit must be done *before* reading the peripheral
registers describing interrupt source(s): HAL_VAR_INTERRUPT_ACKNOWLEDGE is not
a solution.

- if HAL_VAR_INTERRUPT_CLEAR_PENDING is added only to Cortex-M targets, then
how can one share a driver between an arch not requiring clearing pending
interrupt and Cortex-M cores? For instance the generic serial 16x5x driver?
Today cyg_drv_interrupt_acknowledge() resolves to CYG_EMPTY_STATEMENT for
Cortex-M, IMHO we need cyg_drv_interrupt_clear_pending() to resolve to
CYG_EMPTY_STATEMENT for non-Cortex-M, hence one can write a driver using both
cyg_drv_interrupt_acknowledge() and cyg_drv_interrupt_clear_pending() at the
correct place so the driver can work in different arch.

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Bernard Fouché <bernard.fouche@kuantic.com> changed:

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--- Comment #1 from Bernard Fouché <bernard.fouche@kuantic.com> 2012-02-15 13:46:05 GMT ---
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--- Comment #2 from Bernard Fouché <bernard.fouche@kuantic.com> 2012-02-15 13:46:54 GMT ---
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Bernard Fouché <bernard.fouche@kuantic.com> changed:

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--- Comment #3 from Sergei Gavrikov <sergei.gavrikov@gmail.com> 2012-02-15 20:45:18 GMT ---
On Comment #0
> Try to mimick /dev/null. (inspired by loop serial driver.) Comments
> welcome, maybe the semantics aren't close enough to Un*x but it should
> do the job for most cases. The doc may need to be rewritten?

It seemed to me your interpretation of /dev/null will arise some
confusions for some users. Below are mine.

Mess #1

  I would avoid the same mimic (and naming). In UNIX-like operating
  systems, /dev/null is a special *file* and not a serial device.

  % stty -aF /dev/null
  stty: /dev/null: Inappropriate ioctl for device

As you can see /dev/null is not some terminal line (serial device).
Well, eCos != *nix, but, I would avoid the ability to configure the
/dev/null as a serial device under eCos.

Mess #2

  A read on /dev/null would not block process (thread), it does return
  EOF, and you offer in your documentation to enter an ability of the
  blocking read on /dev/null as an option.

Mess #3

  IMO, if anyone will see those words together in CDL (I mean 'serial'
  and 'null'), under eCos dev/serial/null, then he would think, Great!
  There is 'nullmodem' device in eCos! Come check my guess

    http://www.google.com/search?q=%2Bserial+%2Bnull

  And after reading your documentation, they will think, Nope! They
  provide something very special (special null device :-)

BUT

I do not want to break your idea. IMHO, the main mess here is naming and
your free interpretation of /dev/null. You try to implement some serial
device like a "tear off" nullmodem, but what is bad with a "nullmodem"
abstraction for your purposes? And eCos serial loop driver (as you could
see) is a half of nullmodem itself.

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