Re: [ECOS] problems with small CYGNUM_HAL_RTC_PERIOD

[Jonathan Larmour <jifl at eCosCentric dot com>]

David N. Welton wrote:
> I have an experimental app that drives the PC speaker.
>
> CYGNUM_HAL_RTC_PERIOD is, on the i386 platform, normally defined as
> 11932, making for 100 ticks per second.  That's not very fine grained
> for what I want to do.
>
> 1) Is there any way to do some sort of sleep/alarm/whatever in less
>    than a tick? I don't think so, but just checking...
You can probably use a hal_delay_us which does a busy wait reading the 
hardware timer. A busy wait isn't necessarily what you want though.

> 2) I drop that number down to 1193, and things work ok, but I try and
>    drop it further to 119, and the system no longer seems to respond
>    to events (keyboard interrupts, to be specific).  Same problem with
>    alarms.  Any idea what could be going on?
If you change the period, you also have to change the clock resolution 
numerator/denominator too. That way the kernel knows how to map the clock 
interrupt frequency to real elapsed time.

You can find the CYGNUM_HAL_RTC_NUMERATOR aloingside the period option in 
the pcmb package. If you reduce the period by a factor of 100, reduce the 
numerator by a factor of 100.

> BTW, on a completely unrelated note,
>
> #ifdef KEYBOARD_EN_US
> #include <cyg/hal/pcmb_keyboard_en_us.h>
> #else if ....
> #include <cyg/hal/pcmb_keyboard_en_gb.h>
> ...
>
> with an accompanying bit of CDL would be convenient in pcmb_screen.c
> in order to pick whichever keyboard is the most convenient.
> Unfortunately, I couldn't quite get the CDL right to make this work
> well enough to submit a patch.
Something like the following at the bottom of hal_i386_pcmb.cdl:

cdl_option CYGSEM_HAL_I386_PCMB_KEYBOARD_LAYOUT {
  display "Keyboard layout for diagnostic console"
  legal_values { "US" "GB" }
  default_value { "US" }
  active_if CYGINT_HAL_I386_PCMB_SCREEN_SUPPORT
  description "
     This option allows the changing of keyboard layout when used with
     the PC screen and keyboard diagnostic console."
}

Then in the code use a test like:

#if defined( CYGSEM_HAL_I386_PCMB_KEYBOARD_LAYOUT_US )
...
#elif defined( CYGSEM_HAL_I386_PCMB_KEYBOARD_LAYOUT_GB )
...
#else
# error Unsupported keyboard layout
#endif

Jifl
--
eCosCentric       http://www.eCosCentric.com/       <info@eCosCentric.com>
--[ "You can complain because roses have thorns, or you ]--
--[  can rejoice because thorns have roses." -Lincoln   ]-- Opinions==mine


--
Before posting, please read the FAQ: http://sources.redhat.com/fom/ecos
and search the list archive: http://sources.redhat.com/ml/ecos-discuss