Disabling system clock to use external clock driver card

[Gedare Bloom]

On Fri, Mar 4, 2016 at 9:46 AM, Michael Westfall <mwestfal at gemini.edu> wrote:
> Hello,
>
> We have a vxWorks driver for a VME IRIG-B time provider card (Bancomm
> bc635/bc637) which we want to port to  RTEMS.
>
> The ISR of the current vxWorks driver disables the system clock via
> sysClkDisable() in order to take over providing ticks to the kernel via
> tickAnnounce().
>
> rtems_clock_tick() seems to be a direct replacement for the tickAnnounce()
> function, but what is the strategy for disabling/reenabling the system
> clock?
>
> Surely someone else has implemented something similar.
>
You should be able to provide a custom clock source for the clock
driver at the BSP level. Most (all?) BSPs use the framework in
c/src/lib/libbsp/shared/clockdrv_shell.h to drive the system clock
ticks by implementing the necessary "hook" functions. You can
replace/modify the BSP's ckinit.c to use the bc635 card instead. See
for example c/src/lib/libbsp/i386/pc386/clock/ckinit.c for how the x86
currently has two options for the clock timer.

This would relieve you from having to track quite so much "state".
However, I suppose if you wanted to just port your code below, you
would replace the Clock_isr with this code, and undo the
Clock_driver_support_initialize_hardware() that your BSP has done.

>
> Here is our vxWorks ISR:
>
> void isr_bc635
> (
>  void *parg
>  )
> {
>    register short intnum;
>    register unsigned short tmask, bcistatus, bcimask;
>
>    bcistatus = pbc635->intstat; /* Save copy of status register */
>    bcimask   = pbc635->mask; /* Save copy of interrupt mask */
>    /* First check for periodic interrupt */
>    if ( ((bcistatus & 0x02) & bcimask) != 0)
>    {
>       if (bcUseper) /* Using BC periodics for system clock? */
>       {
>          if (!HadPerint) /* First Periodic Interrupt? */
>          {
>             HadPerint = TRUE;
>             sysClkDisable(); /* Turn off system clock interrupts */
>             sysClkRateSet(tickFrequency); /* set clock rate */
>          }
>          bcIntCounter++; /* Increment interrupt count */
>          if (bcUsrClock != NULL) (*bcUsrClock)(bcIntCounter); /* Call user
> routine */
>          if (bcIntCounter%bcIntPerTick == 0) /* If right number of ticks */
>             tickAnnounce(); /* Announce system clock tick */
>       }
>       pbc635->intstat = pbc635->intstat | 0x02; /* Clear interrupt status
> bit */
>    }
>    /* Other interrupts - not periodic pulse */
>    for (intnum = 1; intnum < 5; intnum++)
>    {
>       if (intnum != 2)
>       {
>          tmask = 0x01 << (intnum - 1); /* Test value for interrupt */
>          /* Check for interrupt bit set - request I/O scan, but only if
> ioscanpvt is valid */
>          if ( ((bcistatus & tmask) & bcimask) != 0)
>          {
>             if (ioscanpvt[intnum-1] != NULL)
>                scanIoRequest(ioscanpvt[intnum-1]);
>             pbc635->intstat = pbc635->intstat | tmask;   /* Clear interrupt
> status bit */
>          }
>       }
>    }
> }
>
>
> --
> Mike Westfall
> Gemini Observatory
>
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