[ECOS] Possible loss of PowerPC mpc8xx Interrupts

[Jonathan Larmour]

[ Excuse my top posting - it's a one-off ]

Looks right to me. I'll check this in tomorrow unless someone (Hi Gary 
:-)) objects.

Jifl

Retallack, Mark (Poole) wrote:
> We have found a problem that could cause the loss of edge triggered
> interrupts.
> 
> The following section of code is from the
> \hal\powerpc\mpc8xx\current\include\var_initr.h file, in function
> cyg_hal_interrupt_acknowledge:
> 
>     case CYGNUM_HAL_INTERRUPT_SIU_IRQ0 ... CYGNUM_HAL_INTERRUPT_SIU_LVL7:
>     {
>         // SIU interrupt vectors
>         cyg_uint32 sipend;
> 
>         // When IRQx is configured as an edge interrupt it needs to be
>         // cleared. Write to INTx and IRQ/level bits are ignore so
>         // it's safe to do always.
>         HAL_READ_UINT32 (CYGARC_REG_IMM_SIPEND, sipend);
>         sipend |= (((cyg_uint32) CYGARC_REG_IMM_SIPEND_IRQ0) 
>                    >> (vector - CYGNUM_HAL_INTERRUPT_SIU_IRQ0));
>         HAL_WRITE_UINT32 (CYGARC_REG_IMM_SIPEND, sipend);
>         break;
>     }
> 
> In the MPC850 user manual, it states that:
> 
> 	"If an IRQ pin is defined as an edge interrupt, the corresponding
> bit being set indicates that a falling edge was detected on the line and are
> reset by writing ones to them."
> 
> This means that if an edge triggered interrupt comes in just after another
> interrupt (while the first interrupt is executing) and the
> cyg_hal_interrupt_acknowledge function is called, the second interrupt will
> be lost and will nether be serviced.
> 
> The HAL_READ_UINT32 will read the SIPEND register which will contain two
> bits that are set (one for each interrupt) this will then be written back to
> the SIPEND register and will clear both interrupts. 
> 
> A better solution could be to use:
> 
>         sipend = (((cyg_uint32) CYGARC_REG_IMM_SIPEND_IRQ0) 
>                    >> (vector - CYGNUM_HAL_INTERRUPT_SIU_IRQ0));
>         HAL_WRITE_UINT32 (CYGARC_REG_IMM_SIPEND, sipend);
> 
> Is this correct are am I just using the cyg_hal_interrupt_acknowledge
> incorrectly? 


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