[Xenomai] Only 2 serial ports at a time with xeno_16550A driver

Jan Kiszka jan.kiszka at siemens.com
Wed May 23 11:18:04 CEST 2018


On 2018-05-23 07:25, C Smith wrote:
> I'm not familiar with the chaining of shared interrupts in the RTDM
> architecture. I think the EOI should somehow be done in the very last
> invocation of rt_16550_interrupt() by the last peripheral needing service.
> 

Just like under Linux, the driver does not have to worry about that
details. Xenomai will EOI the IRQ when needed. The driver handler just
need to tell if a particular invocation was (also) triggered by the
device it drives.

> 
> I read this from an old interrupt handler:
> (assuming IBM PC (Intel) architecture)
> An interrupt handler issues an EOI by writing the value 0x20 to the PIC at
> address 0x20. If the interrupt was number 8-15, do the same thing again,
> write 0x20 to address 0x20.
> 
> So perhaps something like this at the end of rt_16550_interrupt() ?
> 
> if (ctx->irq_handle.irq <= 7)        /* non-specific EOI to 8259 */
>   rt_16550_reg_out(mode, 0, 0x20, 0x20);
> if (ctx->irq_handle.irq <= 15)          /* extra EOI for upper ISA IRQs */
>   rt_16550_reg_out(mode, 0, 0x20, 0x20);
> 
> But again I don't know if that will work with shared interrupts. Surely
> RTDM implements some "master" handler which is already doing an EOI?
> Remember lower interrupts like IRQ 5 work fine with the xeno_16550A driver

As noted in the other thread, IRQ 5 is most probably wrong. Check what
Linux uses when you attach the device to a normal Linux driver.

Jan

> unless another port is sharing the same IRQ.
> 
> -C Smith
> 

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Corporate Competence Center Embedded Linux



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