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

C Smith csmithquestions at gmail.com
Thu May 24 09:24:26 CEST 2018

Jan Kiska wrote:
>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 trust the EOI is taken care of automatically, as you say.

However I am on a special industrial motherboard whose BIOS allows the use
of IRQ 5 for certain serial ports. There is no mistake, I chose IRQ 5 in
the BIOS (only choices are 5 and 10, but 10 conflicts with a PCI card).
Here is the kernel's dmesg at boot:
[    0.536089] 00:05: ttyS1 at I/O 0x2f8 (irq = 5, base_baud = 115200) is a
Here is setserial /dev/ttyS1 after boot:
/dev/ttyS1, UART: 16550A, Port: 0x02f8, IRQ: 5

When xeno_16550A module is invoked with one of the ports on IRQ 5 like this:
xeno_16550A io=0x02e0,0x02f8,0x3f8 irq=10,5,4 baud_base=115200,115200,115200
The port at 0x02f8 IRQ 5 behaves fine and transmits and receives OK.

But when the xeno_16550A module is invoked with more than one of the ports
set to IRQ 5 in the BIOS like this:
xeno_16550A io=0x02e0,0x02f8,0x03e8,0x02e8 irq=5,5,5,5
All those ports fail to work, only one byte can be transmitted or received.

On this same motherboard, a Moxa PCI card can share IRQ17 between 4 ports
OK using xeno_16550A, demonstrating that the kernel/modules are compiled
But there seems to be a problem with sharing IRQ 5.

-C Smith

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