cvs commit: src/sys/dev/uart uart_dev_ns8250.c

[Roman Kurakin]

Bruce Evans wrote:

>On Wed, 26 May 2004, Thomas Moestl wrote:
>
>  
>
>>tmm         2004/05/26 14:59:01 PDT
>>
>>  FreeBSD src repository
>>
>>  Modified files:
>>    sys/dev/uart         uart_dev_ns8250.c
>>  Log:
>>  It seems that clearing the MCR_IE bit in the modem control register
>>  does not reliably prevent the triggering of interrupts for all supported
>>  configurations. Thus, the FIFO size probe could cause an interrupt,
>>  which could lead to an interrupt storm in the shared interrupt case.
>>    
>>
>
>s/It seems that clearing/Clearing/.  Clearing MCR_IE disables the device's
>line driver for the irq.  At least on old i386 isa systems, the line driver
>is normally connected to a tri-state latch which floats high due to a weak
>pullup when all its inputs are disabled.  So "disabling" interrupts by
>  
>
As far as I know some modern UARTS do not support this feature.
For example, Exar 17C158.

rik