Date: Sat, 29 Nov 1997 23:25:37 GMT From: jak@cetlink.net (John Kelly) To: Bruce Evans <bde@zeta.org.au> Cc: hackers@freebsd.org Subject: Re: 650 UART, SIO driver, 8259 PIC Message-ID: <3481a093.3224591@mail.cetlink.net> In-Reply-To: <199711292017.HAA16179@godzilla.zeta.org.au> References: <199711292017.HAA16179@godzilla.zeta.org.au>
next in thread | previous in thread | raw e-mail | index | archive | help
On Sun, 30 Nov 1997 07:17:23 +1100, Bruce Evans <bde@zeta.org.au> wrote: >BTW, I remember why an EOI is sent on return and not at the start >for the non-auto-EOI case. That was my next question. :-) >It is to reduce interrupt latency. I guess that depends on how you measure latency. But it seems that the requesting device must wait the same length of time to get service either way, at least in the case where the ISR leaves CPU interrupts disabled until exiting with IRET automatically reenables them. Perhaps EOI at the start (like auto-EOI) would be useful if the ISR reenabled CPU interrupts to allow other devices to pre-empt the current ISR. John
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?3481a093.3224591>