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jump instruction in delay slot

To: "Linux/MIPS Development" <linux-mips@linux-mips.org>
Subject: jump instruction in delay slot
From: Thomas Koeller <thomas.koeller@baslerweb.com>
Date: Tue, 19 Oct 2004 16:05:47 +0200
Cc: Manish Lachwani <mlachwani@mvista.com>
Organization: Basler AG
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
User-agent: KMail/1.6.2
Hi,

the following code snippet is from
arch/mips/pmc-sierra/yosemite/irq-handler.S:

ll_duart_irq:
                li      a0, 4
                move    a1, sp
                jal     do_IRQ
                j       ret_from_irq

I wonder if this is correct. AFAIK, a jump instruction
must not occupy the delay slot of another branch or
jump instruction. Since the 'jal' returns to the first
instruction after the delay slot, I would expect the
effect of the 'j' instruction to be cancelled. Or
is this some kind of trick I do not understand?

tk

-- 
--------------------------------------------------

Thomas Koeller, Software Development
Basler Vision Technologies

thomas dot koeller at baslerweb dot com
http://www.baslerweb.com

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