From: Julius Baxter <juliusbaxter@gmail.com>
To: cgen@sourceware.org
Subject: Re: Delay slots in GNU sim
Date: Mon, 16 Jan 2012 07:50:00 -0000 [thread overview]
Message-ID: <CAF6YiZ474rnjXWED6DvuZ=A-f-YtfXyma-ZikPktveKvJ=eZrw@mail.gmail.com> (raw)
In-Reply-To: <CAF6YiZ673yCz5CxbA3+cVn_snt0q58Ta_gQLtJCm-bjADf6Vdg@mail.gmail.com>
On Sun, Jan 15, 2012 at 2:24 PM, Julius Baxter <juliusbaxter@gmail.com> wrote:
> Hi,
>
> I've been working on the OpenRISC CGEN description and have got the
> assembler working and am now looking at getting a GNU sim port running
> too.
>
> I can see a lot of functionality working OK so far (I've based my
> simulator port on the lm32 and m32r ports, which are both CGEN-based
> implementations of the simulator) but one thing which is not working
> are delay slots. They never appear to b executed when a branch is
> going to be taken.
>
> I'm yet to delve into the workings if the simulator to figure out why
> it's not executing the delay slots, but I just wanted to ask if this
> is a known issue with the particular configuration I'm using. The sim
> port has "#define WITH_SCACHE_PBB 1", in the tconfig.in file and the
> Makefile calls the mloop.c generation script with:
>
> ...
> $(SHELL) $(srccom)/genmloop.sh \
> -mono -fast -pbb -full-switch -switch sem-switch.c \
> -cpu or1k32bef -infile $(srcdir)/mloop.in
>
> ...
>
> My understanding is that this will generate a main loop for a "fast"
> model with pseudo-basic-block processing. This is an "upgrade" over
> the default "simple" model without pbb.
>
> I'm wondering if delay slots not working are a known issue when
> compiling a fast model with pbb support?
>
> As far as I can tell, my semantic description is correct. For example,
> the jump instruction is:
>
> (dni l-j "jump (pc-relative iaddr)"
> ; This function may not be in delay slot
> (NOT-IN-DELAY-SLOT)
>
> "l.j ${disp-26}"
> (+ OPC_J disp-26)
>
> ; We execute the delay slot before doin' the real branch
> (delay 1 (set pc disp-26))
> ()
> )
>
> Other semantic descriptions of delay slot execution appear to be along
> the same lines, but I can't see any CGEN-based sim ports which have
> instructions with delay slots, so, as I said, I'm wondering if this is
> even supported at all.
I didn't look hard enough, the cris and iq2000 sim ports implement
instructions using delay slots.
I fixed this issue after looking at their mloop.in files and realised
I was missing a section to handle delay slots. With this code added it
looks like delay slot instructions are getting executed.
Cheers
Julius
prev parent reply other threads:[~2012-01-16 7:50 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-15 3:25 Julius Baxter
2012-01-16 7:50 ` Julius Baxter [this message]
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