Date: Wed, 18 Nov 1998 09:36:42 +1030 (CST) From: Mark Newton <newton@atdot.dotat.org> To: paipai@tin.it (Paolo Di Francesco) Cc: freebsd-sparc@FreeBSD.ORG Subject: Re: Porting process (Again) Message-ID: <199811172306.JAA00931@atdot.dotat.org> In-Reply-To: <19981117191824.ELKO23830.fep03-svc@winworkstation> from "Paolo Di Francesco" at Nov 17, 98 08:19:59 pm
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Paolo Di Francesco wrote:
> Step #1) Read docs about the booting process, and do experiments on it.
> This means we need to write some asm code and do some unusefull things,
> such as to print on the screen "Hello world". I can do it on i386 using
> a floppy. This mean I can boot ANYTHING from the floppy. (Well, I loaded
> an image directly from the boot sector). The same thing will happen
> under Sparc.
> This will improve the asm skill...
NetBSD's /sys/arch/sparc/stand probably has everything you need. Indeed,
"borrowing" their bootblocks and standalone code verbatim might be possible.
> Step #2) Choose a version to start from. (Maybe 3.0?)
Absolutely: 3.0-CURRENT. You don't want the port to be obselete before
it even starts.
> Step #3) Isolate the asm (i386) code from the FreeBSD kernel code. This
> mean :
> Step #3.1) Isolate the asm directory and then the asm source files. Many
> of the directories have no asm code, so we need concentrate on the dirs
> which HAVE asm code. Then, in these dirs many files have no asm code.
> And so on. So a document with a tree like
[ yada yada ]
/sys/i386/i386 should be the only relevent directory which asm code in
it (there is also some in /sys/i386/isa, /sys/i386/boot and /sys/i386/linux,
yes, but you aren't going to have a SPARC box with an ISA bus or i386
bootblocks, are you?).
Some (most?) of the asm code in /sys/i386/i386 is only assembly language
for speed, and could just as easily be written in C (indeed, some of it
used to be C, from memory: bcopy routines spring immediately to mind).
There's also a small amount of assembly-that-could-be-C in
/usr/src/lib/libc/i386, but you aren't worried about userland yet anyway,
right? Oh, I guess you'll want to port the system call stub routine --
Grab NetBSD's.
> Step #3.2) Understand priority. What we need NOW to boot... For example
> we do not need "low priority" files which are not usefull for the first
> kernel version.
Probably the easiest config for initial testing is something which
includes the basic kernel, a PROM console device driver (no framebuffers
or anything) and a PROM polled ethernet driver. With that config you can
use an NFS root filesystem, so you won't have to write/debug any SCSI
device drivers to get things up and running (if you use interfaces to
the PROM devices you won't have to write any hardware-knowledgable
device drivers at all. If you're polling ethernet/console you won't
even need to care if your embryonic interrupt system is slightly broken).
> Step #4) configure the base kernel and compile it under i386.
Natch. Port the toolchain to run on NetBSD/sparc (or NetBSD/sparc64)
and develop there. Cross compilation on an i386 isn't necessarily a win.
> Step #n-1) Write the device dependent code. Controller, network cards, misc
> cards, and so on.
Probably start with a hardware-knowledgable ethernet driver to replace
the (high-overhead) PROM driver, then do SCSI, then take it from there.
On the uSPARC a lot of the PCI drivers have already been written for you;
You'd just need PCI glue code. The new bus abstraction being worked on
for FreeBSD-current might help a lot here too.
- mark
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I tried an internal modem, newton@atdot.dotat.org
but it hurt when I walked. Mark Newton
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