Date: Tue, 15 Jul 2003 13:54:14 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: Nate Lawson <nate@root.org> Cc: imp@bsdimp.com Subject: Re: newbus questions Message-ID: <20030715133552.F10662@gamplex.bde.org> In-Reply-To: <20030714173017.F18544@root.org> References: <20030714173017.F18544@root.org>
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On Mon, 14 Jul 2003, Nate Lawson wrote: > 3. It appears bus_alloc_resource() takes a range of values. If I know the > exact value to use, I request it via "value, value" instead of "0, ~0". > Is this correct? It's correct if you really know the values, unlike "0, ~0". The maximum value for a resource is ULONG_MAX. This is also a magic value in conjunction with a value of 0 for the start of a resource and a value of 1 for the count (see the man page). ULONG_MAX can be spelled ~0ul to abbreviate and obfuscate the code a little. ULONG_MAX can't be spelled ~0, but this is what the man page description says to use for the magic value. ~0 is -1 on 2's complement machines and -0 on 1's complement machines. It just happens to become ULONG_MAX on some machines including 2's complement ones after bogus type conversions when it is passed to bus_alloc_resource. Most drivers use the bogus version of course. The examples in the man page are correct although the description isn't. Bruce
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