262e0a636b
The time base conversion factor is the 32 bit value 2^32 * 1000000 / time base frequency, so the system time can be computed by system time = time base * conversion factor / 2^32. The expression in system_time() looks more complicated now, but is actually much faster (factor 2.5 on my Mac mini). I'm positively surprised, how good the assembly looks, that GCC 4 generates. There's not that much potential for optimization by hand-coding the function. git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@15863 a95241bf-73f2-0310-859d-f6bbb57e9c96
37 lines
1.4 KiB
C
37 lines
1.4 KiB
C
/*
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* Copyright 2006, Ingo Weinhold <bonefish@cs.tu-berlin.de>.
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* All rights reserved. Distributed under the terms of the MIT License.
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*/
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#ifndef _KERNEL_ARCH_REAL_TIME_DATA_H
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#define _KERNEL_ARCH_REAL_TIME_DATA_H
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#include <StorageDefs.h>
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#include <SupportDefs.h>
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struct ppc_real_time_data {
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vint64 system_time_offset;
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};
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struct arch_real_time_data {
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struct ppc_real_time_data data[2];
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vint32 system_time_conversion_factor;
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vint32 version;
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// Since there're no cheap atomic_{set,get,add}64() on PPC 32 (i.e. one
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// that doesn't involve a syscall), we can't have just a single
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// system_time_offset and set/get it atomically.
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// That's why have our data twice. One set is current (indexed by
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// version % 2). When setting the offset, we do that with disabled
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// interrupts and protected by a spinlock. We write the new values
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// into the other array element and increment the version.
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// A reader first reads the version, then the date of interest, and
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// finally rechecks the version. If it hasn't changed in the meantime,
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// the read value is fine, otherwise it runs the whole procedure again.
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//
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// system_time_conversion_factor is currently consider constant,
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// although that is not necessarily true. We simply don't support
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// changing conversion factors at the moment.
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};
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#endif /* _KERNEL_ARCH_REAL_TIME_DATA_H */
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