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Fix to check for RDTSC instruction (above 486), and call another timing

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function instead if RDTSC is unavailable. This makes minix run on 486
again :) (presumably lower as well).
This commit is contained in:
Ben Gras 2005-07-01 09:39:47 +00:00
parent d2018bb8ad
commit 2ce80ece5c
1 changed files with 15 additions and 1 deletions
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16
kernel/system.c
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@ -243,7 +243,21 @@ PUBLIC void get_randomness()
* the lowest bytes because the highest bytes won't differ that much.
*/
unsigned long tsc_high;
read_tsc(&tsc_high, &krandom.r_buf[krandom.r_next]);
/* On machines with the RDTSC (cycle counter read instruction - pentium
* and up), use that for high-resolution raw entropy gathering. Otherwise,
* use the realtime clock (tick resolution).
*
* Unfortunately this test is run-time - we don't want to bother with
* compiling different kernels for different machines..
*
* On machines without RDTSC, we use the get_uptime() - read_clock()
* has a higher resolution, but would involve I/O calls.
*/
if(machine.processor > 486)
read_tsc(&tsc_high, &krandom.r_buf[krandom.r_next]);
else
krandom.r_buf[krandom.r_next] = get_uptime();
if (krandom.r_size < RANDOM_ELEMENTS) krandom.r_size ++;
krandom.r_next = (krandom.r_next + 1 ) % RANDOM_ELEMENTS;
}