The problem were all minor - as somepne pointed out, that "I" constraint
should have been "i" and I forgot a set of parens somewhere they were
syntactically required.
I'm currently posting from a 2.1.126pre2 kernel with my "large" patch
installed and compiled with egcc -O3 -march=pentium -fomit-frame-pointer.
gcc version egcs-2.91.34 19980531 (gcc2 ss-980502 experimental)
The clock seems to tick at approximately the correct rate, and in the hour
the machine has been up, NTP seems fairly happy with it.
I inepcted the code produced from gcc -O2, egcc -O2 and egcc -O3,
and it all looks good.
-- -ColinThe "minimal" patch. This compiles correctly. --- time.c Sun Oct 18 08:17:30 1998 +++ time.c Sun Oct 18 08:21:55 1998 @@ -563,12 +563,11 @@ "movl %%eax, %%ecx\n\t" "xorl %%eax, %%eax\n\t" "movl %1, %%edx\n\t" - "divl %%ecx\n\t" /* eax= 2^32 / (1 * TSC counts per microsecond) */ + "divl %%ecx" /* eax= 2^32 / (1 * TSC counts per microsecond) */ /* Return eax for the use of fast_gettimeoffset */ - "movl %%eax, %0\n\t" - : "=r" (retval) - : "r" (5 * 1000020/HZ) - : /* we clobber: */ "ax", "bx", "cx", "dx", "cc", "memory"); + : "=&a" (retval) + : "i" (5 * 1000020/HZ) + : /* we clobber: */ "bx", "cx", "dx", "cc", "memory"); return retval; } The "large" patch. More changes, but a cleaner (IMHO) result. --- time.c Sun Oct 18 08:17:30 1998 +++ time.c Tue Oct 20 12:50:57 1998 @@ -508,68 +508,84 @@ __initfunc(static unsigned long calibrate_tsc(void)) { - unsigned long retval; + unsigned long retval; + unsigned long before, after; + unsigned long edx; /* Dummy variable */ + unsigned long long scaled_us; - __asm__( /* set the Gate high, program CTC channel 2 for mode 0 + __asm__(/* set the Gate high, program CTC channel 2 for mode 0 * (interrupt on terminal count mode), binary count, * load 5 * LATCH count, (LSB and MSB) * to begin countdown, read the TSC and busy wait. - * BTW LATCH is calculated in timex.h from the HZ value + * BTW LATCH is calculated in timex.h from the HZ value, + * and 5*LATCH is the most that will fit into 16 bits. */ - /* Set the Gate high, disable speaker */ - "inb $0x61, %%al\n\t" /* Read port */ - "andb $0xfd, %%al\n\t" /* Turn off speaker Data */ - "orb $0x01, %%al\n\t" /* Set Gate high */ - "outb %%al, $0x61\n\t" /* Write port */ - - /* Now let's take care of CTC channel 2 */ - "movb $0xb0, %%al\n\t" /* binary, mode 0, LSB/MSB, ch 2*/ - "outb %%al, $0x43\n\t" /* Write to CTC command port */ - "movb $0x0c, %%al\n\t" - "outb %%al, $0x42\n\t" /* LSB of count */ - "movb $0xe9, %%al\n\t" - "outb %%al, $0x42\n\t" /* MSB of count */ - - /* Read the TSC; counting has just started */ - "rdtsc\n\t" - /* Move the value for safe-keeping. */ - "movl %%eax, %%ebx\n\t" - "movl %%edx, %%ecx\n\t" - - /* Busy wait. Only 50 ms wasted at boot time. */ - "0: inb $0x61, %%al\n\t" /* Read Speaker Output Port */ - "testb $0x20, %%al\n\t" /* Check CTC channel 2 output (bit 5) */ - "jz 0b\n\t" - - /* And read the TSC. 5 jiffies (50.00077ms) have elapsed. */ - "rdtsc\n\t" - - /* Great. So far so good. Store last TSC reading in - * last_tsc_low (only 32 lsb bits needed) */ - "movl %%eax, last_tsc_low\n\t" - /* And now calculate the difference between the readings. */ - "subl %%ebx, %%eax\n\t" - "sbbl %%ecx, %%edx\n\t" /* 64-bit subtract */ - /* but probably edx = 0 at this point (see below). */ - /* Now we have 5 * (TSC counts per jiffy) in eax. We want - * to calculate TSC->microsecond conversion factor. */ - - /* Note that edx (high 32-bits of difference) will now be - * zero iff CPU clock speed is less than 85 GHz. Moore's - * law says that this is likely to be true for the next - * 12 years or so. You will have to change this code to - * do a real 64-by-64 divide before that time's up. */ - "movl %%eax, %%ecx\n\t" - "xorl %%eax, %%eax\n\t" - "movl %1, %%edx\n\t" - "divl %%ecx\n\t" /* eax= 2^32 / (1 * TSC counts per microsecond) */ - /* Return eax for the use of fast_gettimeoffset */ - "movl %%eax, %0\n\t" - : "=r" (retval) - : "r" (5 * 1000020/HZ) - : /* we clobber: */ "ax", "bx", "cx", "dx", "cc", "memory"); - return retval; + /* Set the Gate high, disable speaker */ + "inb $0x61, %%al\n\t" /* Read port */ + "andb $0xfd, %%al\n\t" /* Turn off speaker Data */ + "orb $0x01, %%al\n\t" /* Set Gate high */ + "outb %%al, $0x61\n\t" /* Write port */ + + /* Now let's take care of CTC channel 2 */ + "movb $0xb0, %%al\n\t" /* binary, mode 0, LSB/MSB, ch 2*/ + "outb %%al, $0x43\n\t" /* Write to CTC command port */ + "movb %3, %%al\n\t" + "outb %%al, $0x42\n\t" /* LSB of count */ + "movb %4, %%al\n\t" + "outb %%al, $0x42\n\t" /* MSB of count */ + + /* Read the TSC; counting has just started */ + "rdtsc\n\t" + /* Remeber the value for later (only 32 bits - see below) */ + "movl %%eax, %0\n" + + /* Busy wait. Only 50 ms wasted at boot time. */ + "0:\tinb $0x61, %%al\n\t" /* Read Speaker Output Port */ + "testb $0x20, %%al\n\t" /* Check CTC channel 2 output (bit 5) */ + "jz 0b\n\t" + + /* And read the TSC. 5 jiffies (50.00077ms) have elapsed. */ + "rdtsc" + : "=r" (before), "=&a" (after), "=d" (edx) + : "g" ((unsigned char)(5*LATCH)), + "g" ((unsigned char)(5*LATCH/256)) + : "cc"); + /* + * We only return 32 bits because the difference will fit as long + * as the CPU clock speed is less than 85 GHz. Moore's law says + * that this is likely to be true for the next 12 years or so. + * You will have to change this code to do a real 64-by-64 divide + * before that time's up. + */ + + /* Store last TSC reading in last_tsc_low (only 32 bits needed) */ + last_tsc_low = after; + + /* + * We want here 2^32 * elapsed microseconds, i.e. + * 2^32 * 5 * LATCH * (1000000/CLOCK_TICK_RATE). This can be + * computed to full precision if we use CLOCK_TICK_FACTOR, a factor + * of both 1000000 and CLOCK_TICK_RATE to reduce the size of the + * numbers so the numerator (barely!) fits into 64 bits. + * (It's B1CCF7C0 00000000) + */ + scaled_us = 5u*LATCH*(1000000/CLOCK_TICK_FACTOR) * (1ull<<32) / + (CLOCK_TICK_RATE/CLOCK_TICK_FACTOR); + + /* + * 64/32-bit divide to compute TSC->microseconds conversion factor. + * (GCC does it inefficiently, ugh, because it doesn't know the + * result won't overflow.) + */ + __asm__ ( + "divl %2" + : "=a" (retval), "=d" (edx) + : "g" (after-before), "a" ((unsigned)scaled_us), + "d" ((unsigned)(scaled_us>>32)) + : "cc"); + + return retval; } __initfunc(void time_init(void))
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