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Assembly code for copy_read_sectors() reworked: I've spread the ATA reads apart by filling independent instructions inbetween, this is also slightly faster because of no pipeline stall. Hopefully this fixes the problem Kargatron had with it.

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git-svn-id: svn://svn.rockbox.org/rockbox/trunk@4302 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Jörg Hohensohn 2004-02-09 08:24:25 +00:00
parent 06500c84ce
commit b646d4f278
1 changed files with 39 additions and 20 deletions
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59
firmware/drivers/ata.c
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@ -181,16 +181,23 @@ static void copy_read_sectors(unsigned char* buf, int wordcount)
*buf++ = tmp >> 8; /* and don't use the SWAB16 macro */
} while (buf < bufend); /* tail loop is faster */
#else
asm ( /* I can bring it down to 7 instructions/loop */
"mov #1, r0 \n"
/* I can bring it down to 7 instructions/loop, and exploit pipeline */
asm (
"mov #1, r0 \n" /* r0 = 1; */
/* correct for the "early increment" below */
"add #-2,%2 \n" /* buf -= 2; */
"add #-2,%3 \n" /* bufend -= 2; */
"loop_b: \n"
"mov.w @%1,%0 \n"
"mov.b %0,@%2 \n"
"shlr8 %0 \n"
"mov.b %0,@(r0,%2) \n"
"add #0x02,%2 \n"
"cmp/hs %3,%2 \n"
"bf loop_b \n"
"mov.w @%1,%0 \n" /* tmp = ATA_DATA; */
/* Now we're reading from the bus, I do something independent we
need later, to avoid pipeline stall */
"add #0x02,%2 \n" /* buf += 2; */
"cmp/hs %3,%2 \n" /* if (buf < bufend) */
/* now use the read result */
"mov.b %0,@%2 \n" /* buf[0] = lowbyte(tmp); */
"shlr8 %0 \n" /* tmp >>= 8; */
"mov.b %0,@(r0,%2) \n" /* buf[r0] = lowbyte(tmp); */
"bf loop_b \n" /* goto loop_b; */
: /* outputs */
: /* inputs */
/* %0 */ "r"(tmp),
@ -212,18 +219,30 @@ static void copy_read_sectors(unsigned char* buf, int wordcount)
*wbuf = SWAB16(ATA_DATA);
} while (++wbuf < wbufend); /* tail loop is faster */
#else
asm ( /* I can bring it down to 9 instructions for 2 loops */
"mov #2, r0 \n"
/* I can bring it down to 9 instructions for 2 loops, and pipeline */
asm (
"mov #2, r0 \n" /* r0 = 2 */
/* correct for the "early increment" below */
"add #-4,%2 \n" /* wbuf -= 4; */
"bra enter_loop \n" /* goto enter_loop, after next instr. */
"add #-4,%3 \n" /* wbufend -= 4; */
"loop_w: \n"
"mov.w @%1,%0 \n"
"swap.b %0,%0 \n"
"mov.w %0,@%2 \n"
"mov.w @%1,%0 \n" /* unrolled, do one more */
"swap.b %0,%0 \n"
"mov.w %0,@(r0,%2) \n"
"add #0x04,%2 \n"
"cmp/hs %3,%2 \n"
"bf loop_w \n"
/* use read result and store, from last round */
"swap.b %0,%0 \n" /* endian_swap(tmp); */
"mov.w %0,@(r0,%2) \n" /* wbuf[r0] = tmp; */
"enter_loop: \n"
"mov.w @%1,%0 \n" /* tmp = ATA_DATA; */
/* keep the pipeline busy with 2 independent instructions */
"add #0x04,%2 \n" /* wbuf += 4; */
"cmp/hs %3,%2 \n" /* if (wbuf < wbufend) */
"swap.b %0,%0 \n" /* endian_swap(tmp); */
"mov.w %0,@%2 \n" /* wbuf[0] = tmp; */
/* unrolled, do one more */
"mov.w @%1,%0 \n" /* tmp = ATA_DATA; */
/* use and store later, to keep pipeline busy */
"bf loop_w \n" /* goto loop_w; */
"swap.b %0,%0 \n" /* endian_swap(tmp); */
"mov.w %0,@(r0,%2) \n" /* wbuf[r0] = tmp; */
: /* outputs */
: /* inputs */
/* %0 */ "r"(tmp),