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patch #922836 by Jens: way faster disk writing, in assembler. The code is in, but yet disabled by #define PREFER_C_WRITING unless it's proven safe for all disks.

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git-svn-id: svn://svn.rockbox.org/rockbox/trunk@4460 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Jörg Hohensohn 2004-04-01 05:46:31 +00:00
parent cbd992b440
commit 9c52b24b00
1 changed files with 126 additions and 13 deletions
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139
firmware/drivers/ata.c
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@ -32,6 +32,8 @@
/* use plain C code in copy_read_sectors(), instead of tweaked assembler */
#define PREFER_C /* mystery: assembler caused problems with some disks */
/* use plain C code in copy_write_sectors(), instead of tweaked assembler */
#define PREFER_C_WRITING /* we don't know yet about this one */
#define SECTOR_SIZE 512
#define ATA_DATA (*((volatile unsigned short*)0x06104100))
@ -208,11 +210,9 @@ static void copy_read_sectors(unsigned char* buf, int wordcount)
"tst #1,r0 \n" /* 16-bit aligned ? */
"bt .aligned \n" /* yes, do word copy */
".align 2 \n"
/* not 16-bit aligned */
"mov #-1,r3 \n" /* prepare a bit mask for high byte */
"extu.b r3,r3 \n"
"swap.b r3,r3 \n" /* r3 = 0x0000FF00 */
"shll8 r3 \n" /* r3 = 0xFFFFFF00 */
"mov.w @%2,r2 \n" /* read first word (1st round) */
"add #-12,%1 \n" /* adjust end address for offsets */
@ -220,6 +220,7 @@ static void copy_read_sectors(unsigned char* buf, int wordcount)
"bra .start4_b \n" /* jump into loop after next instr. */
"add #-5,%0 \n" /* adjust for dest. offsets; now even */
".align 2 \n"
".loop4_b: \n" /* main loop: copy 4 words in a row */
"mov.w @%2,r2 \n" /* read first word (2+ round) */
"and r3,r1 \n" /* get high byte of fourth word (2+ round) */
@ -250,10 +251,8 @@ static void copy_read_sectors(unsigned char* buf, int wordcount)
/* avg. 6.5 cycles per word - 100% faster */
"swap.b r1,r0 \n" /* get high byte of last word */
"mov.b r0,@(4,%0) \n" /* and store it */
"bra .exit \n"
"nop \n"
"mov.b r0,@(4,%0) \n" /* and store it */
".align 2 \n"
/* 16-bit aligned, loop(read and store word) */
@ -287,7 +286,7 @@ static void copy_read_sectors(unsigned char* buf, int wordcount)
"swap.b r1,r0 \n" /* swap fourth word (last round) */
"mov.w r0,@(4,%0) \n" /* and store it */
".exit: \n"
".exit: \n"
: /* outputs */
: /* inputs */
/* %0 */ "r"(buf),
@ -447,6 +446,124 @@ int ata_read_sectors(unsigned long start,
return ret;
}
/* the tight loop of ata_write_sectors(), to avoid the whole in IRAM */
static void copy_write_sectors(unsigned char* buf,
int wordcount)
__attribute__ ((section (".icode")));
static void copy_write_sectors(unsigned char* buf, int wordcount)
{
#ifdef PREFER_C_WRITING
if ( (unsigned int)buf & 1)
{ /* not 16-bit aligned, copy byte by byte */
unsigned short tmp = 0;
unsigned char* bufend = buf + wordcount*2;
do
{ /* loop compiles to 8 assembler instructions */
/* takes 12 clock cycles because of 2 pipeline stalls */
tmp = (unsigned short) *buf++;
tmp |= (unsigned short) *buf++ << 8; /* I assume big endian */
ATA_DATA = tmp; /* and don't use the SWAB16 macro */
} while (buf < bufend); /* tail loop is faster */
}
else
{ /* 16-bit aligned, can do faster copy */
unsigned short* wbuf = (unsigned short*)buf;
unsigned short* wbufend = wbuf + wordcount;
do
{ /* loop compiles to 5 assembler instructions */
/* takes 9 clock cycles because of 2 pipeline stalls */
ATA_DATA = SWAB16(*wbuf);
} while (++wbuf < wbufend); /* tail loop is faster */
}
#else
/* optimized assembler version */
/* this assumes wordcount to be a multiple of 2 */
/* writing is not unrolled as much as reading, for several reasons:
* - a similar instruction sequence is faster for writing than for reading
* because the auto-incrementing load inctructions can be used
* - writing profits from warp mode
* Both of these add up to have writing faster than the more unrolled reading.
*/
asm (
"add %1,%1 \n" /* wordcount -> bytecount */
"add %0,%1 \n" /* bytecount -> bufend */
"mov %0,r0 \n"
"tst #1,r0 \n" /* 16-bit aligned ? */
"bt .w_aligned \n" /* yes, do word copy */
/* not 16-bit aligned */
"mov #-1,r6 \n" /* prepare a bit mask for high byte */
"shll8 r6 \n" /* r6 = 0xFFFFFF00 */
"mov.b @%0+,r2 \n" /* load (initial old second) first byte */
"add #-4,%1 \n" /* adjust end address for early check */
"mov.w @%0+,r3 \n" /* load (initial) first word */
"bra .w_start2_b \n"
"extu.b r2,r0 \n" /* extend unsigned */
".align 2 \n"
".w_loop2_b: \n" /* main loop: copy 2 words in a row */
"mov.w @%0+,r3 \n" /* load first word (2+ round) */
"extu.b r2,r0 \n" /* put away low byte of second word (2+ round) */
"and r6,r2 \n" /* get high byte of second word (2+ round) */
"or r1,r2 \n" /* combine with low byte of old first word */
"mov.w r2,@%2 \n" /* write that */
".w_start2_b: \n"
"cmp/hi %0,%1 \n" /* check for end */
"mov.w @%0+,r2 \n" /* load second word */
"extu.b r3,r1 \n" /* put away low byte of first word */
"and r6,r3 \n" /* get high byte of first word */
"or r0,r3 \n" /* combine with high byte of old second word */
"mov.w r3,@%2 \n" /* write that */
"bt .w_loop2_b \n"
/* 12 instructions for 2 copies, takes 14 clock cycles */
/* avg. 7 cycles per word - 71% faster */
/* the loop "overreads" 1 byte past the buffer end, however, the last */
/* byte is not written to disk */
"and r6,r2 \n" /* get high byte of last word */
"or r1,r2 \n" /* combine with low byte of old first word */
"bra .w_exit \n"
"mov.w r2,@%2 \n" /* write last word */
/* 16-bit aligned, loop(load and write word) */
".w_aligned: \n"
"mov.w @%0+,r2 \n" /* load first word (1st round) */
"bra .w_start2_w \n" /* jump into loop after next instr. */
"add #-4,%1 \n" /* adjust end address for early check */
".align 2 \n"
".w_loop2_w: \n" /* main loop: copy 2 words in a row */
"mov.w @%0+,r2 \n" /* load first word (2+ round) */
"swap.b r1,r0 \n" /* swap second word (2+ round) */
"mov.w r0,@%2 \n" /* write second word (2+ round) */
".w_start2_w: \n"
"cmp/hi %0,%1 \n" /* check for end */
"mov.w @%0+,r1 \n" /* load second word */
"swap.b r2,r0 \n" /* swap first word */
"mov.w r0,@%2 \n" /* write first word */
"bt .w_loop2_w \n"
/* 8 instructions for 2 copies, takes 10 clock cycles */
/* avg. 5 cycles per word - 80% faster */
"swap.b r1,r0 \n" /* swap second word (last round) */
"mov.w r0,@%2 \n" /* and write it */
".w_exit: \n"
: /* outputs */
: /* inputs */
/* %0 */ "r"(buf),
/* %1 */ "r"(wordcount),
/* %2 */ "r"(&ATA_DATA)
: /*trashed */
"r0","r1","r2","r3","r6"
);
#endif
}
int ata_write_sectors(unsigned long start,
int count,
void* buf)
@ -502,7 +619,7 @@ int ata_write_sectors(unsigned long start,
ATA_COMMAND = CMD_WRITE_SECTORS;
for (i=0; i<count; i++) {
int j;
if (!wait_for_start_of_transfer()) {
ret = -3;
break;
@ -515,11 +632,7 @@ int ata_write_sectors(unsigned long start,
poweroff = false;
}
for (j=0; j<SECTOR_SIZE/2; j++) {
ATA_DATA = (unsigned short)
(((unsigned char *)buf)[j*2+1] << 8) |
((unsigned char *)buf)[j*2];
}
copy_write_sectors(buf, SECTOR_SIZE/2);
#ifdef USE_INTERRUPT
/* reading the status register clears the interrupt */