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Optimized the sector read loop as much as C allows. I measured an overall speed improvement for file reading of 12.5% for 16-bit aligned and 35% for misaligned. I took the rest of ata_read_sectors() out of IRAM, it's sufficient if only the copy loop stays there.

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git-svn-id: svn://svn.rockbox.org/rockbox/trunk@4247 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Jörg Hohensohn 2004-01-16 09:02:21 +00:00
parent 89d2039367
commit 88faf38ef7
1 changed files with 34 additions and 15 deletions
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49
firmware/drivers/ata.c
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@ -161,9 +161,39 @@ static int wait_for_end_of_transfer(void)
return (ATA_ALT_STATUS & (STATUS_RDY|STATUS_DRQ)) == STATUS_RDY;
}
int ata_read_sectors(unsigned long start,
int count,
void* buf) __attribute__ ((section (".icode")));
/* the tight loop of ata_read_sectors(), to avoid the whole in IRAM */
static void copy_read_sectors(unsigned char* buf,
int wordcount)
__attribute__ ((section (".icode")));
static void copy_read_sectors(unsigned char* buf, int wordcount)
{
int j;
if (wordcount <= 0)
return; /* should never happen, but to protect my tail loop */
if ( (unsigned int)buf & 1 )
{
unsigned char* bufend = buf + wordcount*2;
do
{ /* loop compiles to 8 assembler instructions */
unsigned short tmp = ATA_DATA;
*buf++ = tmp & 0xff; /* I assume big endian */
*buf++ = tmp >> 8; /* and don't use the SWAB16 macro */
} while (buf < bufend); /* tail loop is faster */
}
else
{
unsigned short* wbuf = (unsigned short*)buf;
unsigned short* wbufend = wbuf + wordcount;
do
{ /* loop compiles to 7 assembler instructions */
*wbuf = SWAB16(ATA_DATA);
} while (++wbuf < wbufend); /* tail loop is faster */
}
}
int ata_read_sectors(unsigned long start,
int incount,
void* inbuf)
@ -235,7 +265,6 @@ int ata_read_sectors(unsigned long start,
asm volatile ("nop");
while (count) {
int j;
int sectors;
int wordcount;
int status;
@ -265,17 +294,7 @@ int ata_read_sectors(unsigned long start,
wordcount = sectors * SECTOR_SIZE / 2;
if ( (unsigned int)buf & 1 ) {
for (j=0; j < wordcount; j++) {
unsigned short tmp = SWAB16(ATA_DATA);
((unsigned char*)buf)[j*2] = tmp >> 8;
((unsigned char*)buf)[j*2+1] = tmp & 0xff;
}
}
else {
for (j=0; j < wordcount; j++)
((unsigned short*)buf)[j] = SWAB16(ATA_DATA);
}
copy_read_sectors(buf, wordcount);
/*
"Device errors encountered during READ MULTIPLE commands are