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device/dram/ddr3: Move CRC calculation in a separate function 

Calculating the CRC of a SPD may be useful by itself, so split that
part of the code in a separate function.

Change-Id: I6c20d3db380551865126fd890e89de6b06359207
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-on: http://review.coreboot.org/4537
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
This commit is contained in:
Alexandru Gagniuc 2013-12-17 13:08:01 -05:00
parent d7813436b3
commit 4c37e58ea5
2 changed files with 43 additions and 20 deletions
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62
src/device/dram/ddr3.c
View File

@ -48,6 +48,46 @@ int dimm_is_registered(enum spd_dimm_type type)
return 0;
}
/**
* \brief Calculate the CRC of a DDR3 SPD
*
* @param spd pointer to raw SPD data
* @param len length of data in SPD
*
* @return the CRC of the SPD data, or 0 when spd data is truncated.
*/
u16 spd_ddr3_calc_crc(u8 *spd, int len)
{
int n_crc, i;
u8 *ptr;
u16 crc;
/* Find the number of bytes covered by CRC */
if (spd[0] & 0x80) {
n_crc = 117;
} else {
n_crc = 126;
}
if (len < n_crc)
/* Not enough bytes available to get the CRC */
return 0;
/* Compute the CRC */
crc = 0;
ptr = spd;
while (--n_crc >= 0) {
crc = crc ^ (int)*ptr++ << 8;
for (i = 0; i < 8; ++i)
if (crc & 0x8000) {
crc = crc << 1 ^ 0x1021;
} else {
crc = crc << 1;
}
}
return crc;
}
/**
* \brief Decode the raw SPD data
*
@ -68,9 +108,8 @@ int dimm_is_registered(enum spd_dimm_type type)
*/
int spd_decode_ddr3(dimm_attr * dimm, spd_raw_data spd)
{
int nCRC, i, ret;
int ret;
u16 crc, spd_crc;
u8 *ptr = spd;
u8 ftb_divisor, ftb_dividend, capacity_shift, bus_width, sdram_width;
u8 reg8;
u32 mtb; /* medium time base */
@ -88,24 +127,7 @@ int spd_decode_ddr3(dimm_attr * dimm, spd_raw_data spd)
}
dimm->dram_type = SPD_MEMORY_TYPE_SDRAM_DDR3;
/* Find the number of bytes covered by CRC */
if (spd[0] & 0x80) {
nCRC = 117;
} else {
nCRC = 126;
}
/* Compute the CRC */
crc = 0;
while (--nCRC >= 0) {
crc = crc ^ (int)*ptr++ << 8;
for (i = 0; i < 8; ++i)
if (crc & 0x8000) {
crc = crc << 1 ^ 0x1021;
} else {
crc = crc << 1;
}
}
crc = spd_ddr3_calc_crc(spd, sizeof(spd));
/* Compare with the CRC in the SPD */
spd_crc = (spd[127] << 8) + spd[126];
/* Verify the CRC is correct */

1
src/include/device/dram/ddr3.h
View File

@ -170,6 +170,7 @@ enum spd_status {
typedef u8 spd_raw_data[256];
u16 spd_ddr3_calc_crc(u8 *spd, int len);
int spd_decode_ddr3(dimm_attr * dimm, spd_raw_data spd_data);
int dimm_is_registered(enum spd_dimm_type type);
void dram_print_spd_ddr3(const dimm_attr * dimm);