upstream u-boot with additional patches for our devices/boards: https://lists.denx.de/pipermail/u-boot/2017-March/282789.html (AXP crashes) ; Gbit ethernet patch for some LIME2 revisions ; with SPI flash support
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u-boot/board/lwmon5/sdram.c

648 lines
17 KiB

/*
* (C) Copyright 2006
* Sylvie Gohl, AMCC/IBM, gohl.sylvie@fr.ibm.com
* Jacqueline Pira-Ferriol, AMCC/IBM, jpira-ferriol@fr.ibm.com
* Thierry Roman, AMCC/IBM, thierry_roman@fr.ibm.com
* Alain Saurel, AMCC/IBM, alain.saurel@fr.ibm.com
* Robert Snyder, AMCC/IBM, rob.snyder@fr.ibm.com
*
* (C) Copyright 2007
* Stefan Roese, DENX Software Engineering, sr@denx.de.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of
* the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston,
* MA 02111-1307 USA
*/
/* define DEBUG for debugging output (obviously ;-)) */
#if 0
#define DEBUG
#endif
#include <common.h>
#include <asm/processor.h>
#include <asm/mmu.h>
#include <asm/io.h>
#include <ppc440.h>
#include "sdram.h"
/*
* This DDR2 setup code can dynamically setup the TLB entries for the DDR2 memory
* region. Right now the cache should still be disabled in U-Boot because of the
* EMAC driver, that need it's buffer descriptor to be located in non cached
* memory.
*
* If at some time this restriction doesn't apply anymore, just define
* CFG_ENABLE_SDRAM_CACHE in the board config file and this code should setup
* everything correctly.
*/
#ifdef CFG_ENABLE_SDRAM_CACHE
#define MY_TLB_WORD2_I_ENABLE 0 /* enable caching on SDRAM */
#else
#define MY_TLB_WORD2_I_ENABLE TLB_WORD2_I_ENABLE /* disable caching on SDRAM */
#endif
void dcbz_area(u32 start_address, u32 num_bytes);
void dflush(void);
static u32 is_ecc_enabled(void)
{
u32 val;
mfsdram(DDR0_22, val);
val &= DDR0_22_CTRL_RAW_MASK;
if (val)
return 1;
else
return 0;
}
void board_add_ram_info(int use_default)
{
PPC440_SYS_INFO board_cfg;
u32 val;
if (is_ecc_enabled())
puts(" (ECC");
else
puts(" (ECC not");
get_sys_info(&board_cfg);
printf(" enabled, %d MHz", (board_cfg.freqPLB * 2) / 1000000);
mfsdram(DDR0_03, val);
val = DDR0_03_CASLAT_DECODE(val);
printf(", CL%d)", val);
}
static int wait_for_dlllock(void)
{
u32 val;
int wait = 0;
/*
* Wait for the DCC master delay line to finish calibration
*/
mtdcr(ddrcfga, DDR0_17);
val = DDR0_17_DLLLOCKREG_UNLOCKED;
while (wait != 0xffff) {
val = mfdcr(ddrcfgd);
if ((val & DDR0_17_DLLLOCKREG_MASK) == DDR0_17_DLLLOCKREG_LOCKED)
/* dlllockreg bit on */
return 0;
else
wait++;
}
debug("0x%04x: DDR0_17 Value (dlllockreg bit): 0x%08x\n", wait, val);
debug("Waiting for dlllockreg bit to raise\n");
return -1;
}
#if defined(CONFIG_DDR_DATA_EYE)
int wait_for_dram_init_complete(void)
{
u32 val;
int wait = 0;
/*
* Wait for 'DRAM initialization complete' bit in status register
*/
mtdcr(ddrcfga, DDR0_00);
while (wait != 0xffff) {
val = mfdcr(ddrcfgd);
if ((val & DDR0_00_INT_STATUS_BIT6) == DDR0_00_INT_STATUS_BIT6)
/* 'DRAM initialization complete' bit */
return 0;
else
wait++;
}
debug("DRAM initialization complete bit in status register did not rise\n");
return -1;
}
#define NUM_TRIES 64
#define NUM_READS 10
void denali_core_search_data_eye(u32 start_addr, u32 memory_size)
{
int k, j;
u32 val;
u32 wr_dqs_shift, dqs_out_shift, dll_dqs_delay_X;
u32 max_passing_cases = 0, wr_dqs_shift_with_max_passing_cases = 0;
u32 passing_cases = 0, dll_dqs_delay_X_sw_val = 0;
u32 dll_dqs_delay_X_start_window = 0, dll_dqs_delay_X_end_window = 0;
volatile u32 *ram_pointer;
u32 test[NUM_TRIES] = {
0x00000000, 0x00000000, 0xFFFFFFFF, 0xFFFFFFFF,
0x00000000, 0x00000000, 0xFFFFFFFF, 0xFFFFFFFF,
0xFFFFFFFF, 0xFFFFFFFF, 0x00000000, 0x00000000,
0xFFFFFFFF, 0xFFFFFFFF, 0x00000000, 0x00000000,
0xAAAAAAAA, 0xAAAAAAAA, 0x55555555, 0x55555555,
0xAAAAAAAA, 0xAAAAAAAA, 0x55555555, 0x55555555,
0x55555555, 0x55555555, 0xAAAAAAAA, 0xAAAAAAAA,
0x55555555, 0x55555555, 0xAAAAAAAA, 0xAAAAAAAA,
0xA5A5A5A5, 0xA5A5A5A5, 0x5A5A5A5A, 0x5A5A5A5A,
0xA5A5A5A5, 0xA5A5A5A5, 0x5A5A5A5A, 0x5A5A5A5A,
0x5A5A5A5A, 0x5A5A5A5A, 0xA5A5A5A5, 0xA5A5A5A5,
0x5A5A5A5A, 0x5A5A5A5A, 0xA5A5A5A5, 0xA5A5A5A5,
0xAA55AA55, 0xAA55AA55, 0x55AA55AA, 0x55AA55AA,
0xAA55AA55, 0xAA55AA55, 0x55AA55AA, 0x55AA55AA,
0x55AA55AA, 0x55AA55AA, 0xAA55AA55, 0xAA55AA55,
0x55AA55AA, 0x55AA55AA, 0xAA55AA55, 0xAA55AA55 };
ram_pointer = (volatile u32 *)start_addr;
for (wr_dqs_shift = 64; wr_dqs_shift < 96; wr_dqs_shift++) {
/*for (wr_dqs_shift=1; wr_dqs_shift<96; wr_dqs_shift++) {*/
/*
* De-assert 'start' parameter.
*/
mtdcr(ddrcfga, DDR0_02);
val = (mfdcr(ddrcfgd) & ~DDR0_02_START_MASK) | DDR0_02_START_OFF;
mtdcr(ddrcfgd, val);
/*
* Set 'wr_dqs_shift'
*/
mtdcr(ddrcfga, DDR0_09);
val = (mfdcr(ddrcfgd) & ~DDR0_09_WR_DQS_SHIFT_MASK)
| DDR0_09_WR_DQS_SHIFT_ENCODE(wr_dqs_shift);
mtdcr(ddrcfgd, val);
/*
* Set 'dqs_out_shift' = wr_dqs_shift + 32
*/
dqs_out_shift = wr_dqs_shift + 32;
mtdcr(ddrcfga, DDR0_22);
val = (mfdcr(ddrcfgd) & ~DDR0_22_DQS_OUT_SHIFT_MASK)
| DDR0_22_DQS_OUT_SHIFT_ENCODE(dqs_out_shift);
mtdcr(ddrcfgd, val);
passing_cases = 0;
for (dll_dqs_delay_X = 1; dll_dqs_delay_X < 64; dll_dqs_delay_X++) {
/*for (dll_dqs_delay_X=1; dll_dqs_delay_X<128; dll_dqs_delay_X++) {*/
/*
* Set 'dll_dqs_delay_X'.
*/
/* dll_dqs_delay_0 */
mtdcr(ddrcfga, DDR0_17);
val = (mfdcr(ddrcfgd) & ~DDR0_17_DLL_DQS_DELAY_0_MASK)
| DDR0_17_DLL_DQS_DELAY_0_ENCODE(dll_dqs_delay_X);
mtdcr(ddrcfgd, val);
/* dll_dqs_delay_1 to dll_dqs_delay_4 */
mtdcr(ddrcfga, DDR0_18);
val = (mfdcr(ddrcfgd) & ~DDR0_18_DLL_DQS_DELAY_X_MASK)
| DDR0_18_DLL_DQS_DELAY_4_ENCODE(dll_dqs_delay_X)
| DDR0_18_DLL_DQS_DELAY_3_ENCODE(dll_dqs_delay_X)
| DDR0_18_DLL_DQS_DELAY_2_ENCODE(dll_dqs_delay_X)
| DDR0_18_DLL_DQS_DELAY_1_ENCODE(dll_dqs_delay_X);
mtdcr(ddrcfgd, val);
/* dll_dqs_delay_5 to dll_dqs_delay_8 */
mtdcr(ddrcfga, DDR0_19);
val = (mfdcr(ddrcfgd) & ~DDR0_19_DLL_DQS_DELAY_X_MASK)
| DDR0_19_DLL_DQS_DELAY_8_ENCODE(dll_dqs_delay_X)
| DDR0_19_DLL_DQS_DELAY_7_ENCODE(dll_dqs_delay_X)
| DDR0_19_DLL_DQS_DELAY_6_ENCODE(dll_dqs_delay_X)
| DDR0_19_DLL_DQS_DELAY_5_ENCODE(dll_dqs_delay_X);
mtdcr(ddrcfgd, val);
ppcMsync();
ppcMbar();
/*
* Assert 'start' parameter.
*/
mtdcr(ddrcfga, DDR0_02);
val = (mfdcr(ddrcfgd) & ~DDR0_02_START_MASK) | DDR0_02_START_ON;
mtdcr(ddrcfgd, val);
ppcMsync();
ppcMbar();
/*
* Wait for the DCC master delay line to finish calibration
*/
if (wait_for_dlllock() != 0) {
printf("dlllock did not occur !!!\n");
printf("denali_core_search_data_eye!!!\n");
printf("wr_dqs_shift = %d - dll_dqs_delay_X = %d\n",
wr_dqs_shift, dll_dqs_delay_X);
hang();
}
ppcMsync();
ppcMbar();
if (wait_for_dram_init_complete() != 0) {
printf("dram init complete did not occur !!!\n");
printf("denali_core_search_data_eye!!!\n");
printf("wr_dqs_shift = %d - dll_dqs_delay_X = %d\n",
wr_dqs_shift, dll_dqs_delay_X);
hang();
}
udelay(100); /* wait 100us to ensure init is really completed !!! */
/* write values */
for (j=0; j<NUM_TRIES; j++) {
ram_pointer[j] = test[j];
/* clear any cache at ram location */
__asm__("dcbf 0,%0": :"r" (&ram_pointer[j]));
}
/* read values back */
for (j=0; j<NUM_TRIES; j++) {
for (k=0; k<NUM_READS; k++) {
/* clear any cache at ram location */
__asm__("dcbf 0,%0": :"r" (&ram_pointer[j]));
if (ram_pointer[j] != test[j])
break;
}
/* read error */
if (k != NUM_READS)
break;
}
/* See if the dll_dqs_delay_X value passed.*/
if (j < NUM_TRIES) {
/* Failed */
passing_cases = 0;
/* break; */
} else {
/* Passed */
if (passing_cases == 0)
dll_dqs_delay_X_sw_val = dll_dqs_delay_X;
passing_cases++;
if (passing_cases >= max_passing_cases) {
max_passing_cases = passing_cases;
wr_dqs_shift_with_max_passing_cases = wr_dqs_shift;
dll_dqs_delay_X_start_window = dll_dqs_delay_X_sw_val;
dll_dqs_delay_X_end_window = dll_dqs_delay_X;
}
}
/*
* De-assert 'start' parameter.
*/
mtdcr(ddrcfga, DDR0_02);
val = (mfdcr(ddrcfgd) & ~DDR0_02_START_MASK) | DDR0_02_START_OFF;
mtdcr(ddrcfgd, val);
} /* for (dll_dqs_delay_X=0; dll_dqs_delay_X<128; dll_dqs_delay_X++) */
} /* for (wr_dqs_shift=0; wr_dqs_shift<96; wr_dqs_shift++) */
/*
* Largest passing window is now detected.
*/
/* Compute dll_dqs_delay_X value */
dll_dqs_delay_X = (dll_dqs_delay_X_end_window + dll_dqs_delay_X_start_window) / 2;
wr_dqs_shift = wr_dqs_shift_with_max_passing_cases;
debug("DQS calibration - Window detected:\n");
debug("max_passing_cases = %d\n", max_passing_cases);
debug("wr_dqs_shift = %d\n", wr_dqs_shift);
debug("dll_dqs_delay_X = %d\n", dll_dqs_delay_X);
debug("dll_dqs_delay_X window = %d - %d\n",
dll_dqs_delay_X_start_window, dll_dqs_delay_X_end_window);
/*
* De-assert 'start' parameter.
*/
mtdcr(ddrcfga, DDR0_02);
val = (mfdcr(ddrcfgd) & ~DDR0_02_START_MASK) | DDR0_02_START_OFF;
mtdcr(ddrcfgd, val);
/*
* Set 'wr_dqs_shift'
*/
mtdcr(ddrcfga, DDR0_09);
val = (mfdcr(ddrcfgd) & ~DDR0_09_WR_DQS_SHIFT_MASK)
| DDR0_09_WR_DQS_SHIFT_ENCODE(wr_dqs_shift);
mtdcr(ddrcfgd, val);
debug("DDR0_09=0x%08lx\n", val);
/*
* Set 'dqs_out_shift' = wr_dqs_shift + 32
*/
dqs_out_shift = wr_dqs_shift + 32;
mtdcr(ddrcfga, DDR0_22);
val = (mfdcr(ddrcfgd) & ~DDR0_22_DQS_OUT_SHIFT_MASK)
| DDR0_22_DQS_OUT_SHIFT_ENCODE(dqs_out_shift);
mtdcr(ddrcfgd, val);
debug("DDR0_22=0x%08lx\n", val);
/*
* Set 'dll_dqs_delay_X'.
*/
/* dll_dqs_delay_0 */
mtdcr(ddrcfga, DDR0_17);
val = (mfdcr(ddrcfgd) & ~DDR0_17_DLL_DQS_DELAY_0_MASK)
| DDR0_17_DLL_DQS_DELAY_0_ENCODE(dll_dqs_delay_X);
mtdcr(ddrcfgd, val);
debug("DDR0_17=0x%08lx\n", val);
/* dll_dqs_delay_1 to dll_dqs_delay_4 */
mtdcr(ddrcfga, DDR0_18);
val = (mfdcr(ddrcfgd) & ~DDR0_18_DLL_DQS_DELAY_X_MASK)
| DDR0_18_DLL_DQS_DELAY_4_ENCODE(dll_dqs_delay_X)
| DDR0_18_DLL_DQS_DELAY_3_ENCODE(dll_dqs_delay_X)
| DDR0_18_DLL_DQS_DELAY_2_ENCODE(dll_dqs_delay_X)
| DDR0_18_DLL_DQS_DELAY_1_ENCODE(dll_dqs_delay_X);
mtdcr(ddrcfgd, val);
debug("DDR0_18=0x%08lx\n", val);
/* dll_dqs_delay_5 to dll_dqs_delay_8 */
mtdcr(ddrcfga, DDR0_19);
val = (mfdcr(ddrcfgd) & ~DDR0_19_DLL_DQS_DELAY_X_MASK)
| DDR0_19_DLL_DQS_DELAY_8_ENCODE(dll_dqs_delay_X)
| DDR0_19_DLL_DQS_DELAY_7_ENCODE(dll_dqs_delay_X)
| DDR0_19_DLL_DQS_DELAY_6_ENCODE(dll_dqs_delay_X)
| DDR0_19_DLL_DQS_DELAY_5_ENCODE(dll_dqs_delay_X);
mtdcr(ddrcfgd, val);
debug("DDR0_19=0x%08lx\n", val);
/*
* Assert 'start' parameter.
*/
mtdcr(ddrcfga, DDR0_02);
val = (mfdcr(ddrcfgd) & ~DDR0_02_START_MASK) | DDR0_02_START_ON;
mtdcr(ddrcfgd, val);
ppcMsync();
ppcMbar();
/*
* Wait for the DCC master delay line to finish calibration
*/
if (wait_for_dlllock() != 0) {
printf("dlllock did not occur !!!\n");
hang();
}
ppcMsync();
ppcMbar();
if (wait_for_dram_init_complete() != 0) {
printf("dram init complete did not occur !!!\n");
hang();
}
udelay(100); /* wait 100us to ensure init is really completed !!! */
}
#endif /* CONFIG_DDR_DATA_EYE */
#ifdef CONFIG_DDR_ECC
static void wait_ddr_idle(void)
{
/*
* Controller idle status cannot be determined for Denali
* DDR2 code. Just return here.
*/
}
static void blank_string(int size)
{
int i;
for (i=0; i<size; i++)
putc('\b');
for (i=0; i<size; i++)
putc(' ');
for (i=0; i<size; i++)
putc('\b');
}
static void program_ecc(u32 start_address,
u32 num_bytes,
u32 tlb_word2_i_value)
{
u32 current_address;
u32 end_address;
u32 address_increment;
u32 val;
char str[] = "ECC generation -";
char slash[] = "\\|/-\\|/-";
int loop = 0;
int loopi = 0;
current_address = start_address;
sync();
eieio();
wait_ddr_idle();
if (tlb_word2_i_value == TLB_WORD2_I_ENABLE) {
/* ECC bit set method for non-cached memory */
address_increment = 4;
end_address = current_address + num_bytes;
puts(str);
while (current_address < end_address) {
*((u32 *)current_address) = 0x00000000;
current_address += address_increment;
if ((loop++ % (2 << 20)) == 0) {
putc('\b');
putc(slash[loopi++ % 8]);
}
}
blank_string(strlen(str));
} else {
/* ECC bit set method for cached memory */
#if 0 /* test-only: will remove this define later, when ECC problems are solved! */
/*
* Some boards (like lwmon5) need to preserve the memory
* content upon ECC generation (for the log-buffer).
* Therefore we don't fill the memory with a pattern or
* just zero it, but write the same values back that are
* already in the memory cells.
*/
address_increment = CFG_CACHELINE_SIZE;
end_address = current_address + num_bytes;
current_address = start_address;
while (current_address < end_address) {
/*
* TODO: Th following sequence doesn't work correctly.
* Just invalidating and flushing the cache doesn't
* seem to trigger the re-write of the memory.
*/
ppcDcbi(current_address);
ppcDcbf(current_address);
current_address += CFG_CACHELINE_SIZE;
}
#else
dcbz_area(start_address, num_bytes);
dflush();
#endif
}
sync();
eieio();
wait_ddr_idle();
/* Clear error status */
mfsdram(DDR0_00, val);
mtsdram(DDR0_00, val | DDR0_00_INT_ACK_ALL);
/* Set 'int_mask' parameter to functionnal value */
mfsdram(DDR0_01, val);
mtsdram(DDR0_01, ((val &~ DDR0_01_INT_MASK_MASK) | DDR0_01_INT_MASK_ALL_OFF));
sync();
eieio();
wait_ddr_idle();
}
#endif
/*************************************************************************
*
* initdram -- 440EPx's DDR controller is a DENALI Core
*
************************************************************************/
long int initdram (int board_type)
{
#if 0 /* test-only: will remove this define later, when ECC problems are solved! */
/* CL=3 */
mtsdram(DDR0_02, 0x00000000);
mtsdram(DDR0_00, 0x0000190A);
mtsdram(DDR0_01, 0x01000000);
mtsdram(DDR0_03, 0x02030603); /* A suitable burst length was taken. CAS is right for our board */
mtsdram(DDR0_04, 0x0A030300);
mtsdram(DDR0_05, 0x02020308);
mtsdram(DDR0_06, 0x0103C812);
mtsdram(DDR0_07, 0x00090100);
mtsdram(DDR0_08, 0x02c80001);
mtsdram(DDR0_09, 0x00011D5F);
mtsdram(DDR0_10, 0x00000300);
mtsdram(DDR0_11, 0x000CC800);
mtsdram(DDR0_12, 0x00000003);
mtsdram(DDR0_14, 0x00000000);
mtsdram(DDR0_17, 0x1e000000);
mtsdram(DDR0_18, 0x1e1e1e1e);
mtsdram(DDR0_19, 0x1e1e1e1e);
mtsdram(DDR0_20, 0x0B0B0B0B);
mtsdram(DDR0_21, 0x0B0B0B0B);
#ifdef CONFIG_DDR_ECC
mtsdram(DDR0_22, 0x00267F0B | DDR0_22_CTRL_RAW_ECC_ENABLE); /* enable ECC */
#else
mtsdram(DDR0_22, 0x00267F0B);
#endif
mtsdram(DDR0_23, 0x01000000);
mtsdram(DDR0_24, 0x01010001);
mtsdram(DDR0_26, 0x2D93028A);
mtsdram(DDR0_27, 0x0784682B);
mtsdram(DDR0_28, 0x00000080);
mtsdram(DDR0_31, 0x00000000);
mtsdram(DDR0_42, 0x01000006);
mtsdram(DDR0_43, 0x030A0200);
mtsdram(DDR0_44, 0x00000003);
mtsdram(DDR0_02, 0x00000001); /* Activate the denali core */
#else
/* CL=4 */
mtsdram(DDR0_02, 0x00000000);
mtsdram(DDR0_00, 0x0000190A);
mtsdram(DDR0_01, 0x01000000);
mtsdram(DDR0_03, 0x02040803); /* A suitable burst length was taken. CAS is right for our board */
mtsdram(DDR0_04, 0x0B030300);
mtsdram(DDR0_05, 0x02020308);
mtsdram(DDR0_06, 0x0003C812);
mtsdram(DDR0_07, 0x00090100);
mtsdram(DDR0_08, 0x03c80001);
mtsdram(DDR0_09, 0x00011D5F);
mtsdram(DDR0_10, 0x00000300);
mtsdram(DDR0_11, 0x000CC800);
mtsdram(DDR0_12, 0x00000003);
mtsdram(DDR0_14, 0x00000000);
mtsdram(DDR0_17, 0x1e000000);
mtsdram(DDR0_18, 0x1e1e1e1e);
mtsdram(DDR0_19, 0x1e1e1e1e);
mtsdram(DDR0_20, 0x0B0B0B0B);
mtsdram(DDR0_21, 0x0B0B0B0B);
#ifdef CONFIG_DDR_ECC
mtsdram(DDR0_22, 0x00267F0B | DDR0_22_CTRL_RAW_ECC_ENABLE); /* enable ECC */
#else
mtsdram(DDR0_22, 0x00267F0B);
#endif
mtsdram(DDR0_23, 0x01000000);
mtsdram(DDR0_24, 0x01010001);
mtsdram(DDR0_26, 0x2D93028A);
mtsdram(DDR0_27, 0x0784682B);
mtsdram(DDR0_28, 0x00000080);
mtsdram(DDR0_31, 0x00000000);
mtsdram(DDR0_42, 0x01000008);
mtsdram(DDR0_43, 0x050A0200);
mtsdram(DDR0_44, 0x00000005);
mtsdram(DDR0_02, 0x00000001); /* Activate the denali core */
#endif
wait_for_dlllock();
/*
* Program tlb entries for this size (dynamic)
*/
program_tlb(0, 0, CFG_MBYTES_SDRAM << 20, MY_TLB_WORD2_I_ENABLE);
/*
* Setup 2nd TLB with same physical address but different virtual address
* with cache enabled. This is done for fast ECC generation.
*/
program_tlb(0, CFG_DDR_CACHED_ADDR, CFG_MBYTES_SDRAM << 20, 0);
#ifdef CONFIG_DDR_DATA_EYE
/*
* Perform data eye search if requested.
*/
denali_core_search_data_eye(CFG_DDR_CACHED_ADDR, CFG_MBYTES_SDRAM << 20);
#endif
#ifdef CONFIG_DDR_ECC
/*
* If ECC is enabled, initialize the parity bits.
*/
program_ecc(CFG_DDR_CACHED_ADDR, CFG_MBYTES_SDRAM << 20, 0);
#endif
/*
* Clear possible errors resulting from data-eye-search.
* If not done, then we could get an interrupt later on when
* exceptions are enabled.
*/
set_mcsr(get_mcsr());
return (CFG_MBYTES_SDRAM << 20);
}