DDR配置过程比较复杂，基本上是按照DDR控制器的时序要求来做的，其中很多参数要结合DDR芯片本身的参数来定，还有些参数是时序参数，要去详细计算。所以DDR配置非常繁琐、细致、专业。所以我们对DDR初始化的态度就是：学会这种思路和方法，结合文档和代码能看懂，会算一些常见的参数即可。
.global sdram_asm_init sdram_asm_init:
ldr r0, =0xf1e00000
ldr r1, =0x0
str r1, [r0, #0x0] /* DMC0 Drive Strength (Setting 2X) */ ldr r0, =ELFIN_GPIO_BASE ldr r1, =0x0000AAAA
str r1, [r0, #MP1_0DRV_SR_OFFSET] // 寄存器中对应0b10，就是2X ldr r1, =0x0000AAAA
str r1, [r0, #MP1_1DRV_SR_OFFSET] ldr r1, =0x0000AAAA
str r1, [r0, #MP1_2DRV_SR_OFFSET] ldr r1, =0x0000AAAA
str r1, [r0, #MP1_3DRV_SR_OFFSET] ldr r1, =0x0000AAAA
str r1, [r0, #MP1_4DRV_SR_OFFSET] ldr r1, =0x0000AAAA
str r1, [r0, #MP1_5DRV_SR_OFFSET] ldr r1, =0x0000AAAA
str r1, [r0, #MP1_6DRV_SR_OFFSET] ldr r1, =0x0000AAAA
str r1, [r0, #MP1_7DRV_SR_OFFSET] ldr r1, =0x00002AAA
str r1, [r0, #MP1_8DRV_SR_OFFSET] /* DMC1 Drive Strength (Setting 2X) */ ldr r0, =ELFIN_GPIO_BASE ldr r1, =0x0000AAAA
str r1, [r0, #MP2_0DRV_SR_OFFSET] ldr r1, =0x0000AAAA
str r1, [r0, #MP2_1DRV_SR_OFFSET] ldr r1, =0x0000AAAA
str r1, [r0, #MP2_2DRV_SR_OFFSET] ldr r1, =0x0000AAAA
str r1, [r0, #MP2_3DRV_SR_OFFSET] ldr r1, =0x0000AAAA
str r1, [r0, #MP2_4DRV_SR_OFFSET] ldr r1, =0x0000AAAA
str r1, [r0, #MP2_5DRV_SR_OFFSET] ldr r1, =0x0000AAAA
str r1, [r0, #MP2_6DRV_SR_OFFSET] ldr r1, =0x0000AAAA
str r1, [r0, #MP2_7DRV_SR_OFFSET] ldr r1, =0x00002AAA
str r1, [r0, #MP2_8DRV_SR_OFFSET] /* DMC0 initialization at single Type*/
ldr r0, =APB_DMC_0_BASE ldr r1, =0x00101000 @PhyControl0 DLL parameter setting, manual 0x00101000
str r1, [r0, #DMC_PHYCONTROL0] ldr r1, =0x00000086 @PhyControl1 DLL parameter setting, LPDDR/LPDDR2 Case
str r1, [r0, #DMC_PHYCONTROL1] ldr r1, =0x00101002 @PhyControl0 DLL on
str r1, [r0, #DMC_PHYCONTROL0] ldr r1, =0x00101003 @PhyControl0 DLL start
str r1, [r0, #DMC_PHYCONTROL0] find_lock_val:
ldr r1, [r0, #DMC_PHYSTATUS] @Load Phystatus register value
and r2, r1, #0x7
cmp r2, #0x7 @Loop until DLL is locked
bne find_lock_val and r1, #0x3fc0
mov r2, r1, LSL #
orr r2, r2, #0x100000
orr r2 ,r2, #0x1000 orr r1, r2, #0x3 @Force Value locking
str r1, [r0, #DMC_PHYCONTROL0] #if /* Memory margin test .. */
orr r1, r2, #0x1 @DLL off
str r1, [r0, #DMC_PHYCONTROL0]
#endif
/* setting DDR2 */
ldr r1, =0x0FFF2010 @ConControl auto refresh off
str r1, [r0, #DMC_CONCONTROL] ldr r1, =DMC0_MEMCONTROL @MemControl BL=, chip, DDR2 type, dynamic self refresh, force precharge, dynamic power down off
str r1, [r0, #DMC_MEMCONTROL] ldr r1, =DMC0_MEMCONFIG_0 @MemConfig0 256MB config, banks,Mapping Method[:]:linear, :linterleaved, :Mixed
str r1, [r0, #DMC_MEMCONFIG0] ldr r1, =DMC0_MEMCONFIG_1 @MemConfig1
str r1, [r0, #DMC_MEMCONFIG1] ldr r1, =0xFF000000 @PrechConfig
str r1, [r0, #DMC_PRECHCONFIG] ldr r1, =DMC0_TIMINGA_REF @TimingAref .8us*133MHz=(0x40E), 100MHz=(0x30C), 20MHz=(0x9C), 10MHz=(0x4E)
str r1, [r0, #DMC_TIMINGAREF] ldr r1, =DMC0_TIMING_ROW @TimingRow for @200MHz
str r1, [r0, #DMC_TIMINGROW] ldr r1, =DMC0_TIMING_DATA @TimingData CL=
str r1, [r0, #DMC_TIMINGDATA] ldr r1, =DMC0_TIMING_PWR @TimingPower
str r1, [r0, #DMC_TIMINGPOWER] ldr r1, =0x07000000 @DirectCmd chip0 Deselect
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x01000000 @DirectCmd chip0 PALL
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x00020000 @DirectCmd chip0 EMRS2
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x00030000 @DirectCmd chip0 EMRS3
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x00010400 @DirectCmd chip0 EMRS1 (MEM DLL on, DQS# disable)
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x00000542 @DirectCmd chip0 MRS (MEM DLL reset) CL=, BL=
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x01000000 @DirectCmd chip0 PALL
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x05000000 @DirectCmd chip0 REFA
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x05000000 @DirectCmd chip0 REFA
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x00000442 @DirectCmd chip0 MRS (MEM DLL unreset)
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x00010780 @DirectCmd chip0 EMRS1 (OCD default)
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x00010400 @DirectCmd chip0 EMRS1 (OCD exit)
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x07100000 @DirectCmd chip1 Deselect
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x01100000 @DirectCmd chip1 PALL
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x00120000 @DirectCmd chip1 EMRS2
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x00130000 @DirectCmd chip1 EMRS3
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x00110400 @DirectCmd chip1 EMRS1 (MEM DLL on, DQS# disable)
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x00100542 @DirectCmd chip1 MRS (MEM DLL reset) CL=, BL=
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x01100000 @DirectCmd chip1 PALL
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x05100000 @DirectCmd chip1 REFA
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x05100000 @DirectCmd chip1 REFA
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x00100442 @DirectCmd chip1 MRS (MEM DLL unreset)
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x00110780 @DirectCmd chip1 EMRS1 (OCD default)
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x00110400 @DirectCmd chip1 EMRS1 (OCD exit)
str r1, [r0, #DMC_DIRECTCMD] ldr r1, =0x0FF02030 @ConControl auto refresh on
str r1, [r0, #DMC_CONCONTROL] ldr r1, =0xFFFF00FF @PwrdnConfig
str r1, [r0, #DMC_PWRDNCONFIG] ldr r1, =0x00202400 @MemControl BL=, chip, DDR2 type, dynamic self refresh, force precharge, dynamic power down off
str r1, [r0, #DMC_MEMCONTROL] // 上面是DRAM0初始化步骤