分类： 嵌入式
2015-09-01 10:45:00
原文地址：*** am335x开发板的疑问以及解答 作者：andyhzw
参考文件：
1，AM335x ARM Cortex-A8 Microprocessors (MPUs) Technical Reference Manual.pdf；
2，am3359.pdf；
1，am335x的cpu上电后，会跳到哪个地址去执行？
答：
芯片到uboot启动流程 ：ROM → MLO(SPL)→ uboot.img
AM335x 中bootloader被分成了 3 个部分：
第一级 bootloader：引导加载程序，板子上电后会自动执行这些代码，如选择哪种方式启动（NAND，SDcard，UART。。。），然后跳转转到第二级 bootloader。这些代码应该是存放在 176KB 的 ROM 中。
第二级 bootloader：MLO（SPL），用以硬件初始化：关闭看门狗，关闭中断，设置 CPU 时钟频率、速度等操作。然后会跳转到第三级bootloader。MLO文件应该会被映射到 64 KB的 Internal SRAM 中。
第三级 bootloader：uboot.img，C代码的入口。
其中第一级 bootloader 是板子固化的，第二级和第三级是通过编译 uboot 所得的。
2，第二级 bootloader：MLO（SPL）做了哪些事情？
MLO(SPL)内存分布如下：
SPL内存重映射：
< PATH : /arch/arm/cpu/armv7/omap-common/u-boot-spl.lds >
MEMORY { .sram : ORIGIN = CONFIG_SPL_TEXT_BASE,\
LENGTH = CONFIG_SPL_MAX_SIZE }
MEMORY { .sdram : ORIGIN = CONFIG_SPL_BSS_START_ADDR, \
LENGTH = CONFIG_SPL_BSS_MAX_SIZE }
OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
OUTPUT_ARCH(arm)
ENTRY(_start)
SECTIONS
{
.text :
{
__start = .;
arch/arm/cpu/armv7/start.o (.text)
*(.text*)
} >.sram
. = ALIGN(4);
.rodata : { *(SORT_BY_ALIGNMENT(.rodata*)) } >.sram
. = ALIGN(4);
.data : { *(SORT_BY_ALIGNMENT(.data*)) } >.sram
. = ALIGN(4);
__image_copy_end = .;
_end = .;
.bss :
{
. = ALIGN(4);
__bss_start = .;
*(.bss*)
. = ALIGN(4);
__bss_end__ = .;
} >.sdram
}
#define CONFIG_SPL_TEXT_BASE 0x402F0400 #define CONFIG_SPL_MAX_SIZE (46 * 1024) #define CONFIG_SPL_STACK LOW_LEVEL_SRAM_STACK #define CONFIG_SPL_BSS_START_ADDR 0x80000000 #define CONFIG_SPL_BSS_MAX_SIZE 0x80000 /* 512 KB */
@1@ 保存启动参数 bl save_boot_params
/* * the actual reset code */ reset: bl save_boot_params
.global save_boot_params save_boot_params: /* * See if the rom code passed pointer is valid: * It is not valid if it is not in non-secure SRAM * This may happen if you are booting with the help of * debugger */ ldr r2, =NON_SECURE_SRAM_START cmp r2, r0 bgt 1f ldr r2, =NON_SECURE_SRAM_END cmp r2, r0 blt 1f /* * store the boot params passed from rom code or saved * and passed by SPL */ cmp r0, #0 beq 1f ldr r1, =boot_params str r0, [r1]
/*《PATH: /arch/arm/include/asm/arch-ti81xx/omap.h》 * Non-secure SRAM Addresses * Non-secure RAM starts at 0x40300000 for GP devices. But we keep SRAM_BASE * at 0x40304000(EMU base) so that our code works for both EMU and GP */ #define NON_SECURE_SRAM_START 0x40304000 #define NON_SECURE_SRAM_END 0x4030E000 #define LOW_LEVEL_SRAM_STACK 0x4030B7FC
问题：这些参数是保存在哪里的？大概有哪些参数？
答：
这些参数保存的内存地址为 64 KB 的 OCM RAM 中：
注：Dowloaded Image 区域：是用来保存 MLO（SPL） 文件的，其最大可达到 109 KB
@a2@ 设置 CPU 为 SVC32 模式
/* * set the cpu to SVC32 mode */ mrs r0, cpsr bic r0, r0, #0x1f orr r0, r0, #0xd3 msr cpsr,r0
CPSR:程序状态寄存器(current program status register)
(当前程序状态寄存器)，在任何处理器模式下被访问。它包含了条件标志位、中断禁止位、当前处理器模式标志以及其他的一些控制和状态位。
CPSR在用户级编程时用于存储条件码。
SPSR:程序状态保存寄存器（saved program status register）,每一种处理器模式下都有一个状态寄存器SPSR,SPSR用于保存CPSR的状态，以便异常返回后恢复异常发生时的工作状态。当特定 的异常中断发生时，这个寄存器用于存放当前程序状态寄存器的内容。在异常中断退出时，可以用SPSR来恢复CPSR。由于用户模式和系统模式不是异常中断 模式，所以他没有SPSR。当用户在用户模式或系统模式访问SPSR，将产生不可预知的后果。
CPSR格式如下所示。SPSR和CPSR格式相同。
31 30 29 28 27 26 7 6 5 4 3 2 1 0
N Z C V Q DNM(RAZ) I F T M4 M3 M2 M1 M0
详解：http://blog.chinaunix.net/uid-28458801-id-3487199.html
@a3@ CPU的初始化
《PATH : /arch/arm/cpu/armv7/start.S》 /* the mask ROM code should have PLL and others stable */ #ifndef CONFIG_SKIP_LOWLEVEL_INIT bl cpu_init_crit #endif
.globl lowlevel_init lowlevel_init: /* * Setup a temporary stack */ ldr sp, =LOW_LEVEL_SRAM_STACK /* * Save the old lr(passed in ip) and the current lr to stack */ push {ip, lr} /* * go setup pll, mux, memory */ bl s_init pop {ip, pc}
问题：CPU的初始化有哪些内容？
答：
@b1@ 首先要设置堆栈区，因为将会调用 C函数来实现CPU的初始化
问题：这个堆栈在什么位置，其内存大小是多少？
答
《PATH ：/arch/arm/include/asm/arch-ti81xx/omap.h》 #define LOW_LEVEL_SRAM_STACK 0x4030B7FC
@b2@ 执行 s_init() 函数，实现 CPU 的初始化
/* * early system init of muxing and clocks. */ void s_init(void) { /* Can be removed as A8 comes up with L2 enabled */ l2_cache_enable(); /* WDT1 is already running when the bootloader gets control * Disable it to avoid "random" resets */ __raw_writel(0xAAAA, WDT_WSPR); while(__raw_readl(WDT_WWPS) != 0x0); __raw_writel(0x5555, WDT_WSPR); while(__raw_readl(WDT_WWPS) != 0x0); #ifdef CONFIG_SPL_BUILD /* Setup the PLLs and the clocks for the peripherals */ pll_init(); /* Enable RTC32K clock */ rtc32k_enable(); /* UART softreset */ u32 regVal; u32 uart_base = DEFAULT_UART_BASE; enable_uart0_pin_mux(); /* IA Motor Control Board has default console on UART3*/ /* XXX: This is before we've probed / set board_id */ if (board_id == IA_BOARD) { uart_base = UART3_BASE; } regVal = __raw_readl(uart_base + UART_SYSCFG_OFFSET); regVal |= UART_RESET; __raw_writel(regVal, (uart_base + UART_SYSCFG_OFFSET) ); while ((__raw_readl(uart_base + UART_SYSSTS_OFFSET) & UART_CLK_RUNNING_MASK) != UART_CLK_RUNNING_MASK); /* Disable smart idle */ regVal = __raw_readl((uart_base + UART_SYSCFG_OFFSET)); regVal |= UART_SMART_IDLE_EN; __raw_writel(regVal, (uart_base + UART_SYSCFG_OFFSET)); /* Initialize the Timer */ init_timer(); preloader_console_init(); printf("\nlocation /board/ti/am335x\n"); //@@ /*@@*/ // led(); /*@@*/ config_am335x_ddr(); #endif }
@c1@ 使能第二级缓冲区
/* Can be removed as A8 comes up with L2 enabled */ l2_cache_enable();l2_cache_enable: push {r0, r1, r2, lr} mrc 15, 0, r3, cr1, cr0, 1 orr r3, r3, #2 mcr 15, 0, r3, cr1, cr0, 1 pop {r1, r2, r3, pc}
@c2@ 关闭看门狗（WDT）
/* WDT1 is already running when the bootloader gets control * Disable it to avoid "random" resets */ __raw_writel(0xAAAA, WDT_WSPR); while(__raw_readl(WDT_WWPS) != 0x0); __raw_writel(0x5555, WDT_WSPR); while(__raw_readl(WDT_WWPS) != 0x0);
#define WDT_WSPR (WDT_BASE + 0x048) /* Watchdog Timer */ #ifdef CONFIG_AM335X #define WDT_BASE 0x44E35000 #else #define WDT_BASE 0x480C2000 #endif
@c3@ 给外设设置好 PLL 和 时钟频率等
/* Setup the PLLs and the clocks for the peripherals */ pll_init();/* * Configure the PLL/PRCM for necessary peripherals */ void pll_init() { mpu_pll_config(MPUPLL_M_500); core_pll_config(); per_pll_config(); ddr_pll_config(); /* Enable the required interconnect clocks */ interface_clocks_enable(); /* Enable power domain transition */ power_domain_transition_enable(); /* Enable the required peripherals */ per_clocks_enable(); }
@c4@ 使能 32-KHz 频率的实时时钟
/* Enable RTC32K clock */
rtc32k_enable();
《PATH : /board/ti/am335x/evm.c》
static void rtc32k_enable(void)
{
/* Unlock the rtc's registers */
__raw_writel(0x83e70b13, (AM335X_RTC_BASE + RTC_KICK0_REG));
__raw_writel(0x95a4f1e0, (AM335X_RTC_BASE + RTC_KICK1_REG));
/* Enable the RTC 32K OSC */
__raw_writel(0x48, (AM335X_RTC_BASE + RTC_OSC_REG));
}
/* RTC base address */
#define AM335X_RTC_BASE 0x44E3E000
#define RTC_KICK0_REG 0x6c
#define RTC_KICK1_REG 0x70
#define RTC_OSC_REG 0x54
@c5@ 使能UART0
/* UART softreset */
u32 regVal;
u32 uart_base = DEFAULT_UART_BASE;
enable_uart0_pin_mux();
/* IA Motor Control Board has default console on UART3*/
/* XXX: This is before we've probed / set board_id */
if (board_id == IA_BOARD) {
uart_base = UART3_BASE;
}
regVal = __raw_readl(uart_base + UART_SYSCFG_OFFSET);
regVal |= UART_RESET;
__raw_writel(regVal, (uart_base + UART_SYSCFG_OFFSET) );
while ((__raw_readl(uart_base + UART_SYSSTS_OFFSET) &
UART_CLK_RUNNING_MASK) != UART_CLK_RUNNING_MASK);
/* Disable smart idle */
regVal = __raw_readl((uart_base + UART_SYSCFG_OFFSET));
regVal |= UART_SMART_IDLE_EN;
__raw_writel(regVal, (uart_base + UART_SYSCFG_OFFSET));
#ifdef CONFIG_AM335X
#define DEFAULT_UART_BASE UART0_BASE
#endif
#ifdef CONFIG_AM335X
#define UART0_BASE 0x44E09000
#else
#define UART0_BASE 0x48020000
#endif
@c6@ 初始化 定时器
/* Initialize the Timer */ init_timer();static void init_timer(void) { /* Reset the Timer */ __raw_writel(0x2, (DM_TIMER2_BASE + TSICR_REG)); /* Wait until the reset is done */ while (__raw_readl(DM_TIMER2_BASE + TIOCP_CFG_REG) & 1); /* Start the Timer */ __raw_writel(0x1, (DM_TIMER2_BASE + TCLR_REG)); } /* DM Timer base addresses */ #define DM_TIMER0_BASE 0x4802C000 #define DM_TIMER1_BASE 0x4802E000 #define DM_TIMER2_BASE 0x48040000 #define DM_TIMER3_BASE 0x48042000 #define DM_TIMER4_BASE 0x48044000 #define DM_TIMER5_BASE 0x48046000 #define DM_TIMER6_BASE 0x48048000 #define DM_TIMER7_BASE 0x4804A000
@c7@ 初始化控制台，通过UART可以查看相关信息
preloader_console_init();
《PATH : /arch/arm/cpu/armv7/omap-common/spl.c》
/* This requires UART clocks to be enabled */
void preloader_console_init(void)
{
const char *u_boot_rev = U_BOOT_VERSION;
char rev_string_buffer[50];
gd = &gdata;
gd->bd = &bdata;
gd->flags |= GD_FLG_RELOC;
gd->baudrate = CONFIG_BAUDRATE;
serial_init(); /* serial communications setup */
/* Avoid a second "U-Boot" coming from this string */
u_boot_rev = &u_boot_rev[7];
printf("\nU-Boot SPL %s (%s - %s)\n", u_boot_rev, U_BOOT_DATE,
U_BOOT_TIME);
omap_rev_string(rev_string_buffer);
printf("Texas Instruments %s\n", rev_string_buffer);
}
@c8@ 配置 DDR
config_am335x_ddr();
《PATH ：》
/* void DDR2_EMIF_Config(void); */
static void config_am335x_ddr(void)
{
int data_macro_0 = 0;
int data_macro_1 = 1;
enable_ddr_clocks();
config_vtp();
Cmd_Macro_Config();
Data_Macro_Config(data_macro_0);
Data_Macro_Config(data_macro_1);
__raw_writel(PHY_RANK0_DELAY, DATA0_RANK0_DELAYS_0);
__raw_writel(PHY_RANK0_DELAY, DATA1_RANK0_DELAYS_0);
__raw_writel(DDR_IOCTRL_VALUE, DDR_CMD0_IOCTRL);
__raw_writel(DDR_IOCTRL_VALUE, DDR_CMD1_IOCTRL);
__raw_writel(DDR_IOCTRL_VALUE, DDR_CMD2_IOCTRL);
__raw_writel(DDR_IOCTRL_VALUE, DDR_DATA0_IOCTRL);
__raw_writel(DDR_IOCTRL_VALUE, DDR_DATA1_IOCTRL);
__raw_writel(__raw_readl(DDR_IO_CTRL) & 0xefffffff, DDR_IO_CTRL);
__raw_writel(__raw_readl(DDR_CKE_CTRL) | 0x00000001, DDR_CKE_CTRL);
config_emif_ddr2();
}
《PATH : /arm/include/asm/arch-ti81xx/cpu.h》
#define DATA0_RANK0_DELAYS_0 (DDR_PHY_BASE_ADDR + 0x134)
#define DATA1_RANK0_DELAYS_0 (DDR_PHY_BASE_ADDR + 0x1D8)
/* DDR offsets */
#define DDR_PHY_BASE_ADDR 0x44E12000
#define DDR_IO_CTRL 0x44E10E04
#define DDR_CKE_CTRL 0x44E1131C
#define CONTROL_BASE_ADDR 0x44E10000
@c DONE@
@b DONE@
@a4@ 设置 internal RAM 内存空间的栈指针，调用 board_init_f()函数
/* Set stackpointer in internal RAM to call board_init_f */ call_board_init_f: ldr sp, =(CONFIG_SYS_INIT_SP_ADDR) bic sp, sp, #7 /* 8-byte alignment for ABI compliance */ ldr r0,=0x00000000 bl board_init_f
