TI中文支持网CPUAM3352-1G，调试串口使用UART0。通过串口的xmodern加载u-boot-spl.bin。
UBOOT从旧版本升级到新版本，发现串口没有输出。相同的硬件旧版本SPL是有输出的，新版本SPL没有信息。逐个版本回退，发现SDK01_00_00_03还是能正常输出，升级到SDK02_00_00_00就没有串口输出。
因为硬件设计的问题，且没有仿真器，需要修改UBOOT的SPL代码进行调试，
代码交叉对比，在SDK02_00_00_00同步SDK01_00_00_03修改以下文件，SPL可以串口输出
board.c中增加红色部分的初始化代码，从SDK01_00_00_03对应同步
void s_init(void)
{
#if defined(CONFIG_SPL_BUILD) && defined(CONFIG_SPL_RTC_ONLY_SUPPORT)
rtc_only();
#endif
/*
* The ROM will only have set up sufficient pinmux to allow for the
* first 4KiB NOR to be read, we must finish doing what we know of
* the NOR mux in this space in order to continue.
*/
#ifdef CONFIG_NOR_BOOT
enable_norboot_pin_mux();
#endif
watchdog_disable();
set_uart_mux_conf();
setup_clocks_for_console();
uart_soft_reset();
#if defined(CONFIG_NOR_BOOT) || defined(CONFIG_QSPI_BOOT)
/* TODO: This does not work, gd is not available yet */
gd->baudrate = CONFIG_BAUDRATE;
serial_init();
gd->have_console = 1;
#elif defined(CONFIG_SPL_BUILD)
gd = &gdata;
preloader_console_init();
#endif
#if defined(CONFIG_SPL_AM33XX_ENABLE_RTC32K_OSC)
/* Enable RTC32K clock */
rtc32k_enable();
#endif
#ifdef CONFIG_SPL_BUILD
board_early_init_f();
#endif
}
#endif
在以下三个文件中人为修改代码中预编译的宏定义，人为屏蔽CONFIG_DM
*****************************************
lowlevel_init.S
ENTRY(lowlevel_init)
/*
* Setup a temporary stack. Global data is not available yet.
*/
ldr sp, =CONFIG_SYS_INIT_SP_ADDR
bic sp, sp, #7 /* 8-byte alignment for ABI compliance */
#ifdef CONFIG_DM1
mov r9, #0
#else
/*
* Set up global data for boards that still need it. This will be
* removed soon.
*/
#ifdef CONFIG_SPL_BUILD
ldr r9, =gdata
#else
sub sp, sp, #GD_SIZE
bic sp, sp, #7
mov r9, sp
#endif
#endif
*******************************************
spl.h
#ifndef CONFIG_DM1
extern gd_t gdata;
#endif
********************************************
spi.c
#ifndef CONFIG_DM1
/* Pointer to as well as the global data structure for SPL */
DECLARE_GLOBAL_DATA_PTR;
/*
* WARNING: This is going away very soon. Don't use it and don't submit
* pafches that rely on it. The global_data area is set up in crt0.S.
*/
gd_t gdata __attribute__ ((section(".data")));
#endif
/*
* In the context of SPL, board_init_f must ensure that any clocks/etc for
* DDR are enabled, ensure that the stack pointer is valid, clear the BSS
* and call board_init_f. We provide this version by default but mark it
* as __weak to allow for platforms to do this in their own way if needed.
*/
void __weak board_init_f(ulong dummy)
{
/* Clear the BSS. */
memset(__bss_start, 0, __bss_end – __bss_start);
#ifndef CONFIG_DM1
/* TODO: Remove settings of the global data pointer here */
gd = &gdata;
#endif
board_init_r(NULL, 0);
}
问题：
问题1：SPL中是否不支持DM？为什么SPL又生成CONFIG_DM宏
在生成的spl/u-boot-spl.cfg中有定义“#define CONFIG_DM 1”，Device Model，而其它没有定义
#define CONFIG_DM_STDIO 1
#define CONFIG_DM_GPIO 1
#define CONFIG_DM_SEQ_ALIAS 1
#define CONFIG_DM_DEVICE_REMOVE 1
#define CONFIG_DM_WARN 1
#define CONFIG_DM_SERIAL 1
问题2：串口驱动的代码没有修改，只需要CPU和板极的初始化代码调整，即可串口输出。这是代码问题？
Daniel Yoo：
换一个方式提问，SPL的串口是否能使用嘛？
