使用的SDK为 ti-sdk-am335x-evm-08.00.00.00 ，想测试DDR3的稳定性，请问：
1. uboot中没有mtest命令，请问怎么添加?
2. mtest会自动避开uboot使用的内存区域吗？ 或者uboot自己使用的内存区域范围是多少？
uboot中输入"?"显示支持的命令如下，没有mtest：
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U-Boot SPL 2014.07-00110-gfb741e0-dirty (Jun 18 2019 - 14:49:28)
stone first
sdram init
reading args
spl_load_image_fat_os: error reading image args, err - -1
reading u-boot.img
reading u-boot.img
U-Boot 2014.07-00110-gfb741e0-dirty (Jun 28 2019 - 15:32:11)
I2C: ready
DRAM: 512 MiB
NAND: 0 MiB
MMC: OMAP SD/MMC: 0, OMAP SD/MMC: 1
reading uboot.env
** Unable to read "uboot.env" from mmc0:1 **
Using default environment
Net: <ethaddr> not set. Validating first E-fuse MAC
cpsw, usb_ether
Hit any key to stop autoboot: 0
U-Boot#
U-Boot# ？
Unknown command '？' - try 'help'
U-Boot# ?
? - alias for 'help'
askenv - get environment variables from stdin
base - print or set address offset
bdinfo - print Board Info structure
boot - boot default, i.e., run 'bootcmd'
bootd - boot default, i.e., run 'bootcmd'
bootm - boot application image from memory
bootp - boot image via network using BOOTP/TFTP protocol
bootz - boot Linux zImage image from memory
chpart - change active partition
cmp - memory compare
coninfo - print console devices and information
cp - memory copy
crc32 - checksum calculation
dfu - Device Firmware Upgrade
dhcp - boot image via network using DHCP/TFTP protocol
echo - echo args to console
editenv - edit environment variable
eeprom - EEPROM sub-system
env - environment handling commands
exit - exit script
ext2load- load binary file from a Ext2 filesystem
ext2ls - list files in a directory (default /)
ext4load- load binary file from a Ext4 filesystem
ext4ls - list files in a directory (default /)
false - do nothing, unsuccessfully
fatinfo - print information about filesystem
fatload - load binary file from a dos filesystem
fatls - list files in a directory (default /)
fatwrite- write file into a dos filesystem
fdt - flattened device tree utility commands
go - start application at address 'addr'
gpio - query and control gpio pins
gpt - GUID Partition Table
help - print command description/usage
i2c - I2C sub-system
iminfo - print header information for application image
imxtract- extract a part of a multi-image
itest - return true/false on integer compare
load - load binary file from a filesystem
loadb - load binary file over serial line (kermit mode)
loads - load S-Record file over serial line
loadx - load binary file over serial line (xmodem mode)
loady - load binary file over serial line (ymodem mode)
loop - infinite loop on address range
ls - list files in a directory (default /)
md - memory display
mdio - MDIO utility commands
mii - MII utility commands
mm - memory modify (auto-incrementing address)
mmc - MMC sub system
mmcinfo - display MMC info
mtdparts- define flash/nand partitions
mw - memory write (fill)
nand - NAND sub-system
nboot - boot from NAND device
nfs - boot image via network using NFS protocol
nm - memory modify (constant address)
part - disk partition related commands
ping - send ICMP ECHO_REQUEST to network host
printenv- print environment variables
reset - Perform RESET of the CPU
run - run commands in an environment variable
saveenv - save environment variables to persistent storage
setenv - set environment variables
sf - SPI flash sub-system
showvar - print local hushshell variables
sleep - delay execution for some time
source - run script from memory
spl - SPL configuration
sspi - SPI utility command
test - minimal test like /bin/sh
tftpboot- boot image via network using TFTP protocol
true - do nothing, successfully
usb - USB sub-system
usbboot - boot from USB device
version - print monitor, compiler and linker version
