diff --git a/doc/board/AndesTech/ax25-ae350.rst b/doc/board/AndesTech/ax25-ae350.rst
index 7a01893..a7bd1a7 100644
--- a/doc/board/AndesTech/ax25-ae350.rst
+++ b/doc/board/AndesTech/ax25-ae350.rst
@@ -324,6 +324,209 @@
    / #
 
 
-TODO
-----
-Boot bbl and riscv-linux via U-Boot on AE350 board
+Running U-Boot SPL
+------------------
+The U-Boot SPL will boot in M mode and load the FIT image which include
+OpenSBI and U-Boot proper images. After loading progress, it will jump
+to OpenSBI first and then U-Boot proper which will run in S mode.
+
+
+How to build U-Boot SPL
+-----------------------
+Before building U-Boot SPL, OpenSBI must be build first. OpenSBI can be
+cloned and build for AE350 as below:
+
+git clone https://github.com/riscv/opensbi.git
+cd opensbi
+make PLATFORM=andes/ae350
+
+Copy OpenSBI FW_DYNAMIC image (build\platform\andes\ae350\firmware\fw_dynamic.bin)
+into U-Boot root directory
+
+
+How to build U-Boot SPL booting from RAM
+----------------------------------------
+With ae350_rv[32|64]_spl_defconfigs:
+
+U-Boot SPL will be loaded by gdb or FSBL and runs in RAM in machine mode
+and then load FIT image from RAM device on AE350.
+
+
+How to build U-Boot SPL booting from ROM
+----------------------------------------
+With ae350_rv[32|64]_spl_xip_defconfigs:
+
+U-Boot SPL can be burned into SPI flash and run in flash in machine mode
+and then load FIT image from SPI flash or MMC device on AE350.
+
+
+Messages of U-Boot SPL boots Kernel on AE350 board
+--------------------------------------------------
+
+.. code-block:: none
+
+U-Boot SPL 2020.01-rc1-00292-g67a3313-dirty (Nov 14 2019 - 11:26:21 +0800)
+Trying to boot from RAM
+
+OpenSBI v0.5-1-gdd8ef28 (Nov 14 2019 11:08:39)
+   ____                    _____ ____ _____
+  / __ \                  / ____|  _ \_   _|
+ | |  | |_ __   ___ _ __ | (___ | |_) || |
+ | |  | | '_ \ / _ \ '_ \ \___ \|  _ < | |
+ | |__| | |_) |  __/ | | |____) | |_) || |_
+  \____/| .__/ \___|_| |_|_____/|____/_____|
+        | |
+        |_|
+
+Platform Name          : Andes AE350
+Platform HART Features : RV64ACIMSUX
+Platform Max HARTs     : 4
+Current Hart           : 0
+Firmware Base          : 0x0
+Firmware Size          : 84 KB
+Runtime SBI Version    : 0.2
+
+PMP0: 0x0000000000000000-0x000000000001ffff (A)
+PMP1: 0x0000000000000000-0x00000001ffffffff (A,R,W,X)
+
+
+U-Boot 2020.01-rc1-00292-g67a3313-dirty (Nov 14 2019 - 11:26:21 +0800)
+
+DRAM:  1 GiB
+Flash: 64 MiB
+MMC:   mmc@f0e00000: 0
+Loading Environment from SPI Flash... SF: Detected mx25u1635e with page size 256 Bytes, erase size 4 KiB, total 2 MiB
+OK
+In:    serial@f0300000
+Out:   serial@f0300000
+Err:   serial@f0300000
+Net:   no alias for ethernet0
+
+Warning: mac@e0100000 (eth0) using random MAC address - a2:ae:93:7b:cc:8f
+eth0: mac@e0100000
+Hit any key to stop autoboot:  0
+6455 bytes read in 31 ms (203.1 KiB/s)
+20421684 bytes read in 8647 ms (2.3 MiB/s)
+## Booting kernel from Legacy Image at 00600000 ...
+   Image Name:
+   Image Type:   RISC-V Linux Kernel Image (uncompressed)
+   Data Size:    20421620 Bytes = 19.5 MiB
+   Load Address: 00200000
+   Entry Point:  00200000
+   Verifying Checksum ... OK
+## Flattened Device Tree blob at 20000000
+   Booting using the fdt blob at 0x20000000
+   Loading Kernel Image
+   Loading Device Tree to 000000001effb000, end 000000001efff936 ... OK
+
+Starting kernel ...
+
+OF: fdt: Ignoring memory range 0x0 - 0x200000
+Linux version 4.17.0-00253-g49136e10bcb2 (sqa@atcsqa07) (gcc version 7.3.0 (2019-04-06_nds64le-linux-glibc-v5_experimental)) #1 SMP PREEMPT Sat Apr 6 23:41:49 CST 2019
+bootconsole [early0] enabled
+Initial ramdisk at: 0x        (ptrval) (13665712 bytes)
+Zone ranges:
+  DMA32    [mem 0x0000000000200000-0x000000003fffffff]
+  Normal   empty
+Movable zone start for each node
+Early memory node ranges
+  node   0: [mem 0x0000000000200000-0x000000003fffffff]
+Initmem setup node 0 [mem 0x0000000000200000-0x000000003fffffff]
+software IO TLB [mem 0x3b1f8000-0x3f1f8000] (64MB) mapped at [        (ptrval)-        (ptrval)]
+elf_platform is rv64i2p0m2p0a2p0c2p0xv5-0p0
+compatible privileged spec version 1.10
+percpu: Embedded 16 pages/cpu @        (ptrval) s28184 r8192 d29160 u65536
+Built 1 zonelists, mobility grouping on.  Total pages: 258055
+Kernel command line: console=ttyS0,38400n8 debug loglevel=7
+log_buf_len individual max cpu contribution: 4096 bytes
+log_buf_len total cpu_extra contributions: 12288 bytes
+log_buf_len min size: 16384 bytes
+log_buf_len: 32768 bytes
+early log buf free: 14608(89%)
+Dentry cache hash table entries: 131072 (order: 8, 1048576 bytes)
+Inode-cache hash table entries: 65536 (order: 7, 524288 bytes)
+Sorting __ex_table...
+Memory: 944428K/1046528K available (3979K kernel code, 246K rwdata, 1490K rodata, 13523K init, 688K bss, 102100K reserved, 0K cma-reserved)
+SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=4, Nodes=1
+Preemptible hierarchical RCU implementation.
+        Tasks RCU enabled.
+NR_IRQS: 72, nr_irqs: 72, preallocated irqs: 0
+riscv,cpu_intc,0: 64 local interrupts mapped
+riscv,cpu_intc,1: 64 local interrupts mapped
+riscv,cpu_intc,2: 64 local interrupts mapped
+riscv,cpu_intc,3: 64 local interrupts mapped
+riscv,plic0,e4000000: mapped 71 interrupts to 8/8 handlers
+clocksource: riscv_clocksource: mask: 0xffffffffffffffff max_cycles: 0x1bacf917bf, max_idle_ns: 881590412290 ns
+sched_clock: 64 bits at 60MHz, resolution 16ns, wraps every 4398046511098ns
+Console: colour dummy device 40x30
+Calibrating delay loop (skipped), value calculated using timer frequency.. 120.00 BogoMIPS (lpj=600000)
+pid_max: default: 32768 minimum: 301
+Mount-cache hash table entries: 2048 (order: 2, 16384 bytes)
+Mountpoint-cache hash table entries: 2048 (order: 2, 16384 bytes)
+Hierarchical SRCU implementation.
+smp: Bringing up secondary CPUs ...
+CPU0: online
+CPU2: online
+CPU3: online
+smp: Brought up 1 node, 4 CPUs
+devtmpfs: initialized
+random: get_random_u32 called from bucket_table_alloc+0x198/0x1d8 with crng_init=0
+clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 19112604462750000 ns
+futex hash table entries: 1024 (order: 4, 65536 bytes)
+NET: Registered protocol family 16
+Advanced Linux Sound Architecture Driver Initialized.
+clocksource: Switched to clocksource riscv_clocksource
+NET: Registered protocol family 2
+tcp_listen_portaddr_hash hash table entries: 512 (order: 1, 8192 bytes)
+TCP established hash table entries: 8192 (order: 4, 65536 bytes)
+TCP bind hash table entries: 8192 (order: 5, 131072 bytes)
+TCP: Hash tables configured (established 8192 bind 8192)
+UDP hash table entries: 512 (order: 2, 16384 bytes)
+UDP-Lite hash table entries: 512 (order: 2, 16384 bytes)
+NET: Registered protocol family 1
+RPC: Registered named UNIX socket transport module.
+RPC: Registered udp transport module.
+RPC: Registered tcp transport module.
+RPC: Registered tcp NFSv4.1 backchannel transport module.
+Unpacking initramfs...
+workingset: timestamp_bits=62 max_order=18 bucket_order=0
+NFS: Registering the id_resolver key type
+Key type id_resolver registered
+Key type id_legacy registered
+nfs4filelayout_init: NFSv4 File Layout Driver Registering...
+io scheduler noop registered
+io scheduler cfq registered (default)
+io scheduler mq-deadline registered
+io scheduler kyber registered
+Console: switching to colour frame buffer device 40x30
+Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
+console [ttyS0] disabled
+f0300000.serial: ttyS0 at MMIO 0xf0300020 (irq = 20, base_baud = 1228800) is a 16550A
+console [ttyS0] enabled
+console [ttyS0] enabled
+bootconsole [early0] disabled
+bootconsole [early0] disabled
+loop: module loaded
+tun: Universal TUN/TAP device driver, 1.6
+ftmac100: Loading version 0.2 ...
+ftmac100 e0100000.mac eth0: irq 21, mapped at         (ptrval)
+ftmac100 e0100000.mac eth0: generated random MAC address 4e:fd:bd:f3:04:fc
+ftsdc010 f0e00000.mmc: mmc0 - using hw SDIO IRQ
+mmc0: new SDHC card at address d555
+ftssp010 card registered!
+mmcblk0: mmc0:d555 SD04G 3.79 GiB
+NET: Registered protocol family 10
+ mmcblk0: p1
+Segment Routing with IPv6
+sit: IPv6, IPv4 and MPLS over IPv4 tunneling driver
+NET: Registered protocol family 17
+NET: Registered protocol family 15
+ALSA device list:
+  #0: ftssp_ac97 controller
+Freeing unused kernel memory: 13520K
+This architecture does not have kernel memory protection.
+Sysinit starting
+Sat Apr  6 23:33:53 CST 2019
+nfs4flexfilelayout_init: NFSv4 Flexfile Layout Driver Registering...
+
+~ #