docs: add ae350-ax45mp document

Signed-off-by: Yu Chien Peter Lin <peterlin@andestech.com>

docs/AE350-AX45MP.md

@@ -0,0 +1,64 @@
+Andes AE350 AX45MP Platform
+=======
+
+AE350 is an AXI/AHB-based platform with level-one memories,
+interrupt controller, debug module, AXI and AHB Bus Matrix
+Controller, AXI-to-AHB Bridge and a collection of fundamental
+AHB/APB bus IP components pre-integrated together as a system
+design.
+
+The `ae350-ax45mp` machine configuration helps developers build
+a disk image based on mainline Linux kernel 5.18 with MMC, DMA,
+Ethernet and RTC drivers support, hosted on Andestech Github.
+
+How to build
+=============
+
+```
+$ SHELL=/bin/bash kas-container build ./meta-riscv/ae350-ax45mp.yml
+```
+
+The `kas-container` script can be obtained from
+[kas repository](https://github.com/siemens/kas/blob/3.0.2/kas-container).
+
+Build results
+=============
+
+- core-image-minimal-ae350-ax45mp.wic.gz
+- fitImage
+- ae350_ax45mp.dtb
+- boot.scr.uimg
+- uEnv.txt
+- u-boot-spl.bin
+- u-boot.itb
+
+Flashing SD card
+==============
+
+```
+gunzip -c core-image-minimal-ae350-ax45mp.wic.gz | sudo dd of=/dev/sdX bs=4M iflag=fullblock oflag=direct conv=fsync status=progress && sync
+```
+
+(Optional.) Flashing U-boot SPL
+==============
+
+If you need to update the SPL, the first partition holds XIP mode SPL
+(u-boot-spl.bin) that can be burned on flash by using the `sf` command
+shown below in U-boot prompt or [SPI_Burn tool](https://github.com/andestech/Andes-Development-Kit).
+
+```
+RISC-V # fatload mmc 0:1 0x600000 u-boot-spl.bin
+RISC-V # sf probe 0:0 50000000 0
+RISC-V # sf erase 0x0 0x10000
+RISC-V # sf write 0x600000 0x0 0x10000
+```
+
+Connect to the UART console and reset the board, it should boot
+from MMC and loads fw_dynamic.bin and u-boot.bin from u-boot.itb
+located at first partition.
+
+Resources
+==============
+
+* [Buildroot AE350 README](https://github.com/buildroot/buildroot/blob/master/board/andes/ae350/readme.txt)
+* [Andestech AndesCore™ AX45MP Multicore](http://www.andestech.com/en/products-solutions/andescore-processors/riscv-ax45mp/)