WinLink E850-96 board

Overview

WinLink’s E850-96 board [1] is based on Samsung Exynos850 SoC and follows 96Boards Consumer Edition specification [2]. That makes it possible to use 96Boards mezzanine boards [3] along with it. It’s an open-hardware board and the hardware design files [4] were published, along with the supported software [5] and related documentation.

U-Boot can be used on E850-96 instead of the original Samsung LittleKernel based bootloader [6]. Because FWBL1 [7] doesn’t verify bootloader’s signature, there is no need to sign a U-Boot binary. That means U-Boot binary can be flashed into bootloader partition (instead of LittleKernel bootloader) and it will just work.

Because BL2 bootloader already sets up DRAM and runs the final bootloader (U-Boot) from DRAM, there is no need in U-Boot SPL. It’s enough to have only U-Boot proper (u-boot.bin).

Boot Flow

The boot path for Exynos850 is shown on the figure below.

Legend:

BL0: Boot ROM code
BL1: Software part of Boot ROM
EPBL: Exynos Primary Boot Loader
BL2: Initializes CMU and DRAM and runs the final bootloader
Bootloader: Final bootloader (e.g. U-Boot); also called BL33 in terms of ARM boot flow
EL3_MON: EL3 monitor (trusted firmware, handles SMC calls); also called BL31 in terms of ARM boot flow
LDFW: Loadable Firmware

Unbricking Note

In case the board is bricked for some reason, the dltool [8] can be used to unbrick and revive it. This tool performs USB boot, and uploads the LittleKernel bootloader over USB, which is then being executed on the board. The loaded bootloader further enters fastboot mode, so that the user can flash the functional bootloader binary (U-Boot or LittleKernel [7]) to eMMC using fastboot tool. Please read the dltool README file for more details about the procedure.

Build Procedure

Build U-Boot binary from source code (using AArch64 baremetal GCC toolchain):

export PATH=<toolchain path>/bin:$PATH
export CROSS_COMPILE=<toolchain prefix>
make e850-96_defconfig
make

The original E850-96 board is shipped with LittleKernel-based bootloader flashed in eMMC. To replace it with U-Boot, boot into fastboot mode (as described in the board software documentation [9]), and flash U-Boot binary:

fastboot flash bootloader u-boot.bin
fastboot reboot

U-Boot will boot up to the shell.

Flashing

User area of eMMC contains GPT partition table (either Linux or Android). Boot Partition A (mmc0boot0) contains all firmware/bootloaders. Boot Partition B (mmc0boot1) contains U-Boot environment.

First make sure to format eMMC accordingly. Prepare the initial environment:

env default -f -a
env save

For Linux, just format eMMC using default $partitions definitions:

gpt write mmc 0 $partitions

For Android, use $partitions_android instead:

setenv partitions_linux $partitions
setenv partitions $partitions_android
env save
gpt write mmc 0 $partitions

In case of Linux, there are two partitions available: esp (EFI System Partition) and rootfs. It is recommended to use fastboot to flash images to those partitions. Enter fastboot mode on your device:

fastboot usb 0

And then flash the images:

fastboot flash esp esp.img
fastboot flash rootfs rootfs.img

To update the firmware, it’s easier to use DFU. Enter DFU mode on the board:

dfu 0 mmc 0

To update U-Boot:

dfu-util -D u-boot.bin -a bootloader

It’s also possible to use fastboot to flash the whole mmc0boot0 HW partition, but it’s not so straightforward, as one have to prepare the image for the whole boot0 partition containing all firmware binaries first.