FES

FES is a low-level USB interface used by LiveSuit to flash firmware to the device. It works on top of FEL. Thus you must activate FEL mode first, then you can enter FES mode using FEL commands.

Implementations
The FEL protocol is consistent in implementation, however the same cannot be said about FES protocol. There are two versions of the protocol, the newer one has more commands available and it's easier to switch device into FES. Allwinner uses "boot1.0" and "boot2.0" in their SDK to specify FES protocol version. The 2.0 version for the first time appeared in late 2013 along with Android 4.4 SDK release, and it's used on most devices sold with Android 4.4+.

Booting to FES
You can use  tool from Sunxi-tools to boot to FES, or FELix which has a dedicated command for that.

Boot 2.0

 * 1) You need two files from LiveSuit image: fes1.fex and u-boot.fex
 * 2) Write fes1.fex at 0x2000
 * 3) Execute code at 0x2000. If everything goes well you can access device's DRAM
 * 4) Write u-boot.fex at 0x4a000000 (sunxi's u-boot doesn't have implemented FES protocol)
 * 5) Set work mode of u-boot to USB mode: Write 0x10 at 0x4a0000e0
 * 6) Execute code at 0x4a000000

Boot 1.0
More universal, as DRAM config isn't precompiled into binaries. But it's more difficult to enter manually, because you have to recreate DRAM config. Structure of DRAM config (sun4i): uint32le :unk1, :initial_value => 0x2000000              # 0x00 uint32le :unk2, :initial_value => 0x2000000              # 0x04 uint32le :unk3, :initial_value => 0x2000100              # 0x08 uint32le :unk4, :initial_value => 128                    # 0x0C uint32le :unk5                                           # 0x10 uint32le :unk6                                           # 0x14 uint32le :uart_debug_tx, :initial_value => 0x7C4AC1      # 0x18 uint32le :uart_debug_port, :inital_value => 0            # 0x1C array   :unk7, :type => :uint32le, :initial_length => 15 # 0x20 uint32le :dram_baseaddr, :initial_value => 0x40000000    # 0x5C uint32le :dram_clk, :initial_value => 408                # 0x60 uint32le :dram_type, :initial_value => 3                 # 0x64 uint32le :dram_rank_num, :initial_value => 1             # 0x68 uint32le :dram_chip_density, :initial_value => 4096      # 0x6C uint32le :dram_io_width, :initial_value => 16            # 0x70 uint32le :dram_bus_width, :initial_value => 32           # 0x74 uint32le :dram_cas, :initial_value => 6                  # 0x78 uint32le :dram_zq, :initial_value => 0x7F                # 0x7C uint32le :dram_odt_en                                    # 0x80 uint32le :dram_size, :initial_value => 1024              # 0x84 uint32le :dram_tpr0, :initial_value => 0x30926692        # 0x88 uint32le :dram_tpr1, :initial_value => 0x1090            # 0x8C uint32le :dram_tpr2, :initial_value => 0x1A0C8           # 0x90 uint32le :dram_tpr3                                      # 0x94 uint32le :dram_tpr4                                      # 0x98 uint32le :dram_tpr5                                      # 0x9C uint32le :dram_emr1, :initial_value => 4                 # 0xA0 uint32le :dram_emr2                                      # 0xA4 uint32le :dram_emr3                                      # 0xA8 array   :unk8, :type => :uint32le, :initial_length => 2  # 0xAC Structure of DRAM config (sun6i) array   :unknown, :type => :uint8, :initial_length => 24     # 0x00 uint32le :uart_debug_tx, :initial_value => 0x7C4A87          # 0x18 uint32le :uart_debug_port, :inital_value => 0                # 0x1C uint32le :dram_clk, :initial_value => 240                    # 0x20 uint32le :dram_type, :initial_value => 3                     # 0x24 uint32le :dram_zq, :initial_value => 0xBB                    # 0x28 uint32le :dram_odt_en, :initial_value => 0                   # 0x2C uint32le :dram_para1, :initial_value => 0x10F40400           # 0x30, &=0xffff => DRAM size (1024) uint32le :dram_para2, :initial_value => 0x1211               # 0x34 uint32le :dram_mr0, :initial_value => 0x1A50                 # 0x38 uint32le :dram_mr1, :initial_value => 0                      # 0x3C uint32le :dram_mr2, :initial_value => 24                     # 0x40 uint32le :dram_mr3, :initial_value => 0                      # 0x44 uint32le :dram_tpr0, :initial_value => 0                     # 0x48 uint32le :dram_tpr1, :initial_value => 0x80000800            # 0x4C uint32le :dram_tpr2, :initial_value => 0x46270140            # 0x50 uint32le :dram_tpr3, :initial_value => 0xA0C4284C            # 0x54 uint32le :dram_tpr4, :initial_value => 0x39C8C209            # 0x58 uint32le :dram_tpr5, :initial_value => 0x694552AD            # 0x5C uint32le :dram_tpr6, :initial_value => 0x3002C4A0            # 0x60 uint32le :dram_tpr7, :initial_value => 0x2AAF9B              # 0x64 uint32le :dram_tpr8, :initial_value => 0x604111D             # 0x68 uint32le :dram_tpr9, :initial_value => 0x42DA072             # 0x6C uint32le :dram_tpr10, :initial_value => 0                    # 0x70 uint32le :dram_tpr11, :initial_value => 0                    # 0x74 uint32le :dram_tpr12, :initial_value => 0                    # 0x78 uint32le :dram_tpr13, :initial_value => 0                    # 0x7C uint32le :dram_size, :initial_value => (1024 << 20)          # 0x80,  1024 MB  array    :reserved, :type => :uint32le, :initial_length => 95 # 0x84
 * 1) You need four files from LiveSuit image: fes_1-1.fex, fes_1-2.fex, fes.fex, fes_2.fex
 * 2) Write DRAM config at 0x7010 (180(sun4i and older) or 512 bytes (sun6i+))
 * 3) Write fes_1-1.fex at 0x7210
 * 4) Execute code at 0x7220
 * 5) Write fes_1-2.fex at 0x2000
 * 6) Execute code at 0x2000
 * 7) Write fes.fex at 0x40200000
 * 8) Write fes_2.fex at 0x7220
 * 9) Execute code at 0x7220

Banner
FES mode has a nice ASCII banner printed out on uart (boot 1.0 only)  [FES]:================================================================================================= [FES]:=                                                                                              = [FES]:=                                        EEMMMMMMLL                                            = [FES]:=                                    ::MMMHOLIGANEE                                            = [FES]:=                                  ::MM. = [FES]:=                                  MMFF                                                        = [FES]:=                                FFMM                                                          = [FES]:=                               MMMM                                                           = [FES]:=                             ..MMFF                                                           = [FES]:=                             EEMM. FFMMMM          = [FES]:=. MMMMMMMM   MMMMMMMMMMMMMMMMMM      FFMMMMMM::      ::MMMM      BBMMMMFF           = [FES]:=       ::MM. MMMM         MMMM            MM.   MMMMMM    EE..EEMM::  EE::                 = [FES]:=       MM      MMMM        ::MMLL          EEMM    MMMMFF. MMMM::::                  = [FES]:=     MMMM    FFMMI         BBMM            MMI     MMMM            MMMMEE                     = [FES]:=     MMMM. MM::         MMMM          MMMM    BBMM              MMMM                       = [FES]:=   BBMMFF::EE              MMMM          MMMM  MM::                BBMM.. = [FES]:=   MMMMEE                I MMI         I MMMM::                  ::FFMMFF                     = [FES]:=   MMMM          LL      MMMM          EEMMMM        LL          BB  MMMM                     = [FES]:=   MMMM      I MM        MMMM          MMMMMM      MM::        MM    MMMM                     = [FES]:=   MMMMMMMMMMEE          MMMM          .GUANLI@HUANG. BB   BB      FFMM. = [FES]:=     MMMMMM.. I MMI            MMMMMMEE      MMMMMM          MMEE                   = [FES]:=                       MMMM                                            MMMM                   = [FES]:=                       MMMM                                            ::MM::                 = [FES]:=                       MM                                                BBMM        MM       = [FES]:=                     EEBB                                                  BBMM.. MMMM      = [FES]:=                     MM                                                      ..EEMMFF         = [FES]:=         MMMMMMMMMMMM                                                                         = [FES]:=         MMMMMMMMI                                                                            = [FES]:=                                                                                              = [FES]:=================================================================================================