Mt65xx Preloader — ((free))

MT65xx Preloader Guide 1. What is the Preloader?

The first code executed by the MediaTek boot ROM (BootROM) after power-on. Resides in the internal bootable partition (eMMC/NAND) or sometimes masked ROM. Responsible for initializing DRAM, clock, storage, and loading the next stage (LK – Little Kernel / U-Boot). Also implements DA (Download Agent) protocol for SP Flash Tool communication.

2. Key Characteristics

Vendor : MediaTek File name in firmware: preloader_<project>.bin Size : Typically 64KB – 512KB Load address : Usually 0x200000 or 0x800000 (depends on chip) Signature : Starts with a specific header (e.g., MTK magic, or plain ARM/Thumb code) mt65xx preloader

3. Preloader Functions | Function | Description | |----------|-------------| | DRAM init | Configures memory controller & timing | | Clock/PLL setup | Sets CPU, bus, and peripheral clocks | | Storage init | Initializes eMMC/SD/NAND controller | | Boot device selection | Chooses boot source (eMMC, SD card, USB) | | USB detection | Listens for USB handshake to enter download mode | | Security check | Verifies signatures (if secure boot enabled) | | Load next stage | Loads LK (bootloader) into DRAM & jumps | 4. Identifying Preloader in a Firmware Dump Look for:

Offset 0x00 – ARM exception vectors (reset: ldr pc, [pc,#...] ). Strings like "MTK" , "DA" , "PRELOADER" , "USB" , "DownloadAgent" . Header pattern (some variants): 0x00: 0x4D 0x54 0x4B 0x?? (MTK)

Use binwalk or strings : binwalk preloader.bin strings preloader.bin | head -20 MT65xx Preloader Guide 1

5. Dumping/Backup Preloader (from device) Requires root and SP Flash Tool readback or dd : # Find preloader partition (eMMC) cat /proc/partitions ls -l /dev/block/platform/*/by-name/ Dump using dd (example) dd if=/dev/block/mmcblk0boot0 of=preloader.bin bs=1M count=1 Or from full flash dump dd if=full_dump.bin of=preloader.bin bs=512 count=1024 skip=<partition_offset>

6. Flashing Preloader (SP Flash Tool) Warning : Incorrect preloader can hard-brick (no USB, no boot).

Use SP Flash Tool → Download tab → select PRELOADER scatter entry. Check "DA DL All With Checksum" . DO NOT flash wrong preloader version or from different project. Resides in the internal bootable partition (eMMC/NAND) or

For recovery (dead boot):

Use SP Flash Tool with "Format All + Download" (last resort). Or use MTK Bypass Utility (for auth & brom mode).