Bootloaders for RB5 & RB3 (Dev Kit from Qualcomm)

RB5 Bootflow from Link

In this article,We would talk about boot flow on qualcomm chipsets like RB5 Dev Kit and would like to understand what all initialization it covers and do some hands-on with Android Boootloaders (ABL) for qualcomm chipsets including RB3 GEN 2 boot flow also.

The ABL comes as third stage boot loaders as shown in following diagram whose main objective is to boot the OS like Linux for Android based system.

Stages of Boot FLows in RB5

The ABL for RB5 is based on UEFI EDK2 source code which has typical flow (below)for any boot firmwares like Intel BIOS etc.

UEFI Flow explained at Link

The ABL source code is located at Linao Link . Similarly RB3 has systemd-boot manager which works for booting embeeded Linux/Ubuntu (LE or LU) on this Kit. RB3 GEN 2 doesn’t support Android booting as of now.

ABL has specific EDK2 package from Qualcomm to be compiled with and generate abl.elf which get flashed on supported Android Partition.

To build ABL as part of Android build system, Androidboot.mk and makefiles are required which has following invocation to build QcomModulePkg.

Makefiles Integrated in Android Build System

The dsc (description), dec (declaration) , inf (initialization) and fdf (firmware disk flash) files are typical EDK2 artifiacts which describe the source files and relaed configuration for building the current modules as well its dependencies .

As part of EDK2 build process, makefiles are generated ( via AutoGen/GenMake) for each module and then compiled and linked to generate final ABL FV (Firmware Volume) . This FV is nothing but the abl.elf which can be flashed on below abl partition for RB5 using fastboot.

Please comment/correct if there are any misinformations .