Differences

This shows you the differences between two versions of the page.

--- boot [2012/01/03 11:42] – Description of the Boot process is added paulf
+++ boot [2012/12/31 20:51] (current) – marvin24
@@ Line 4: / Line 4: @@
-[[fastboot|Fastboot]]
+[[fastboot|Fastboot]] is the Android's bootloader, requires non-standard partitioning scheme, see below
 [[uboot|uboot]]
@@ Line 13: / Line 13: @@
 [[swarren_brain_dump]] explains a lot about how the device boots from eMMC
+[[fat_installer|Fat installer]] collects ideas how to painless migrate to u-boot.
 ====== Boot Process ======
-This explanation is based on http://www.muromec.org.ua/2011/03/blog-post.html
+This explanation is based on http://www.muromec.org.ua/2011/03/blog-post.html, and updated by swarren.
-  * After power-on, a ROM bootloader (RCM?) integrated in Tegra2 IC starts
+  * After power-on, a the embedded controller (EC/NVEC) starts running.
-  * If Ctrl-Esc is pressed (most probably detected via a dedicated line between EC and Tegra), the loader switches to "nvflash" mode (USB 0x0955:0x7820) and starts to receive commands on its mini-USB receptable, [[putusb]] and [[nvflash]] are the tools that can communicate with it in this mode.
+  * If Ctrl-Esc is pressed, the EC signals this to Tegra by pulling a Tegra pin to a specific state, requesting recovery mode.
-  * If the boot is to continue, the bootloader assess some fuse bits settings to see where it should boot from, on ac100 that's internal eMMC.
+  * The EC either powers on Tegra, or releases it from reset.
-  * It searches for BCT on the eMMC and finds EBT (4th) partition there
+  * A ROM bootloader integrated into Tegra IC starts.
-  * Vendors supplies EBT with Fastboot bootloader which then reads an image (in [[abootimg]] format) from the LNX (6th) (or if the "Home" button is pressed SOS (5th)) partition, copies the kernel and initramfs to the approprieate RAM locations and starts it supplying default command line parameters (with ATAGs).
+  * If recovery mode was requested, the ROM bootloader loader switches to RCM (ReCovery Mode) (USB 0x0955:0x7820) and starts to receive commands on its mini-USB receptable, [[putusb]] and [[nvflash]] are the tools that can communicate with it in this mode.
+  * If the boot is to continue, the bootloader assess some fuse bits (and/or strapping pins) to see where it should boot from. On ac100 that's internal eMMC.
+  * It searches for BCT (Boot Config Table) and for PT (Partition Table) on the eMMC and finds EBT (4th) partition there. (swarren: I'm not sure if the bootloader actually uses the PT or not; it may get the bootloader details from fields in the BCT).
+  * Vendors fill EBT with Fastboot bootloader which then reads an image (in [[abootimg]] format) from the LNX (6th) (or if the "Home" button is pressed SOS (5th)) partition, copies the kernel and initramfs to the approprieate RAM locations and starts it supplying default command line parameters (with ATAGs).