Replicant

h2. Introduction

This page contains information on how to work on a bootloader replacement.

h2. Informations

* The "official u-boot source code":http://git.denx.de/cgi-bin/gitweb.cgi?p=u-boot.git;a=summary already has support for the S5PC110 SOC(system on a chip) that the Nexus S uses

* The S5PC110 has a bootrom

* The Nexus S has an usb port with an FSA9480 behind it

h2. Links of interest

* "Create your own I9000/S8500 (& all S5PC110 based devices) bootloader&ultimate unbrick - XDA-Developers Forums":http://forum.xda-developers.com/showthread.php?t=1233273

* "HOW-TO [[UnBrick]] the [[UnBrickable]] Vibrant - xda-developers":http://forum.xda-developers.com/showthread.php?t=1277056

* "Boot sequence interception/redirection for Hummingbird processors":http://code.google.com/p/hummingbird-hibl/

* "source code for hummingbird-hibl":http://code.google.com/p/hummingbird-hibl/source/browse/trunk/HummingBirdInterceptorBootloader/

* "Unbrick Your Hummingbird-Powered Device by Creating Your Own Bootloader":http://www.xda-developers.com/android/unbrick-your-hummingbird-powered-device-by-creating-your-own-bootloader/

* "Create your own I9000/S8500 (& all S5PC110 based devices) bootloader&ultimate unbrick":http://forum.xda-developers.com/showthread.php?t=1233273

h3. Partitioning informations

<pre>

Entry Count: 16

Unknown 1: 0

Unknown 2: 0

Unknown 3: 0

Unknown 4: 0

Unknown 5: 0

Unknown 6: 0

Unknown 7: 0

Unknown 8: 0

--- Entry #0 ---

Unused: No

Partition Type: 0 (RFS)

Partition Identifier: 0

Partition Flags: 0 (R)

Unknown 1: 0

Partition Block Size: 256

Partition Block Count: 1

Unknown 2: 0

Unknown 3: 0

Partition Name: IPBL

Filename: bootloader.img

--- Entry #1 ---

Unused: No

Partition Type: 0 (RFS)

Partition Identifier: 1

Partition Flags: 0 (R)

Unknown 1: 0

Partition Block Size: 256

Partition Block Count: 7

Unknown 2: 0

Unknown 3: 0

Partition Name: SBL

Filename: 

--- Entry #2 ---

Unused: No

Partition Type: 0 (RFS)

Partition Identifier: 2

Partition Flags: 0 (R)

Unknown 1: 0

Partition Block Size: 256

Partition Block Count: 7

Unknown 2: 0

Unknown 3: 0

Partition Name: SBL2

Filename: 

--- Entry #3 ---

Unused: No

Partition Type: 0 (RFS)

Partition Identifier: 3

Partition Flags: 0 (R)

Unknown 1: 0

Partition Block Size: 256

Partition Block Count: 4

Unknown 2: 0

Unknown 3: 0

Partition Name: PARAM

Filename: 

--- Entry #4 ---

Unused: No

Partition Type: 0 (RFS)

Partition Identifier: 4

Partition Flags: 0 (R)

Unknown 1: 0

Partition Block Size: 256

Partition Block Count: 5

Unknown 2: 0

Unknown 3: 0

Partition Name: MISC

Filename: 

--- Entry #5 ---

Unused: No

Partition Type: 0 (RFS)

Partition Identifier: 5

Partition Flags: 0 (R)

Unknown 1: 0

Partition Block Size: 256

Partition Block Count: 32

Unknown 2: 0

Unknown 3: 0

Partition Name: BOOT

Filename: boot.img

--- Entry #6 ---

Unused: No

Partition Type: 0 (RFS)

Partition Identifier: 6

Partition Flags: 0 (R)

Unknown 1: 0

Partition Block Size: 256

Partition Block Count: 32

Unknown 2: 0

Unknown 3: 0

Partition Name: RECOVERY

Filename: recovery.img

--- Entry #7 ---

Unused: No

Partition Type: 0 (RFS)

Partition Identifier: 7

Partition Flags: 1 (R)

Unknown 1: 0

Partition Block Size: 256

Partition Block Count: 1878

Unknown 2: 0

Unknown 3: 0

Partition Name: CACHE

Filename: cache.img

--- Entry #8 ---

Unused: Yes

Partition Type: 0 (RFS)

Partition Identifier: 8

Partition Flags: 0 (R)

Unknown 1: 0

Partition Block Size: 256

Partition Block Count: 54

Unknown 2: 0

Unknown 3: 0

Partition Name: RADIO

Filename: radio.img

--- Entry #9 ---

Unused: No

Partition Type: 0 (RFS)

Partition Identifier: 9

Partition Flags: 1 (R)

Unknown 1: 0

Partition Block Size: 256

Partition Block Count: 27

Unknown 2: 0

Unknown 3: 0

Partition Name: EFS

Filename: 

--- Entry #10 ---

Unused: No

Partition Type: 0 (RFS)

Partition Identifier: 10

Partition Flags: 0 (R)

Unknown 1: 0

Partition Block Size: 256

Partition Block Count: 1

Unknown 2: 0

Unknown 3: 0

Partition Name: DGS

Filename: dgs.img

--- Entry #11 ---

Unused: No

Partition Type: 2 (EXT4)

Partition Identifier: 0

Partition Flags: 2 (R/W)

Unknown 1: 0

Partition Block Size: 512

Partition Block Count: 2048

Unknown 2: 0

Unknown 3: 0

Partition Name: PGPT

Filename: emmc.img

--- Entry #12 ---

Unused: No

Partition Type: 2 (EXT4)

Partition Identifier: 1

Partition Flags: 2 (R/W)

Unknown 1: 0

Partition Block Size: 512

Partition Block Count: 1048576

Unknown 2: 0

Unknown 3: 0

Partition Name: SYSTEM

Filename: system.img

--- Entry #13 ---

Unused: No

Partition Type: 2 (EXT4)

Partition Identifier: 2

Partition Flags: 2 (R/W)

Unknown 1: 0

Partition Block Size: 512

Partition Block Count: 2097152

Unknown 2: 0

Unknown 3: 0

Partition Name: USERDATA

Filename: userdata.img

--- Entry #14 ---

Unused: No

Partition Type: 2 (EXT4)

Partition Identifier: 3

Partition Flags: 2 (R/W)

Unknown 1: 0

Partition Block Size: 512

Partition Block Count: 33554432

Unknown 2: 0

Unknown 3: 0

Partition Name: MEDIA

Filename: media.img

--- Entry #15 ---

Unused: No

Partition Type: 2 (EXT4)

Partition Identifier: 4

Partition Flags: 2 (R/W)

Unknown 1: 0

Partition Block Size: 512

Partition Block Count: 33

Unknown 2: 0

Unknown 3: 0

Partition Name: SGPT

Filename: 

</pre>

h2. Serial Console

It is possible to setup a serial console on the Nexus S. It will show:

* the 1st bootloader output

* the 2nd bootloader output

* the 2nd bootloader #2 output

* the fiq debugger

* (the kernel output if enabled)

h3. How to enable serial console

* completely turn off the Nexus S

* attach the microUSB connector to the Nexus S

* wire GND and ID (from the microUSB connector) to a 150K resistor

* get an UART to USB module like this one: http://www.dealextreme.com/p/usb-to-uart-5-pin-cp2102-module-serial-converter-81872

* wire it following this table:

|_. UART to USB board output |_. Resistor |_. microUSB connector(s) name(s) |_. microUSB wire color |

| N/A | 150K Ohm | ID and GND | ID not wired (the 5th connector that is unused), GND is black |

| 3.3V | N/A | V+ | red |

| GND | N/A | GND | black |

| Rx | N/A | D- | white |

| Tx | N/A | D+ | green |

*Warning: the voltage to use is 3.3V and not 5V! Using 5V can cause serious damages to the UART component.*

To read/write on the serial, you can use screen (or picocomm, or any other software that deals with serial consoles):

115200 is the baud rate to use (certainly with most UART to USB board). 

Then, do a regular boot. You should see the second bootloader #2 output. To get the 1st and 2nd bootloaders output, press <enter> to get in fiq debugger and write "reboot" then <enter>.

Photos: here's what it looks like when all setup:

!http://redmine.replicant.us/attachments/93/serial_1145.jpeg!

!http://redmine.replicant.us/attachments/99/serial_1150.JPG!

!http://redmine.replicant.us/attachments/105/serial_1151.jpeg!

!http://download.paulk.fr/replicant/crespo/uart/uart_board.jpg!

The UART to USB board. USB is connected to the host PC, UART pins to the microUSB connector.

!http://download.paulk.fr/replicant/crespo/uart/nexuss_resistor.jpg!

The 150K resistor (two resistors here that make 150K together) soldered to the microUSB connector, that is attached to the Nexus S.

_Note: it was done the quick and dirty way here, it's better to use a protoboard (prototyping board)._ 

!http://download.paulk.fr/replicant/crespo/uart/nexuss_global_text.jpg!

The USB cable that is connected to the Nexus S ends on the connectors attached to the UART to USB board.

_Note: it was done the quick and dirty way here, it's better to use a protoboard (prototyping board)._ 

h3. Bootloaders outputs

first bootloader:

<pre>

-----------------------------------------------------------

   Samsung Primitive Bootloader (PBL) v3.0

   Copyright (C) Samsung Electronics Co., Ltd. 2006-2010

-----------------------------------------------------------

Muxed [[OneNAND]] 512MB (0x50) Sync

Scanning Bad Block .......

Bad Block 77 (5)

Bad Block 295 (5)

Bad Block 1232 (5)

Bad Block 1646 (5)

Bad Block 1831 (5)

Bad Block 2047 (0)

SBL loadding success

Set cpu clk. from 400MHz to 800MHz.

OM=0x9, device=OnenandMux(Audi)

IROM e-fused - Secure Boot Version.

</pre>

second bootloader:51ea3aaa63e65b74b7386fe1365d7b52f4495c43

<pre>

-----------------------------------------------------------

   Samsung Secondary Bootloader (SBL) v3.0

   Copyright (C) Samsung Electronics Co., Ltd. 2006-2010

   Board Name: HERRING REV 52

   Build On: Jan 20 2011 17:19:41

-----------------------------------------------------------

MMC SEM16G 15188 MB

Re_partition: magic code(0x0)

Muxed [[OneNAND]] 512MB (0x50) Sync

Scanning Bad Block .......

Bad Block 77 (5)

Bad Block 295 (5)

Bad Block 1232 (5)

Bad Block 1646 (5)

Bad Block 1831 (5)

Bad Block 2047 (0)

Partitions loading success

Read image(PARAM) from flash .......

Done

init_fuel_gauge: vcell = 4083mV, soc = 94

PMIC_IRQ1    = 0xc0 

PMIC_IRQ2    = 0x0 

PMIC_IRQ3    = 0x0 

PMIC_IRQ4    = 0x0 

PMIC_STATUS1 = 0x0 

PMIC_STATUS2 = 0x0 

PMIC_STATUS3 = 0x0 

PMIC_STATUS4 = 0x0 

PMIC_STATUS5 = 0x0 

PMIC_SMPL    = 0x0 

Key scan = 0x0

message.command = 

message.status = 

message.recovery = 

</pre>

second bootloader #2:

<pre>

BOOT_MODE_NORMAL (SW_RST(0x00000004), INFORM(0x000000ee))

LCD ID = 0x0060a953

Done

Kernel(boot.img) read success from partition no.5

Setting param.serialnr = 0x3733bab6 0x6de200ec

Setting param.board_rev = 0x34

Setting param.cmdline = console=ttyFIQ0 no_console_suspend androidboot.serialno=3733BAB66DE200EC androidboot.bootloader=I9020XXKA3 androidboot.baseband=I9020XXKB3 androidboot.info=0x4,0xee,1 androidboot.carrier=EUR gain_code=3 s3cfb.bootloaderfb=0x34a00000 mach-herring.lcd_type=0x00000000 oem_state=unlocked 

Setting param.initrd_start = 0x31000000, param.initrd_size = 0x23265

Starting kernel at 0x30008000...

Uncompressing Linux... done, booting the kernel.

</pre>

kernel

<pre>

<hit enter to activate fiq debugger>

</pre>

h2. JTAG

Here is the location and the description of the JTAG pins on the Nexus S board:

!http://redmine.replicant.us/attachments/3/jtag-pins.png!

!http://redmine.replicant.us/attachments/9/jtag-pins-desc.png!

JTAG was untested on the device so far. 

h2. Conclusions

* Heimdall mode is accessible but we didn't try to flash images with heimdall

* Serial can be set up and works

* The bootrom(IROM) seems signed: <pre>IROM e-fused</pre>

* JTAG is there but we didn't try it

*As the IROM is apparently signed, porting a free bootloader will most likely fail as Primary Boot Loader (PBL).*