Schematics and service manual for i9250: Samsung_i9250_schem_sm.rar 

Contents: [Dobrica Pavlinušić's random unstructured stuff]
• Dobrica Pavlinušić's random unstructured stuff (BLE) 
• Dobrica Pavlinušić's random unstructured stuff (GSM modem over serial port) 
• Dobrica Pavlinušić's random unstructured stuff (HID keyboard) 
• Dobrica Pavlinušić's random unstructured stuff (Unlegacy Android) 
• Dobrica Pavlinušić's random unstructured stuff (kernel) 
• Dobrica Pavlinušić's random unstructured stuff (OMAP4 USB boot) 
• Dobrica Pavlinušić's random unstructured stuff (Odin) 
• Dobrica Pavlinušić's random unstructured stuff (serial) 
• Dobrica Pavlinušić's random unstructured stuff (UART modes) 
• Dobrica Pavlinušić's random unstructured stuff (PostmarketOS) 
• Dobrica Pavlinušić's random unstructured stuff (u‑boot) 

127|root@maguro:/ # cat /proc/cpuinfo                                          
Processor       : ARMv7 Processor rev 10 (v7l)
processor       : 0
BogoMIPS        : 1194.24

processor       : 1
BogoMIPS        : 1194.24

Features        : swp half thumb fastmult vfp edsp thumbee neon vfpv3 
CPU implementer : 0x41
CPU architecture: 7
CPU variant     : 0x2
CPU part        : 0xc09
CPU revision    : 10

Hardware        : Tuna
Revision        : 0009
Serial          : 014994b30201c013

BLE
• https://github.com/metc/galaxy‑nexus‑ble 
GSM modem over serial port
• https://github.com/2b‑as/xgoldmon 
HID keyboard
• https://github.com/pelya/android‑keyboard‑gadget 
Unlegacy Android
ASOP for OMAP4 devices:
https://forum.xda‑developers.com/galaxy‑nexus/development/rom‑omap4‑aosp‑project‑t3334574 
https://github.com/Unlegacy‑Android/ 
kernel
http://unlegacy‑android.cf/ 
https://github.com/Unlegacy‑Android/android_kernel_samsung_tuna 
dpavlin@klin:/virtual/android/galaxy-nexus$ git clone https://android.googlesource.com/platform/prebuilts/gcc/linux-x86/arm/arm-eabi-4.8/

dpavlin@klin:/virtual/android/galaxy-nexus/omap$ git checkout -b asop-7.1 unlegacy/aosp-7.1

dpavlin@klin:/virtual/android/galaxy-nexus/omap$ make tuna_defconfig ARCH=arm

dpavlin@klin:/virtual/android/galaxy-nexus/omap$ cp include/linux/compiler-gcc4.h include/linux/compiler-gcc5.h

dpavlin@klin:/virtual/android/galaxy-nexus/omap$ make -j9 ARCH=arm CROSS_COMPILE=arm-none-eabi-

OMAP4 USB boot
Somewhat interesting things that I can take a look at some time in the future:
• https://github.com/swetland/omap4boot 
• newer(ish) version is on https://github.com/dmitry‑pervushin/usbboot‑omap4 
To compile it needs following change:
dpavlin@nuc:/nuc/Galaxy-Nexus-i9250/usbboot-omap4$ git diff
diff --git a/Makefile b/Makefile
index 2d10c73..9ea9461 100644
--- a/Makefile
+++ b/Makefile
@@ -38,7 +38,7 @@ BINDIR ?= $(DESTDIR)/usr/bin
 DATADIR ?= $(DESTDIR)/usr/share/usbboot
 DOCDIR ?= $(DESTDIR)/usr/share/doc/usbboot
 
-BOARD ?= panda
+BOARD ?= tuna
 
 TARGET_CC := $(TOOLCHAIN)gcc
 TARGET_LD := $(TOOLCHAIN)ld
diff --git a/tools/usb-linux.c b/tools/usb-linux.c
index e3492a1..09c40de 100755
--- a/tools/usb-linux.c
+++ b/tools/usb-linux.c
@@ -10,7 +10,7 @@ int linux_usb_init(void)
        r = libusb_init(&ctx);
        if (r != 0)
                return r;
-       libusb_set_debug(ctx,0x1);
+       //libusb_set_debug(ctx,0x1);
     return 0;
 }

Odin
• http://glassechidna.com.au/heimdall/ 
serial
• https://wiki.postmarketos.org/wiki/Serial_debugging#USB_debug_cable 

Device	Codename	Resistor (R3)	Connected VCC	
Google Galaxy Nexus (GSM)	samsung‑maguro	619K ohm	No	
Samsung Galaxy Mini 2	samsung‑s6500d	530K ohm	No	
Samsung Galaxy S4 Mini LTE	samsung‑i9195	619K ohm	No	
Samsung Galaxy S5	samsung‑klte	619K ohm	No	

It seems that other suggestion is 150k from https://redmine.replicant.us/projects/replicant/wiki/SamsungSerial  ‑ I will have to test which value works
UART modes
• https://wiki.postmarketos.org/wiki/Micro‑USB_Interface_Controller 

Resistance	Jig	Boot	
150k	Inactive	Inactive	
523k	Active	Inactive	
619k	Active	Active	

RID_USB_OTG_MODE,       /* 0 0 0 0 0    GND             USB OTG Mode              */
RID_AUD_SEND_END_BTN,   /* 0 0 0 0 1    2K              Audio Send_End Button*/
RID_AUD_REMOTE_S1_BTN,  /* 0 0 0 1 0    2.604K          Audio Remote S1 Button */
RID_AUD_REMOTE_S2_BTN,  /* 0 0 0 1 1    3.208K          Audio Remote S2 Button                         */
RID_AUD_REMOTE_S3_BTN,  /* 0 0 1 0 0    4.014K          Audio Remote S3 Button */
RID_AUD_REMOTE_S4_BTN,  /* 0 0 1 0 1    4.82K           Audio Remote S4 Button */
RID_AUD_REMOTE_S5_BTN,  /* 0 0 1 1 0    6.03K           Audio Remote S5 Button */
RID_AUD_REMOTE_S6_BTN,  /* 0 0 1 1 1    8.03K           Audio Remote S6 Button */
RID_AUD_REMOTE_S7_BTN,  /* 0 1 0 0 0    10.03K          Audio Remote S7 Button */
RID_AUD_REMOTE_S8_BTN,  /* 0 1 0 0 1    12.03K          Audio Remote S8 Button */
RID_AUD_REMOTE_S9_BTN,  /* 0 1 0 1 0    14.46K          Audio Remote S9 Button */
RID_AUD_REMOTE_S10_BTN, /* 0 1 0 1 1    17.26K          Audio Remote S10 Button */
RID_AUD_REMOTE_S11_BTN, /* 0 1 1 0 0    20.5K           Audio Remote S11 Button */
RID_AUD_REMOTE_S12_BTN, /* 0 1 1 0 1    24.07K          Audio Remote S12 Button */
RID_RESERVED_1,         /* 0 1 1 1 0    28.7K           Reserved Accessory #1 */
RID_RESERVED_2,         /* 0 1 1 1 1    34K             Reserved Accessory #2 */
RID_RESERVED_3,         /* 1 0 0 0 0    40.2K           Reserved Accessory #3 */
RID_RESERVED_4,         /* 1 0 0 0 1    49.9K           Reserved Accessory #4 */
RID_RESERVED_5,         /* 1 0 0 1 0    64.9K           Reserved Accessory #5 */
RID_AUD_DEV_TY_2,       /* 1 0 0 1 1    80.07K          Audio Device Type 2 */
RID_PHONE_PWD_DEV,      /* 1 0 1 0 0    102K            Phone Powered Device */
RID_TTY_CONVERTER,      /* 1 0 1 0 1    121K            TTY Converter */
RID_UART_CABLE,         /* 1 0 1 1 0    150K            UART Cable */
RID_CEA936A_TY_1,       /* 1 0 1 1 1    200K            CEA936A Type-1 Charger(1) */
RID_FM_BOOT_OFF_USB,    /* 1 1 0 0 0    255K            Factory Mode Boot OFF-USB */
RID_FM_BOOT_ON_USB,     /* 1 1 0 0 1    301K            Factory Mode Boot ON-USB */
RID_AUD_VDO_CABLE,      /* 1 1 0 1 0    365K            Audio/Video Cable */
RID_CEA936A_TY_2,       /* 1 1 0 1 1    442K            CEA936A Type-2 Charger(1) */
RID_FM_BOOT_OFF_UART,   /* 1 1 1 0 0    523K            Factory Mode Boot OFF-UART */
RID_FM_BOOT_ON_UART,    /* 1 1 1 0 1    619K            Factory Mode Boot ON-UART */
RID_AUD_DEV_TY_1_REMOTE, /* 1 1 1 1 0   1000.07K        Audio Device Type 1 with Remote(1) */
RID_AUD_DEV_TY_1_SEND = RID_AUD_DEV_TY_1_REMOTE , /* 1 1 1 1 0  1002K           Audio Device Type 1 / Only Send-End(2) */
RID_USB_MODE,           /* 1 1 1 1 1    Open            USB Mode, Dedicated Charger or Accessory Detach */

PostmarketOS
dpavlin@nuc:/nuc/pmbootstrap$ ./pmbootstrap.py install --no-fde
[17:54:17] *** (1/5) PREPARE NATIVE CHROOT ***
[17:54:18] *** (2/5) CREATE DEVICE ROOTFS ("samsung-maguro") ***
[17:54:23] (rootfs_samsung-maguro) install
[17:54:27] (rootfs_samsung-maguro) install
[17:54:30] (rootfs_samsung-maguro) write /etc/os-release
[17:54:30] (rootfs_samsung-maguro) mkinitfs samsung-maguro
[17:54:34]  *** SET LOGIN PASSWORD FOR: 'dpavlin' ***
New password:
Retype new password:
passwd: password updated successfully
[17:54:43] NOTE: No valid keymap specified for device
[17:54:46] *** (3/5) PREPARE INSTALL BLOCKDEVICE ***
[17:54:47] (native) create samsung-maguro.img (361M)
[17:54:47] (native) mount /dev/install (samsung-maguro.img)
[17:54:47] (native) partition /dev/install (boot: 31M, root: the rest)
[17:54:47] (native) format /dev/installp2
[17:54:48] (native) mount /dev/installp2 to /mnt/install
[Tue Sep 25 17:55:21 2018] EXT4-fs (loop0p2): mounted filesystem with ordered data mode. Opts: (null)
[17:54:48] (native) format /dev/installp1 (boot, ext2), mount to /mnt/install/boot
[Tue Sep 25 17:55:21 2018] EXT4-fs (loop0p1): mounting ext2 file system using the ext4 subsystem
[Tue Sep 25 17:55:21 2018] EXT4-fs (loop0p1): mounted filesystem without journal. Opts: (null)
[17:54:48] *** (4/5) FILL INSTALL BLOCKDEVICE ***
[17:54:48] (native) copy rootfs_samsung-maguro to /mnt/install/
[17:54:53] *** (5/5) FLASHING TO DEVICE ***
[17:54:53] Run the following to flash your installation to the target device:
[17:54:53] * pmbootstrap flasher flash_rootfs
[17:54:53]   Flashes the generated rootfs image to your device:
[17:54:53]   /nuc/pmbootstrap-work/chroot_native/home/pmos/rootfs/samsung-maguro.img
[17:54:53]   (NOTE: This file has a partition table, which contains /boot and / subpartitions. That way we don't need to change the partition layout on your device.)
[17:54:53] * pmbootstrap flasher flash_kernel
[17:54:53]   Flashes the kernel + initramfs to your device:
[17:54:53]   /nuc/pmbootstrap-work/chroot_rootfs_samsung-maguro/boot
[17:54:53]   (NOTE: fastboot also supports booting the kernel/initramfs directly without flashing. Use 'pmbootstrap flasher boot' to do that.)
[17:54:53] * If the above steps do not work, you can also create symlinks to the generated files with 'pmbootstrap export' and flash outside of pmbootstrap.
[17:54:53] NOTE: chroot is still active (use 'pmbootstrap shutdown' as necessary)
[17:54:53] Done

dpavlin@nuc:/nuc/pmbootstrap$ alias pmbootstrap=/nuc/pmbootstrap/pmbootstrap.py
dpavlin@nuc:/nuc/pmbootstrap$ pmbootstrap flasher flash_rootfs
[17:57:10] (native) flash rootfs image
< waiting for any device >
[Tue Sep 25 17:59:17 2018] usb 2-3.1: new high-speed USB device number 22 using xhci_hcd
[Tue Sep 25 17:59:17 2018] usb 2-3.1: New USB device found, idVendor=18d1, idProduct=4e30, bcdDevice= 1.00
[Tue Sep 25 17:59:17 2018] usb 2-3.1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[Tue Sep 25 17:59:17 2018] usb 2-3.1: Product: Android 1.0
[Tue Sep 25 17:59:17 2018] usb 2-3.1: Manufacturer: Google, Inc
[Tue Sep 25 17:59:17 2018] usb 2-3.1: SerialNumber: 014994B00C01A013
target didn't report max-download-size
Erasing 'system'...
OKAY [  0.047s]
Sending 'system' (369664 KB)...
OKAY [ 50.498s]
Writing 'system'...
OKAY [ 26.436s]
Finished. Total time: 77.024s
[18:00:02] NOTE: chroot is still active (use 'pmbootstrap shutdown' as necessary)
[18:00:02] Done
dpavlin@nuc:/nuc/pmbootstrap$ [Tue Sep 25 19:24:27 2018] usb 2-3.1: USB disconnect, device number 22
[Tue Sep 25 19:24:27 2018] usb 2-3.1: new high-speed USB device number 23 using xhci_hcd
[Tue Sep 25 19:24:27 2018] usb 2-3.1: unable to get BOS descriptor
[Tue Sep 25 19:24:27 2018] usb 2-3.1: New USB device found, idVendor=0451, idProduct=d010, bcdDevice= 0.00
[Tue Sep 25 19:24:27 2018] usb 2-3.1: New USB device strings: Mfr=33, Product=37, SerialNumber=0
[Tue Sep 25 19:24:27 2018] usb 2-3.1: Product: OMAP4440
[Tue Sep 25 19:24:27 2018] usb 2-3.1: Manufacturer: Texas Instruments
[Tue Sep 25 19:24:30 2018] usb 2-3.1: USB disconnect, device number 23

u‑boot
• https://github.com/Ksys‑labs/uboot‑tuna