[Asus Transformer TF701] Trel725:
I'm porting Linux to tf701t, and I need any debugging tool. The most multipurpose is UART, universal asynchrony receiver-transmitter. That is COM-port like in old PC. There is difference between PC serial port and tablet UART, different voltage. Therefore adapter is necessary. I just bought usb-uart adapter.

Uart consist of 4 pins - ground, tx, rx, power. Power is not necessary, ground is metal back of tablet or any connector. I had to find tx and (optionally) rx. I teared down my tablet, but there were nothing like uart pins. Then, I tear off copper foil, isolation, and found a lot of pins

Next I tried every pin, and finally found the tx and rx nearby. Rx works strange I don't know why.

I soldered wire to tx pin, and covered by isolation.

I couldn't solder rx because I used Old Big Soldering:

I'm crazy :D But all right.

UART is very useful. For example, the piece of boot log:

NVRM Initialized shmoo database

NVRM CLOCKS: PLLX0: 696000 Khz

NVRM CLOCKS: PLLM0: 792000 Khz

NVRM CLOCKS: PLLC0: 0 Khz

NVRM CLOCKS: PLLP0: 408000 Khz

NVRM CLOCKS: PLLA0: 11289 Khz

NVRM CLOCKS: CPU: 696000 Khz

NVRM CLOCKS: AVP: 102000 Khz

NVRM CLOCKS: System Bus: 102000 Khz

NVRM CLOCKS: Memory Controller: 792000

NVRM CLOCKS: External Memory Controller: 792000

Tps65914ReadVersions() Internal DesignRev 0xbc, SWRev 0x03

Tps65914ReadVersions(): ES version 2.2: ChipRevision 0xb2bc

Tps65914PmuDriverOpen(): The smps123 current is 12000

Tps65914PmuDriverOpen(): The smps45/smps457 current is 8000

ADJUSTED CLOCKS:

MC clock is set to 792000 KHz

EMC clock is set to 792000 KHz (DDR clock is at 792000 KHz)

PLLX0 clock is set to 696000 KHz

PLLC0 clock is set to 0 KHz

CPU clock is set to 696000 KHz

System and AVP clock is set to 102000 KHz

GraphicsHost clock is set to 163200 KHz

3D clock is set to 132000 KHz

2D clock is set to 132000 KHz

Epp clock is set to 132000 KHz

MSENC clock is set to 132000 KHz

Vde clock is set to 204000 KHz

Bootloader-Cpu Init at: 1321837 us

Pi[1620] TPS65914::Int1_Status - 0x00000002

[1624] TPS65914::Int2_Status - 0x00000000

[1628] TPS659nmux changes applied in kernel way

[bootloader] (built on Jul 11 2014, 20:25:19)

Platform Pre Boot configuratio14::Int3_Status - 0x00000000

[1641] TPS65914::Int4_Status - 0x00000000

[1645] TPS65914::PWRON DETECTED

n...

NvOdmQueryGetBoardModuleInfo(): Maximum Core current 8000

XUSBH WARNING: NvDdkXusbhBlockDevInit : Either device is not connected or not enumerated

Initializing Display

project is MOZARTN or HAYDN, get battery capacity from 0x17 address

I2C success

Pget battery capacity: ROM mode status: 0

real battery capacity = 12

Show xhdpi logo

show logo at 2388ms

Verify chip uid

chip uid Unlock RSAVerify ok

The Device is UnLocked.

[bootloader] (built on Jul 11 2014, 20:25:19)

Verify chip uid

chip uid Unlock RSAVerify ok

Device - Unlocked

Serial Number 15C3E1008000000000B030380

Checking for android ota recovery

Key driver not found.. Booting OS

Cold-booting Linux

Platform Pre OS Boot configuration...

Actual Size = 0x45b000 bytes

The device is fused!!

Verify chip uid

chip uid Unlock RSAVerify ok

HasValidDtbImage: Invalid fdt header. err: FDT_ERR_BADMAGIC

Machine Mozart was detected

TSEC OTF key generation process started

OTF key is successfully generated and Unencrypted key is written to VDE

PKC Warmboot Signing Verification success

The proc BoardInfo: 0x0621:0x03ea:0x00:0x43:0x03

NvOdmQueryGetBoardModuleInfo(): Maximum Core current 8000

asustek.hw_rev=rev_b

androidboot.productid=mozart

The device is fused!!

Verify chip uid

chip uid Unlock RSAVerify ok

XUSB Firmware has been loaded successfully...

Board Id Read Time: 0 us

Power Rail enable Time: 39108 us

Bootloader (AosInit) time: 181145 us

BlockDevMgrInit time: 26051 us

PartMgrInit time: 3 us

StorMgrInit time: 11 us

FsMgrInit time: 1 us

Display init time: 422597 us

Kernel read time: 102 msec

Load Kernel Size: 4567040 Bytes

Bl Kernel ReadSpeed: 44774000 Bytes/sec

Pre-Kernel Jump time: 2909389 us

Jumping to kernel at: 2942666 us

[ 0.000000] Booting Linux on physical CPU 0

[ 0.000000] Initializing cgroup subsys cpu

[ 0.000000] Linux version 3.4.104-cyanogenmod+ (build02@cyanogenmod) (gcc version 4.7 (GCC) ) #1 SMP PREEMPT Wed Oct 8 08:14:40 PDT 2014

[ 0.000000] CPU: ARMv7 Processor [412fc0f2] revision 2 (ARMv7), cr=10c5387d

[ 0.000000] CPU: PIPT / VIPT nonaliasing data cache, PIPT instruction cache

[ 0.000000] Machine: mozart