Hardware modding - UART

[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 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:WRON 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+ ([email protected]) (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

 

[pelago]

Very interesting. Please keep us updated regarding your progress. It would be great to have the TF701T as a "real" Linux machine.

 

[Trel725]

I'd like use foul language... My UART died... I used Chinese usb-uart adapter, it died and killed tablet's uart. :crying: I have no idea. Tablet works fine, but I cannot continue porting linux. I'm sorry.