How to use the absolute value encoder reasonably base on ethercat?

I've got a server motor with 17bit absolute value encoder which has battery installed and the servo controller has ethercat interface.
The situation is when I power off the machine and change the joint position manully. How can I move the joint to original position.
The machine platform is RPI4 ,ethercat comp is ''github.com/dbraun1981/hal-cia402.git'' use csp-mode. Besides, I can read out the encoder absolute value in pdo addr "0x213C" and "0x213D", encoder user value "0x6064"(will be 0 after power off) .

please give detailed information about pdos
"0x213C" and "0x213D"

is this 64bit position value ?

yes, it is 64bit value. 0x213C is low 32bit signed value and 0x213D is the high 32bit.
And I think I've found the key to the problen. The "drv_target_position 0x607A" shall follow “drv_actual_position” before cspmod enabled. If I use the abs value instead of "drv_actual_position 0x6064". Even I have decrease the abs value to real offset. It is still too long, and it is dangerous operation.So the right operation is change the ini.x.home_offset before homing.But I don't know how to do yet. Any suggestion will be grateful.

can you tell the type of servo drive? manual?

are you shure? or are them two 16bit pdos ?

i have not seen an 64 bit pos register in my life yet...
or is one pdo only for the multiturns?
If you will get an 64bit feedback register, you should also get an 64bit setpoint register.

With 17bit encoder , 32bit pos register should be fine -> that are 12bit of multiturns....

We can use an encoder_class that handels 64 bit values for overflow protection. But the linuxcnc motionpart can only handle 32 bits.

The servo driver made in China and the company named HCFA.I think 32bit reg is enough for normal CNC machine.Actually there is 4 pdo addr 0x213A for multiturns, 0x213B for single turn position, 0x213C and 0x213D as I said above.The relationship of these pdo is [Num_turns(0x213A)*(0x20000) + pos(0x213B) = pos_L(0x213C) + pos_H(0x213D)<<32]. Let's forget this. Now I just want to know is there have any method change the ini.x.home_offset automaticaly after linuxcnc start?And how?

Aciera wrote:

Not sure if this is of any interest regarding 64bit values in LinuxCNC:
github.com/LinuxCNC/linuxcnc/pull/2034

I think this is not what I want.But thankyou anyway.

how is you C knowledge ?

I can give advice how to build a small component for encoder readout at startup in front of the cia402 comp.

unfortunaly i am currently on tour and will have no options the next weeks, to code and test this by myself.

I can wirte another state machine, but I think it is not necessary to do this for now. When I solve this problem I will post it. Thank you for all.

since I use the abs 17bit encoder. I write a simple comp for this. And the hal file is as bellow. Besides, The machine I use is hexapod.