Thank You! I pointed previously Gyurco's attention to this project, as soon as the source code will be available, he will investigate the option of porting. He migrated the SNES and Sega Genesis/Megadrive cores formerly, so I doubt that EP core could cause serious problems...

Probably Bruce or Zozo can help, they know how EXOS loads from tape.

I checked the Dave addons by IstvánV.
A7h port
    b0-b2: sync on (high means)
        the counter of belonging channel is not running
        the counter is hold continuously on frequency values are set in A0h-A5h registers
        flip-flip of tone generator output is set to 0
    b5-b6: the interrupt is driven by the counter of belonging tone generator (not the modified (filtered, distorted)), after each run to 0 bit0 of B4h port change, and (if interrupt is enabled) bit1 is set.
1KHz interrupt is equal to 250-1 tone generator frequency, and 50Hz is equal to 5000-1, so it differs from the video interrupt, it 80000 Z80 T-State (or 120000 if bit1 of port BFh is set)

I saw that all Dave interrupt is set during loading, but i think only Dave programmable interrupt is used during reading tape signal, and sync bit set/reset, and when 4 KB chunk is loaded then it changes to 50Hz Dave interrupt, and when tape read starts again it is on 1000Hz dave interrupt, but after some instructions it changes to programmable interrupt with tone0 sync high and wait until signal starts, if it is started then it release sync bit, and reset Dave interrupt (ld a,03h  , out (0b4h),a  )

Thank you again

Then...

If sync is 1 the counter of belonging channel is not running? Also in the middle of the count? Or only at the end?
Flip-flip of tone generator output is set to 0 at the end of the count?

I have to read the last paragraph carefully

As i understand, when sync bit set, it stops immediately the counter of the channel, and the counter is hold ony frequency value which is set by it's belonging tone registers (a0h-a5h)