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Which kind of flash do you use? I recently phased in some extensions. I tested with standard Winbond & Gigadevice flashes. Can you send me the spi_flash_programmer_client.py status-register spi_flash_programmer_client.py id-register...

Well, from the description it's not 100% sure what fails here. The Arduino implementation polls the status register after every "page program". The loop in impl_wait_for_write_enable() has no end condition...

I am open for a discussion.

Yes, readPage/writePage and the binary implementations contain lots of duplicate code. I will rework that. Thanks for the note with 'Diecimila' I wasn't aware of that. Let me dig into...

It looks like the first wait may be required to keep compatibility with older boards. According to https://pyserial.readthedocs.io/en/latest/pyserial_api.html#serial.Serial.open there might be a short glitch on DTR when opening the port....