STM32F723 I2C bootloader : No-Stretch Erase command leads to long clock stretching anyway. How to deal with it?

[YSion.1]

Several questions:

• The I2C bootloader answers version 1.2 which is not documented in AN4221 even though it was recently updated in June 2021. Is it planned to publish this information soon?
• I am sending a "No-stretch Erase" command via the following operations:
  • I2C write to 0x4D : 0x45 ACK 0xBA ACK.
  • I2C Read to 0x4D : 0x79 nACK.
  • I2C Write to 0x4D : 0xFF ACK 0xFF ACK 0x00 ACK.
  • Then I try to issue a Read to 0x4D (to get the ACK/nACK/BUSY status) and the STM32 does clock stretching (holding clk down) at the ACK/nACK bit for 7 very long seconds. Is it normal that during the process of a "No Stretch" command, I get a clock stretch? How is the erase supposed to work?
• Since polling by issuing I2C Reads seems to fail, then I tried to add a sleep(10) (10 seconds) before issuing the I2C read for the ACK/nACK/BUSY. On the I2C lines I can see indeed a big 10 seconds gap after the 0xFF ACK 0xFF ACK 0x00 ACK. During the GAP bus is idle (SCL == 1, SDA == 1). Then when I issue the Read 0x4D, the read itself is nACKed, as if the I2C device 0x4D (the bootloader) was gone.
• I also tried with a smaller sleep(1) (1 second), it gives the same result as when there is no sleep at all. Meaning that upon issuing the Read to get the ACK/nACK/BUSY msg, when it comes to the ACK bit of the I2C frame the clock gets stretched for 6 seconds.

You can find details on this issue I am having, including I2C wave dump screenshots on the following thread: https://sourceforge.net/p/stm32flash/tickets/131/

Thank you for your help.

Best regards,

Yann

[dscdsc]

Running into this exact issue as well, wanted to bump this.

[dscdsc]

I was running into an issue when the bootloader restarted the STM32 (can be seen by looking at the NRST line) if the sleep() before checking the result of the erase command was too long. Asking for ACK after that naturally returned NACK. I was able to experimentally figure out that a single page erase takes 2s max and a full erase of STM32H750 is 5s. I'm now able to erase and flash.