i2c error

[hongjo]

Dear ST 

I have some question about i2c read functions 

Currently we use zephyr os (version 3.4.0) 

the stm32f412RGT used as the host and the host  reads a 5-byte value from another mcu used as a slave through

i2c

the following problem occurs once every 3 hours after that i2c gets stuck.

uint8_t rx_buf[5];

rc = i2c_read_dt(&cfg->bus, rx_buf, sizeof(rx_buf));

When the host reads the last byte 0x3f normally, it should send nack instead of ack to slave , but it seems that i2c is stuck because ack is sent to slave . Is there a way to solve this?

thanks

BR

MR.SHIM 

[Andrew Neil]

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@hongjo wrote:

the following problem occurs once every 3 hours  

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Is that exactly 3 hours, or just "some time around 3 hours" ?

Repeatable?

Schematic & details of the slave may help.

[hongjo]

Dear guru

It takes about 3 hours, but when it happens quickly, the I2C STUCK happens in 30 minutes.

When I modified the code on the slave to process it as if it received a nack even though the host sent an ack at the end of the read, the i2c stuck did not occur even after several days of operation

thanks

BR

Mr.shim 

[bmckenney]

In the F4 series, having the master-receiver generate a NACK after the final byte requires byte-by-byte management of the CR1:ACK bit. The flow control model requires setting ACK=0 while the (N-1)th byte is complete, before accepting the (N-2)th byte from the RXDR. This is a bit of a dance, but is described in RM0402 Sec 4.3.3.  [I much prefer later versions of the I2C unit, which know what a transaction is.]

Once the master-receiver has ACK-ed the (final) byte, it has handed over SDA to the slave-transmitter, so (in general) the master can't issue a Stop (or anything else).

It appears that the Zephyr driver doesn't always get this sequence right. I regret to say that you probably have to take this up with the Zephyr people.