i2c arbitration during communication -few problems

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yuvalkesi

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Hi,
Well actually, it is happening, and I'm quite confused....
I'm working on a PCI-E system with 2 masters on an SMBUS protocol (COMEX CPU connected to an FPGA board). One is the FPGA (=me), the other is the CPU.
I see in the signal tap that during my transmission, and there is NO stop condition what-so-ever, suddenly the other master (CPU) pulls up the SDA line and takes charge, meaning I lost arbitration.
How can it happen?
I had no stop condition!
I'm also seeing that the line was not released after that, i.e., the sda line is low after while, and it stays like this forever, practically braking my state machines.
Interesting to say, it does not happening with other COMEX of different brands.

Any help will do!
Thx.
 

suddenly the other master (CPU) pulls up the SDA line and takes charge, meaning I lost arbitration.
Pulling up can hardly happen on the open drain I2C bus...
 

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