twi: why use non-blocking functions?

[benwaffle]

For example, in i2c_master_write, you call HAL_I2C_Master_Transmit_IT() and then busy wait until HAL_I2C_GetState() == HAL_I2C_STATE_READY. Why not just use HAL_I2C_Master_Transmit(), the blocking function?

[fpistm]

IIRW, this was introduce to not block. Is it right @VVESTM ?
2e9dc4d

[VVESTM]

Yes, we introduce this in order to be able to use I2C and SPI in the same time. With the blocking functions, there was too much delay in the SPI.

[fpistm]

Any update on this?

[benwaffle]

Why would this make a difference? As long as the interrupt priorities are right, the SPI interrupts can occur while I2C is running. Do we know where the delays came from?

[uzi18]

maybe we need just add setNonblocking(true)

[VVESTM]

Trying to get back on this subject... This code has been introduced by #115 .
I made a mistake on my previous comment. The delay was introduced in I2C instead of SPI...

The use case was the following :
* on L475 IoT board, sensors are connected on I2C and BTLE on SPI (there is an IT on BTLE Rx)
* transfer on going on I2C, in polling mode.
* data available on BTLE, and so, an SPI transfer is launched on BTLE IT context.
* I2C transfer is blocked waiting for SPI ends.
=> this was making an error on I2C and we reach a timeout.

By replacing the polling mode by IT mode on I2C transfer, we can be interrupted by SPI.

[fpistm]

@benwaffle is @VVESTM answer your question?
Thanks in advance

[benwaffle]

How is the timeout check different? Whether in polling or interrupt mode, it calls HAL_GetTick() to get the current time, and that interrupt fires in every case (even if SPI or I2C is running). So why would it timeout in one case and not in another?

[fpistm]

Well, in the original case, I2C was not in IT mode.
Then when the BTLE request a RX thanks an EXTI, the callback was called immediately. If this happen during the HAL_I2C_Master_Transmit(), then this cause I2C transfer to fail.
Moving to HAL_I2C_Master_Transmit_IT() allowed to not break the I2C transfer as I2C has higher prio than the EXTI. That's all.

[fpistm]

Considered answered.