MSP430FR2676: I2C Slave Read with Delay

Eric Smith

Hello,

I am trying to set up the MSP430FR2676 as an I2C slave to communicate with a host MPU. I have been able to get the I2C slave to work successfully for both reading and writing basic data. I also have an I2C master set up on the MSP430 that communicates with a few external sensors and drivers that has been working well. I am now trying to do an I2C slave read that is a little more complicated because it requires a delay as part of the read. Below is a step-by-step description of what I need to do:

MPU sends I2C slave read command to MSP430 in order to read value from a sensor
MSP430 enters I2C slave interrupt to process the call from MPU
MSP430 sends an I2C write command to the sensor in order to initiate a measurement
MSP430 I2C slave process must wait for 1 second in order for sensor measurement to complete (This is where I am struggling)
MSP430 sends an I2C read command to the sensor to retrieve measurement results
MSP430 sends measurement data back to MPU

What I am struggling with is how to run a delay in the I2C slave process while allowing the other processes in the MSP430 to run. I know of the __delay_cycles command, but I know that causes the MSP430 to stop running all other processes. Is there a way to do the delay while still allowing other processes to run?

Thanks!

over 3 years ago

0 Keith Barkley over 3 years ago

Guru 43965 points

I am confused by what you mean by "processes" Are you using an RTOS? (If so, which one) or just the interrupt handlers?

https://e2e.ti.com/support/microcontrollers/msp-low-power-microcontrollers-group/msp430/f/msp-low-power-microcontroller-forum/303024/how-__delay_cycles-works

A timer is the more processor friendly approach.

0 Eric Smith over 3 years ago in reply to Keith Barkley

Prodigy 240 points

Hi Keith,

I am primarily using the MSP430FR2676 to run the CapTIvate process to measure capacitive touch sensors. I don't want those sensors to stop running for 1 second while the sensor is being read.

0 David Schultz over 3 years ago

Guru 26345 points

Using the various available interrupts for the I2C hardware is a much better way to deal with a target that takes a long time like this. Actually, the best way is for the target to have an output that can be tied to a GPIO to signal when data is ready.

Which is how the MSP430 should handle the MPU read rather than (apparently) leaving an I2C transaction hanging.

0 Eric Smith over 3 years ago in reply to David Schultz

Prodigy 240 points

Hi David,

I do have a GPIO connected to our MPU to indicate to it that a capacitive touch event has occurred on the MSP430. I could use that same GPIO to indicate to the MPU that the data is ready. That seems to me to be the best option. I will go ahead and do that.

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MSP430FR2676: I2C Slave Read with Delay