I have an arduino nano running as an I2C slave. The master is an arduino uno connected to the slave using a short wire (ca. 10cm) icw a pullup resistor.
The slave is more or less just driving a stepper using the accelstepper lib. Stepper parameters and pseudo commands are send to the slave by the master. The master's main puprose is being the user interface and preparing commands/parameters to let the slave stick to it's job: driving the stepper.
Regarding to the communication between master/slave I created a union of a 32 byte array and a struct which contains all info which is shared between slave and master.
The byte array is used to transfer (partially) the buffer.
union I2Cbuf_u {
unsigned char byte[0];
struct {
struct {
uchar recType : 4;
uchar cmd : 4;
} xfer;
union {
sldrFlds_s sldrFlds; //REC_TYPE_SLDR_
dslrFlds_s dslrFlds; //REC_TYPE_DSLR_
expFlds_s expFlds; //REC_TYPE_EXPOSURE_
expTrackFlds_s expTrackFlds; //REC_TYPE_EXPOSURETRACK_
tmlapseFlds_s tmlapseFlds; //REC_TYPE_EXPOSURETMLAPSE_
} rec;
} content;
};
It's working all just fine but when the buffer is transferred while the stepper is still stepping it stops stepping for about 400-600ms. (just a quess..) At that time the only thing the slave is doing is stepper.run() in a loop.
I'm using the I2C Wire.h library and default clock speed. (both master and slave)
Any idea if this is a quite normal delay or should the I2C transfer of 32bytes be hardly noticable while the stepper is running. (or: there is probably something wrong in the setup\programming or this is about the performance I could expect..?)
Now the transfer is completely handle in the Wire.onReceive Wire.onRequest interrupts.
Maybe I can just set a flag and then handle the transfer in the loop() outside the interrupt. But if the transfer just takes so much time this wouldn't be much of a help probably.
