![]() Data should be logged to an SD-card found on a "Arduino Wireless SD shield". Again, your proposition is in line with what is happening at the hardware level.I have need for a data logging application running on a "Arduino compatible" chipKit UNO32 board, with a connected sensor. Interrupts have nothing to do with it - they are separate, and operate in parallel.Īs the Master has to wait at least for 64 us (assuming kbits/sec) for the data to arrive into SPDR of Master from the SPDR of the Slave (Fig-1), there may (very unlikely) appear interrupt which will be honored in parallel while the data from Slave to Master is still in transition. My reading of the datasheet is that when a byte is written to SPDR it gets sent, and the incoming byte is received. The data transfer time from MasterSlave at 125 kbits/sec rate is: (1/125000)*8 = 64 us. The instruction execution time is the time that the MCU needs to fetch the code (E205) from flash, put it into instruction register for decoding, and then placing to the control matrix (the sequence generator). It is also for the note of OP that the execution time of SPDR = 0x25 instruction is equal to the execution times of the above two assembly lines, which is : (1/16000000)*2 = 0.125 us (these are 1-cycle instructions). However, care must be taken into consideration that the interrupt interval is long enough (and practically, it is long enough) so that the MCU has time to execute the codes of the MLP (main line program). It is for the note of OP that there is no way for the SPI transaction to get out-of-order due to interrupt. The instruction: out SPDR, r16 which actually loads the data into SPDR register will be executed after returning from ISR. The SPDR = 0x25 instruction is further broken down into the following codes: ldi r16, 0x25 E205įrom the above break down of codes, we may state that the interrupt may arrive during the execution of this instruction: ldi r16, 0x25. Therefore, the interrupt process may proceed in parallel.įigure-1: SPI transaction between Master and Slaveīut, there is still something to say in the light of my working experience with interrupt processes of 8085, 6802, 80x86, 89S52, ATmega32A, and ATmega328P. I fully agree with you what you have said, and it is clearly demonstrated by the following SPI hardware structure where once data is loaded into SPDR register, the SCK is automatically generated by the dedicated hardware to complete simultaneous data exchange between Master and Slave without the intervention of MCU. I think (but have not checked the Atmega 328 datasheet (hint)) that the single byte SPI transfer is handled by hardware that is not affected by interrupts. ![]() (While the MCU returns to mainline program, the global interrupt flag is automatically activated.) There is no issue of pollution or loss of signal. It will the resume the mainline program from the point where it was interrupted. It will retrieve return address from stack ħ. It will then jump to ISRTOV0 (interrupt sub routine due to Timer-0 overflow).Ħ. It will deactivate global interrupt flag to prevent the occurrence of any other interrupt until the current interrupt process is finished Ĥ. It will then save the address of the next instruction (which the MCU would execute in absence of interrupt) onto stack ģ. The MCU will finish this (current) instruction Ģ. If interrupt arrives during the execution of SPDR = 0x25 code, the following events occur:ġ. The above Arduino SPI code is functionally equivalent to the following register level codes: SPDR = 0x25 Let us see what happens when an interrupt occurs due to TOV0 (Timer-0 overflow) flag while the MCU is executing the following Arduino SPI Code: byte x = SPI.transfer(0x25) Thanks in advance! This is my first post on this forum but I've found it to be an invaluable resource for quite a while. I suspect (and hope!) number 3 is the case, as in this application the interrupts are very time sensitive and I would prefer to not have anything get in their way-however it's been hard to find a concrete answer since most of my searches are polluted by people trying to perform SPI inside an interrupt. The Arduino simply stops clocking out data via SPI, essentially "pausing" it to handle the interrupt, and data transmission successfully resumes after a delay to handle the interrupt.Handling of the interrupt is ignored or delayed while the SPI library is transmitting data.The outbound data gets mangled due to an unexpected disruption of the transmission.My question is: What happens if one of my interrupts fires while my Nano is transmitting data via SPI? ![]() I have a project I'm working on that has two interrupts (one attached to timer0 and one triggered off of a pin) and a display driven by eight different subordinate boards via an SPI interface.
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