hholst
Topic Author
Posts: 3
Joined: 12 Sep 2019, 10:33

DI input reaction time

12 Sep 2019, 11:04

Hi All
As I understand the DI/DO modules is using the RS485 bus to communicate the RPi board.
How fast reaction time can I expect from an input is changed to the software is notified.
I have plans to write the program in C++, and how do I subscribe to the DI changes so I don't have to poll?
 
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dirk
KUNBUS
Posts: 491
Joined: 15 Dec 2016, 13:19

Re: DI input reaction time

12 Sep 2019, 17:14

Hi hholst, the reaction time depends on the amount of modules and the configuration. you may read the value out by
piTest -r RevPiIOCycle
. This value is the amount of ms without rounding up or down. So 2 may also mean 2.9 ms which leads to about 6 ms worst case. Currently there is no other option than polling.
 
hholst
Topic Author
Posts: 3
Joined: 12 Sep 2019, 10:33

Re: DI input reaction time

16 Sep 2019, 12:15

For the local GPIO pin's at the RPI board it is possible to get a notification using the IOctrl I can see in the WiringPI project.
So it is really a shame you have not from the beginning designed the inputs to be able to give an interrupt signal.
I can see the MAX31913 you use in the DI module does not either support an interrupt pin, but you could have implemented in the STM32F205 software a polling routine which could notify the RPI module via a RPI GPIO pin
I am looking for a maximum guarantied reaction time of 1ms
 
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dirk
KUNBUS
Posts: 491
Joined: 15 Dec 2016, 13:19

Re: DI input reaction time

18 Sep 2019, 13:40

Dear hholst, well thank you for your words. If you have a requirement of 1ms reaction time then the RevPi is unfortunately not fast enough today.

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