Dave;
I agree with your concern. Blocking interrupts may cause an unacceptable delay in the i2c response from the attiny85. It needs to be tested.
My little digispark module is set to run at 16.5 MHz. Maybe those four variable assignments can be completed in a microsecond or so, and the i2c bus will never know anything happened.
Some instructions:
I added the link?? ?
to the additional boards manager URLs in my version 1.8.19 Arduino IDE, downloaded the attinycore? version 1.5.2 by Spence Konde using the boards manager, set the board type to attiny85 (micronucleus / digispark) hit the upload tool in the Arduino IDE, then plugged in the digispark module when the IDE prompted me to do so. The program is only using 1278 bytes or 19% of the code space (6586 bytes total available before programming) and 11% of the variable space. There's plenty of room for growth. Program sizes above are for Farhan's original code. I haven't added the interrupt blocking code or made any other changes yet.
This is going in a slightly different direction than Farhan is suggesting in his notes at the top of the .ino program. Looks like he might be using totally blank attiny85's. I'm starting with a digispark module that has a bootloader already installed.
I haven't tested it yet, just programmed it. So my "instructions" might be a total waste of time to follow. At least all the stars aligned, all the libraries needed were present, the compile completed successfully, and the code downloaded into the module!
The digispark module is set up for +5 Volts. I'll have to see if it will be happy running at +3.3 Volts. I'm not sure which option is best -- I could wire it up to +5 Volts, but then there's the remote possibility that the I/O pins might output +5 Volts on the same bus where the RTC, SI5351, and Raspberry Pi are connected, which are all 3.3 Volt devices. The other option is to connect the module to +3.3 Volts which (assuming it runs) would eliminate the possibility of 5 Volts on the i2c bus, but it does add an additional load to the 3.3 Volt regulator at the SI5351. And we know how that regulator will fail if something makes it unhappy.
73; Steve, N3SB
