noob question 1

[stevech]

New user w/apologies...
In ZBasic, if one reads or writes a RAM variable that is larger than one byte, say, using Register.RTCtick, or any such that is altered by an interrupt routine, how does one code to protect the volatility? I would normally do CLI and SEI while reading or writing that variable, if an ISR might change its value. Perhaps Register.RTCtick takes care of this. But what about other cases?

[mikep]

This is a good question and would be a concern if you were using the AVR directly but you are not. The answer to the question is that you don't need to worry about such things as the Virtual Machine inside the ATmega32 (the ZBasic runtime) takes care of this for you. ZVM is an acronym for ZBasic Virtual Machine

The longer answer involves explaining why this is the case. The ZBasic compiler converts your Basic program into an intermediate language (the ZXB file) that is then downloaded to the SPI EEPROM. The ZBasic runtime loads this program and interprets each instruction and executes it. The instructions can be seen if you generate a list file from the compiler. Each instruction (e.g. push long onto stack) executes as a single unit before the next instruction in the same or different task is executed. While executing the instruction it is possible to receive an interrupt. This is serviced by the ZBasic runtime which may set or clear interrupts (the SEI/CLI) and then completes execution of the virtual machine instruction.

On my website (see below) I have an article that explain the ZBasic architecture (the ZBasic intro one). There is also a series of 6 articles that explains the BasicX internal architecture and virtual machine. ZBasic is similar is many ways but the virtual machine instructions are different.

[dkinzer]

The ZBasic Virtual Machine firmware takes care of that for you as long as you access the data item by the "normal means". By this I mean using a value in an expression or assigning to a (register) variable. On the other hand, if you were to read the value of Register.RTCTick by using BlockMove(), the transfer is not guaranteed to be atomic and may produce incorrect results.

There is no mechanism for disabling interrupts in user code.

[stevech]

thanks. Got it.