Adding subsection on Full_Access_Only aspect #1170
Conversation
Parts of the code examples are inspired by the Ada Drivers Library (https://github.com/AdaCore Ada_Drivers_Library).
We need the `-gnat2022` switch to run this example.
| :ref:`volatile type <Adv_Ada_Shared_Variable_Control_Volatile>` or an | ||
| :ref:`atomic type <Adv_Ada_Shared_Variable_Control_Atomic>`. (In other words, | ||
| if a type is neither volatile nor atomic, it cannot be a full access type.) | ||
|
|
There was a problem hiding this comment.
Should there be a reminder that any atomic type is automatically also volatile?
|
|
||
| As we already know, the value of a volatile object may be constantly changing, | ||
| so the compiler generates code in such a way that the process must read the | ||
| value of the volatile object from memory for each access. (In other words, the |
There was a problem hiding this comment.
Consider simplifying this:
"so the compiler generates code in such a way that the process must read the
value of the volatile object from memory for each access"
to be instead something like this:
"so the compiler generates code to read the
value of the volatile object from memory for each access"
| type, these assignments are performed for the complete 32-bit register, even | ||
| though we're updating just a single component of the record object. (Note that | ||
| if :ada:`Window_Register` wasn't a *full-access* object, an assignment such as | ||
| :ada:`WR.Horizontal_Cnt := 800` could be performed with a 16-bit operation.) |
There was a problem hiding this comment.
Regarding "could be performed with a 16-bit operation": This is in an admonition, but it is central to the concept because it is what the compiler would want to do otherwise, because that is more efficient than manipulating the entire object.
| end Show_Registers; | ||
|
|
||
| A delta assignment using an aggregate such as :ada:`(WR with delta ...)` | ||
| includes reading the value of complete 32-bit :ada:`WR` object from memory, |
There was a problem hiding this comment.
Should "value of complete" be "value of the complete"?
| atomic reads and updates, which |mdash| as a whole |mdash| are indivisible, | ||
| i.e. they must be done in a single instruction, so that no other instruction | ||
| could execute on that same object before the read or update completes. | ||
|
|
There was a problem hiding this comment.
Maybe a reminder that atomic implies volatile should go here (instead of above)?
|
|
||
| .. admonition:: For further reading... | ||
|
|
||
| By running on an PC, we can compare the |
There was a problem hiding this comment.
"on an PC" should be "on a PC"
Rework of #1146