Re: implementation of Bounded_String

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 18-01-19 14:57 , Dmitry A. Kazakov wrote:
> On 19/01/2018 12:54, Mehdi Saada wrote:
>
> [Trying to make sense from kind of meaningless questions]
>
>> I just wonder what's the lowest level (besides assembly) at which in
>> Ada, one can implement characters input-output.
>
> You cannot do I/O in assembly in any way different to a higher level
> language. With an OS in place all I/O is queuing a request to some
> device driver.
>
>> But since Text_io is language-defined, I suppose there's nothing
>> closer to the hardware ?
>
> Among Ada standard means stream and direct I/O are the closest to the
> hardware in the sense that they add least to the data being read and
> written. [However that can depend on the OS which can translate streams
> and blocks into something else below]
>
> Calls to the native OS I/O facilities follow. There is nothing closer
> unless you are in the system kernel.

Or running "bare machine", without an OS, and with direct access to the 
I/O HW -- which means that you are, in some sense, part of the "system 
kernel", such as it is.

In a bare machine environment, Text_IO.Put (Item : in Character) is 
often implemented like this (in Ada, usually):

    while UART_Tx_Register.Busy loop null; end loop;

    UART_Tx_Register.Data := Item;

where UART_Tx_Register is mapped to the transmission register of the 
UART peripheral.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
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