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I personally think that its 'representation clauses' are a really awesome feature for bare-metal programming. It's a shame other languages haven't borrowed this

by ajxs 3y ago

I personally think that its 'representation clauses' are a really awesome feature for bare-metal programming. It's a shame other languages haven't borrowed this idea.

thesuperbigfrog 3y ago
Representation clauses are by far the biggest feature for embedded programming: https://learn.adacore.com/courses/advanced-ada/parts/data_types/types_representation.html https://learn.adacore.com/courses/advanced-ada/parts/data_ty... http://www.ada-auth.org/standards/22rm/html/RM-13-1.html http://www.ada-auth.org/standards/22rm/html/RM-13-1.html Wouldn't it be nice in C to be able to define how a struct is laid out in the machine representation? In Ada, you can and it is part of the standard, so it is portable: https://learn.adacore.com/courses/advanced-ada/parts/data_types/types_representation.html#record-representation-and-storage-clauses https://learn.adacore.com/courses/advanced-ada/parts/data_ty...
- Galanwe 3y ago
  It's difficult for someone with 0 knowledge of the language to really understand representation clauses. It does seem to be similar to enum values in C++? // Ada for Day use (Mon => 2#00000001#, Tue => 2#00000010#, Wed => 2#00000100#, Thu => 2#00001000#, Fri => 2#00010000#, Sat => 2#00100000#, Sun => 2#01000000#); // C++ enum Day { Mon = 0b00000001, Tue = 0b00000010, Wed = 0b00000100, Thu = 0b00001000, Fri = 0b00010000, Sat = 0b00100000, Sun = 0b01000000, }; As for the record representation, my understanding is that it is equivalent to having a normalized __attribute__((__packed__)), where smart compiler padding is disabled and you can arbitrarily decide the memory layout of your struct?
  - deleted 3y ago
    [deleted]
  - glacia01 3y ago
    Representation clause is just language defined way of how struct (Record in Ada) Enum or Array are actually laid out in memory. So, for example, you can define a struct that represents a register, overlay that register address and use it like this: procedure Enable_USB_Clock is begin Registers.PMC_Periph.PMC_SCER.USBCLK := 1; end Enable_USB_Clock; Example taken from here: https://learn.adacore.com/courses/Ada_For_The_Embedded_C_Developer/chapters/04_Embedded.html#register-overlays https://learn.adacore.com/courses/Ada_For_The_Embedded_C_Dev...

by ajxs 3y ago

I personally think that its 'representation clauses' are a really awesome feature for bare-metal programming. It's a shame other languages haven't borrowed this idea.

thesuperbigfrog 3y ago

Representation clauses are by far the biggest feature for embedded programming: https://learn.adacore.com/courses/advanced-ada/parts/data_types/types_representation.html https://learn.adacore.com/courses/advanced-ada/parts/data_ty... http://www.ada-auth.org/standards/22rm/html/RM-13-1.html http://www.ada-auth.org/standards/22rm/html/RM-13-1.html Wouldn't it be nice in C to be able to define how a struct is laid out in the machine representation? In Ada, you can and it is part of the standard, so it is portable: https://learn.adacore.com/courses/advanced-ada/parts/data_types/types_representation.html#record-representation-and-storage-clauses https://learn.adacore.com/courses/advanced-ada/parts/data_ty...

Galanwe 3y ago
It's difficult for someone with 0 knowledge of the language to really understand representation clauses. It does seem to be similar to enum values in C++? // Ada for Day use (Mon => 2#00000001#, Tue => 2#00000010#, Wed => 2#00000100#, Thu => 2#00001000#, Fri => 2#00010000#, Sat => 2#00100000#, Sun => 2#01000000#); // C++ enum Day { Mon = 0b00000001, Tue = 0b00000010, Wed = 0b00000100, Thu = 0b00001000, Fri = 0b00010000, Sat = 0b00100000, Sun = 0b01000000, }; As for the record representation, my understanding is that it is equivalent to having a normalized __attribute__((__packed__)), where smart compiler padding is disabled and you can arbitrarily decide the memory layout of your struct?
- deleted 3y ago
  [deleted]
- glacia01 3y ago
  Representation clause is just language defined way of how struct (Record in Ada) Enum or Array are actually laid out in memory. So, for example, you can define a struct that represents a register, overlay that register address and use it like this: procedure Enable_USB_Clock is begin Registers.PMC_Periph.PMC_SCER.USBCLK := 1; end Enable_USB_Clock; Example taken from here: https://learn.adacore.com/courses/Ada_For_The_Embedded_C_Developer/chapters/04_Embedded.html#register-overlays https://learn.adacore.com/courses/Ada_For_The_Embedded_C_Dev...