Re: [M16C] : 20 bit data access

["Naveen H.S." <naveen dot hs at kpitcummins dot com>]

Hi DJ,

>> From the above, I think I like this plan:

Please ignore my earlier post on this topic. We have modified the
proposed solution to incorporate your suggestions. We would be glad if
you could verify it again.

By default all the constant variables will be stored in the far memory
('.frodata' section) and will be accessed using "LDE" instruction. The
non-initialized non-constant variables will be stored in near memory
('.nbss' section) and will be accessed using "MOV" instructions. The
initialized non-constant variables will be stored in near memory
('.ndata' section) and will be accessed using "MOV" instructions.

* By default, all the constant variables will be placed in the far
memory. They will be accessed using LDE instructions ('.frodata'
section)). 
* New attribute "near" will be added. This attribute will be used for
the latest M16C targets that have 4K/8K flash in near Memory.
* Constant variables specified with the attribute "near" will be placed
in a section ".nrodata" (near memory) and will be accessed using "MOV"
instruction.
* By default, non-constant initialized variables will be placed in near
memory.
* By default, non-constant non-initialized variables will be placed in
near memory.
* New attribute "far" (to use external memory for non-constant data
storage) will be added. 
* Non-constant non-initialized variables specified with the attribute
"far" will be placed in a section ".fbss" (far memory). 
* Non-constant initialized variables specified with the attribute "far"
will be placed in a section ".fdata" (far memory).
* LDE/STE instructions will be used to access the non-constant variables
specified with the attribute "far".
* MOV instructions will be used to access the constant variables
specified with the attribute "near".
* Default linker script will be modified for placing the default section
'.nbss', '.ndata' and '.nrodata' in near memory and '.fbss', '.fdata'
and '.frodata' in far Memory.
* Separate libraries will be used for R8C and M16C targets. 
* As the libraries will be built without any attribute, all the constant
data in library will be accessed using LDE instructions. Similarly,
non-constant non-initialised and non-constant initialised data in
library will be accessed using MOV instructions.

Please comment on the above proposed solution.

Regards,
Naveen.H.S.
KPIT Cummins Infosystems Ltd,
Pune (INDIA) 

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