cederom commented on code in PR #16687:
URL: https://github.com/apache/nuttx/pull/16687#discussion_r2193596420
##########
arch/avr/src/avr/Kconfig:
##########
@@ -94,8 +110,76 @@ config AVR_HAS_MEMX_PTR
pointers in arbitrary interaction with the kernel. Not all API
functions have these qualifiers added to their parameters.
+config AVR_HAS_FLMAP
+ bool "Use memory-mapped access to flash"
+ depends on AVR_BOARD_HAS_FLMAP && AVR_CHIP_HAS_FLMAP
+ ---help---
+ Newer AVR chips - namely tinyAVR and AVR families - have (part
of)
+ their program memory (flash) mapped into data memory address
space.
+ The mapping is limited to 32kB window.
+
+ With this option enabled, const variables are kept in the
program
+ memory and no copy to RAM is done. Yet it is still possible to
use
+ such variables in any interaction with the kernel as they are
+ visible in data memory address space.
+
+ Note that this option only triggers some basic configuration
+ in the init function. It is the linker script of the board that
needs
+ to ensure variables are placed correctly.
+
+ Beware that FLMAP bits in NVMCTRL.CTRLB I/O register which
select
+ the segment of program memory to be mapped may not be changed
freely
+ by the application. If the application needs to change the
mapping,
+ it may only do so while observing these rules:
+
+ 1. No kernel function must be called until the original value
+ is restored.
+
+ 2. Interrupts must be disabled for as long as the value is
changed.
+
+endchoice # Const variable placement
+
+config AVR_FLMAP_RODATA_SIZE
+ int "Size of .rodata FLMAP section"
+ depends on AVR_HAS_FLMAP
+ default 4096
+ ---help---
+ Specify size of .rodata memory section, ie. the section that
stores
+ const variables. This will be passed as a parameter to the
linker
+ to be used by the board's linker script.
+
+ Value must be divisible by 512 and no more than 32 kilobytes
+ is possible.
+
+config AVR_FLMAP_RODATA_OFFSET
+ int "Offset of .rodata FLMAP section"
+ depends on AVR_HAS_FLMAP
+ default 0
+ ---help---
+ Specify size of memory block between end of the .rodata section
+ (counting its full size as defined in AVR_FLMAP_RODATA_SIZE)
+ and the end of flash.
+
+ This value is intended to leave the end of the flash unused,
+ presumably for the purpose of placing APPDATA section in there
+ (see the chip documentation for details about subdividing
+ the program flash to BOOT, APPCODE and APPDATA sections.)
+
+ Note that this value is only passed to the linker to be used
+ by the linker script - the script then needs to place
+ the .rodata section accordingly.
+
+ Value must be divisible by 512 and no more than 31 kilobytes
+ is possible. Sum of this value and AVR_FLMAP_RODATA_SIZE must
+ also not exceed 32kB.
config AVR_HAS_RAMPZ
bool
+config AVR_BOARD_HAS_FLMAP
+ bool
+
+config AVR_CHIP_HAS_FLMAP
Review Comment:
`ARCH_HAVE_AVR_FLMAP` ? existing `ARCH_HAVE_` prefix aligns with existing
nomenclature and allows easy filtering / sorting? :-)
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