d9269112ee
AVR uses Hardward architecture with separate address space for program memory (flash) and data memory (RAM). Normal program flow can only access data memory which means that all variables - including const variables - have to be copied into RAM to be accessible. (This happens automatically during startup.) It is possible to work around this limitation in software but that can have severe impact on performance and/or API complexity. It is hardly feasible to change NuttX interfaces in a way that would allow to make use of this workaround. On newer AVR families, there is an alternative option enabled by this patch. These chips map part of their program memory (a 32kB window) into data memory address space. This patch leverages this feature and adds support for placing const variables into the mapped window. No copy to RAM is done for them. Const variables are therefore loaded directly from flash (not consuming RAM) while still being available to be used by any NuttX interface. Linker script of breadxavr board is changed to make use of these changes. Tested by verifying string addresses - parameters in printf call in a custom application (and also by running the application and verifying its output.) Documentation tested by build. Signed-off-by: Kerogit <kr.git@kerogit.eu>
85 lines
1.7 KiB
Text
85 lines
1.7 KiB
Text
#
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# For a description of the syntax of this configuration file,
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# see the file kconfig-language.txt in the NuttX tools repository.
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#
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if ARCH_AVR
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choice
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prompt "Atmel AVR chip selection"
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default ARCH_CHIP_AT32UC3
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config ARCH_CHIP_ATMEGA
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bool "ATMega family"
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select ARCH_FAMILY_AVR
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select MM_SMALL
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---help---
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Atmel ATMega family of 8-bit AVRs.
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config ARCH_CHIP_AT90USB
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bool "AT90USB family"
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select ARCH_FAMILY_AVR
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select MM_SMALL
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---help---
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Atmel AT90USB family of 8-bit AVRs.
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config ARCH_CHIP_AVRDX
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bool "AVR 32/64/128 DA/DB core"
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select ARCH_FAMILY_AVR
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select MM_SMALL
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select ARCH_HAVE_TICKLESS
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select AVR_HAVE_FLMAP
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---help---
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Atmel/Microchip AVR 32/64/128 DA/DB core family.
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config ARCH_CHIP_AT32UC3
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bool "AVR32 AT32UC3* family"
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select ARCH_FAMILY_AVR32
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---help---
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Atmel AT32UC3A/B/C family of 32-bit AVR32s.
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config ARCH_CHIP_AVR_CUSTOM
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bool "Custom AVR chip"
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select ARCH_CHIP_CUSTOM
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---help---
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Select this option if there is no directory for the chip under arch/avr/src/.
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endchoice
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config ARCH_FAMILY_AVR
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bool
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default n
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select ARCH_HAVE_STACKCHECK
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select ARCH_LDST_16BIT_NOT_ATOMIC
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config ARCH_FAMILY_AVR32
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bool
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default n
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config ARCH_FAMILY
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string
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default "avr" if ARCH_FAMILY_AVR
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default "avr32" if ARCH_FAMILY_AVR32
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config ARCH_CHIP
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string
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default "atmega" if ARCH_CHIP_ATMEGA
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default "avrdx" if ARCH_CHIP_AVRDX
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default "at90usb" if ARCH_CHIP_AT90USB
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default "at32uc3" if ARCH_CHIP_AT32UC3
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source "arch/avr/src/common/Kconfig"
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if ARCH_FAMILY_AVR
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source "arch/avr/src/avr/Kconfig"
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source "arch/avr/src/at90usb/Kconfig"
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source "arch/avr/src/atmega/Kconfig"
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source "arch/avr/src/avrdx/Kconfig"
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endif
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if ARCH_FAMILY_AVR32
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source "arch/avr/src/avr32/Kconfig"
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source "arch/avr/src/at32uc3/Kconfig"
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endif
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endif # ARCH_AVR
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