arch: added support for the riscv32 architecture
RISC-V is an open-source instruction set architecture.
Added support for the 32bit version of RISC-V to Zephyr.
1) exceptions/interrupts/faults are handled at the architecture
level via the __irq_wrapper handler. Context saving/restoring
of registers can be handled at both architecture and SOC levels.
If SOC-specific registers need to be saved, SOC level needs to
provide __soc_save_context and __soc_restore_context functions
that shall be accounted by the architecture level, when
corresponding config variable RISCV_SOC_CONTEXT_SAVE is set.
2) As RISC-V architecture does not provide a clear ISA specification
about interrupt handling, each RISC-V SOC handles it in its own
way. Hence, at the architecture level, the __irq_wrapper handler
expects the following functions to be provided by the SOC level:
__soc_is_irq: to check if the exception is the result of an
interrupt or not.
__soc_handle_irq: handle pending IRQ at SOC level (ex: clear
pending IRQ in SOC-specific IRQ register)
3) Thread/task scheduling, as well as IRQ offloading are handled via
the RISC-V system call ("ecall"), which is also handled via the
__irq_wrapper handler. The _Swap asm function just calls "ecall"
to generate an exception.
4) As there is no conventional way of handling CPU power save in
RISC-V, the default nano_cpu_idle and nano_cpu_atomic_idle
functions just unlock interrupts and return to the caller, without
issuing any CPU power saving instruction. Nonetheless, to allow
SOC-level to implement proper CPU power save, nano_cpu_idle and
nano_cpu_atomic_idle functions are defined as __weak
at the architecture level.
Change-Id: I980a161d0009f3f404ad22b226a6229fbb492389
Signed-off-by: Jean-Paul Etienne <fractalclone@gmail.com>
2017-01-11 07:24:30 +08:00
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-include $(srctree)/arch/$(ARCH)/soc/$(SOC_PATH)/Makefile
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# Put functions and data in their own binary sections so that ld can
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# garbage collect them
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arch_cflags += $(call cc-option,-ffunction-sections) \
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$(call cc-option,-fdata-sections)
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KBUILD_AFLAGS += $(arch_cflags)
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KBUILD_CFLAGS += $(arch_cflags)
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KBUILD_CXXFLAGS += $(arch_cflags)
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soc-cxxflags ?= $(soc-cflags)
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soc-aflags ?= $(soc-cflags)
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KBUILD_CFLAGS += $(soc-cflags)
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KBUILD_CXXFLAGS += $(soc-cxxflags)
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KBUILD_AFLAGS += $(soc-aflags)
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2017-02-01 09:25:26 +08:00
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soc_ld_include := -I$(srctree)/arch/$(ARCH)/soc/$(SOC_PATH)/
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EXTRA_LINKER_CMD_OPT += $(soc_ld_include)
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