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RISC-V: Implement simple and native NuttX SBI

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This is a minimalistic SBI implementation for NuttX.

Provides a single service for now:
- Access to machine timer

Provides a start trampoline to start NuttX in S-mode:
- Exceptions / faults are delegated to S-mode.
- External interrupts are delegated to S-mode.

Machine mode timer is used as follows:
- The timer compare match register reload happens in M-mode, via
  call gate "riscv_sbi_set_timer"
- The compare match event is dispatched to S-mode ISR, which will
  notify the kernel to advance time
- Clearing the STIP interrupt does not work from S-mode,
  so the call gate does this from M-mode

The only supported (tested) target for now is MPFS.
This commit is contained in:
Ville Juven 2022-04-11 13:46:41 +03:00 committed by Xiang Xiao
parent 76e5204a80
commit ae64f28344
14 changed files with 1099 additions and 0 deletions
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4
arch/risc-v/Kconfig
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@ -282,6 +282,9 @@ config RISCV_MISALIGNED_HANDLER
# Kernel mode requires this as M-mode uses flat addressing and the kernel
# memory must be mapped in order to share memory between the kernel and
# different user tasks which reside in virtual memory.
#
# Note that S-mode requires a companion software (SBI)
#
config ARCH_USE_S_MODE
bool "Run the NuttX kernel in S-mode"
@ -378,6 +381,7 @@ endchoice
endif
source "arch/risc-v/src/opensbi/Kconfig"
source "arch/risc-v/src/nuttsbi/Kconfig"
if ARCH_CHIP_FE310
source "arch/risc-v/src/fe310/Kconfig"

2
arch/risc-v/src/Makefile
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@ -22,6 +22,8 @@ include $(TOPDIR)/Make.defs
include chip/Make.defs
ifeq ($(CONFIG_OPENSBI),y)
include opensbi/Make.defs
else ifeq ($(CONFIG_NUTTSBI),y)
include nuttsbi/Make.defs
endif
# Kernel runs in supervisor mode or machine mode ?

30
arch/risc-v/src/nuttsbi/Kconfig Normal file
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@ -0,0 +1,30 @@
# S-mode requires a Supervisor Binary Interface (SBI) in order to access
# M-mode ISA. A minimalistic SBI is provided here natively.
config NUTTSBI
bool "Use NuttX native SBI"
default n
depends on ARCH_RISCV && ARCH_USE_S_MODE
---help---
Use NuttX minimalistic SBI
if NUTTSBI
config NUTTSBI_HART_CNT
int "Amount of harts in SoC"
default 1
config NUTTSBI_MTIME_BASE
hex "MTIME base address"
default 0
---help---
Sets the address of mtime memory mapped register
config NUTTSBI_MTIMECMP_BASE
hex "MTIMECMP base address"
default 0
---help---
Sets the address of mtimecmp memory mapped register
endif

33
arch/risc-v/src/nuttsbi/Make.defs Normal file
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@ -0,0 +1,33 @@
############################################################################
# arch/risc-v/src/nuttsbi/Make.defs
#
# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements. See the NOTICE file distributed with
# this work for additional information regarding copyright ownership. The
# ASF licenses this file to you under the Apache License, Version 2.0 (the
# "License"); you may not use this file except in compliance with the
# License. You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
#
############################################################################
# If NuttX SBI is needed
ifeq ($(CONFIG_NUTTSBI),y)
SBI_ASRCS += sbi_mtrap.S sbi_vectors.S sbi_head.S
SBI_CSRCS += sbi_mscratch.c sbi_mcall.c sbi_start.c
SBI_CSRCS += sbi_mexception.c sbi_mtimer.c
INCLUDES += ${shell $(INCDIR) "$(CC)" $(ARCH_SRCDIR)$(DELIM)nuttsbi}
SBI_DIR := nuttsbi
endif

131
arch/risc-v/src/nuttsbi/sbi_head.S Normal file
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@ -0,0 +1,131 @@
/****************************************************************************
* arch/risc-v/src/nuttsbi/sbi_head.S
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <nuttx/irq.h>
#include "sbi_internal.h"
/****************************************************************************
* Public Symbols
****************************************************************************/
/* Imported symbols */
.extern __mtrap_vec
.section .text
.global __start
__start:
/* Disable all interrupts (i.e. timer, external) in mie */
csrw mie, zero
csrw mip, zero
/* Initialize the Machine Trap Vector */
la t0, __mtrap_vec
csrw mtvec, t0
/* Make sure that mtvec is updated before continuing */
1:
csrr t1, mtvec
bne t0, t1, 1b
/* mscratch must be init to zero- we are not using scratch memory */
csrw mscratch, zero
csrw mcause, zero
csrw mepc, zero
li x1, 0
li x2, 0
li x3, 0
li x4, 0
li x5, 0
li x6, 0
li x7, 0
li x8, 0
li x9, 0
li x10, 0
li x11, 0
li x12, 0
li x13, 0
li x14, 0
li x15, 0
li x16, 0
li x17, 0
li x18, 0
li x19, 0
li x20, 0
li x21, 0
li x22, 0
li x23, 0
li x24, 0
li x25, 0
li x26, 0
li x27, 0
li x28, 0
li x29, 0
li x30, 0
li x31, 0
/* Delegation registers must be explicitly reset */
csrw mideleg, 0
csrw medeleg, 0
/* Remove MMU mappings (if any) */
csrw satp, zero
fence
/* Flush TLB (does not make a difference really) */
sfence.vma x0, x0
/* Clear PMP */
csrw pmpcfg0, 0
csrw pmpcfg2, 0
/* Set up a temporary stack */
#if MMODE_HART_CNT > 1
/* REVISIT: This requires that hartID is sequential, and starts from 0 */
csrr a0, mhartid
li s0, TEMP_STACK_SIZE
mul s0, a0, s0
la s1, TEMP_STACK_BASE
sub sp, s1, s0
#else
la sp, TEMP_STACK_BASE
#endif
/* Jump to start */
j sbi_start

144
arch/risc-v/src/nuttsbi/sbi_internal.h Normal file
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@ -0,0 +1,144 @@
/****************************************************************************
* arch/risc-v/src/nuttsbi/sbi_internal.h
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
#ifndef __ARCH_RISC_V_SRC_NUTTSBI_SBI_INTERNAL_H
#define __ARCH_RISC_V_SRC_NUTTSBI_SBI_INTERNAL_H
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#ifndef __ASSEMBLY__
# include <stdint.h>
#endif
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/* Amount of harts, based on chip capability, not utilization */
#define MMODE_HART_CNT (CONFIG_NUTTSBI_HART_CNT)
/* The machine mode interrupts should not be too complex */
#define MMODE_IRQSTACK (1024)
/* Timer interrupt is the only one we handle, others are discarded */
#define MTIMER_IRQ (7)
/* Timer memory mapped registers */
#define MTIMER_TIME_BASE (CONFIG_NUTTSBI_MTIME_BASE)
#define MTIMER_CMP_BASE (CONFIG_NUTTSBI_MTIMECMP_BASE)
/* For stack alignment */
#define STACK_ALIGNMENT 16
#define STACK_ALIGN_MASK (STACK_ALIGNMENT - 1)
#define STACK_ALIGN_DOWN(a) ((a) & ~STACK_ALIGN_MASK)
#define STACK_ALIGN_UP(a) (((a) + STACK_ALIGN_MASK) & ~STACK_ALIGN_MASK)
/* Temporary stack placement and size */
#define TEMP_STACK_BASE (_ebss)
#define TEMP_STACK (1024)
#define TEMP_STACK_SIZE (STACK_ALIGN_DOWN(TEMP_STACK))
/****************************************************************************
* Public Function Prototypes
****************************************************************************/
#ifndef __ASSEMBLY__
/****************************************************************************
* Name: riscv_mscratch_assign
*
* Description:
* Assign the mscratch register for hartid. Sets the M-mode interrupt stack
* which is a must because M-mode deals with flat addressing and cannot
* share the user stack for exception handling.
*
* Input Parameters:
* hartid - Hartid.
*
****************************************************************************/
void sbi_mscratch_assign(uintptr_t hartid);
/****************************************************************************
* Name: sbi_start
*
* Description:
* Sets up entry to board specific start routine in S-mode. Mandatory
* trampoline function when the native SBI is used. Called from M-mode.
*
****************************************************************************/
void sbi_start(void) noreturn_function;
/****************************************************************************
* Name: sbi_init_mtimer
*
* Description:
* Set up access to mtimer for SBI. This is an extremely light weight way
* of provisioning the mtimer memory mapped registers to SBI.
*
* Input Parameters:
* mtime - Pointer to machine time memory mapped register.
* mtimecmp - Pointer to the base of the mtimecmp memory mapped registers,
* implementation assumes there is 1 per hart and that they
* follow each other.
*
****************************************************************************/
void sbi_init_mtimer(uintptr_t mtime, uintptr_t mtimecmp);
/****************************************************************************
* Name: sbi_get_mtime
*
* Description:
* Read value of mtime
*
* Returned value:
* Full 64-bit system time
*
****************************************************************************/
uint64_t sbi_get_mtime(void);
/****************************************************************************
* Name: sbi_set_mtimecmp
*
* Description:
* Set value of mtimecmp.
*
* Input Parameters:
* value - Value for mtimecmp.
*
****************************************************************************/
void sbi_set_mtimecmp(uint64_t value);
#endif /* __ASSEMBLY__ */
#endif /* __ARCH_RISC_V_SRC_NUTTSBI_SBI_INTERNAL_H */

81
arch/risc-v/src/nuttsbi/sbi_mcall.c Normal file
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@ -0,0 +1,81 @@
/****************************************************************************
* arch/risc-v/src/nuttsbi/sbi_mcall.c
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <nuttx/irq.h>
#include <stdint.h>
#include "riscv_internal.h"
#include "sbi_mcall.h"
#include "sbi_internal.h"
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: sbi_mcall_handle
*
* Description:
* Handle environment call to machine mode
*
* Input Parameters:
* regs - User context
*
****************************************************************************/
void sbi_mcall_handle(uintptr_t *regs)
{
/* Check the environment call number */
switch (regs[REG_A0])
{
case MCALL_GET_TIMER:
#ifdef CONFIG_ARCH_RV64
regs[REG_A0] = sbi_get_mtime();
#else
{
uint64_t time = sbi_get_mtime();
regs[REG_A0] = (uint32_t)time;
regs[REG_A1] = (uint32_t)(time >> 32);
}
#endif
break;
case MCALL_SET_TIMER:
#ifdef CONFIG_ARCH_RV64
sbi_set_mtimecmp(regs[REG_A1]);
#else
sbi_set_mtimecmp(regs[REG_A1] + ((uint64_t)regs[REG_A2] << 32));
#endif
CLEAR_CSR(mip, MIP_STIP);
SET_CSR(mie, MIE_MTIE);
break;
default:
break;
}
}

134
arch/risc-v/src/nuttsbi/sbi_mcall.h Normal file
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@ -0,0 +1,134 @@
/****************************************************************************
* arch/risc-v/src/nuttsbi/sbi_mcall.h
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
#ifndef __ARCH_RISC_V_SRC_NUTTSBI_SBI_MCALL_H
#define __ARCH_RISC_V_SRC_NUTTSBI_SBI_MCALL_H
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <stdint.h>
/****************************************************************************
* Public Types
****************************************************************************/
enum mcall_num_e
{
MCALL_INVALID,
MCALL_GET_TIMER,
MCALL_SET_TIMER,
MCALL_LAST
};
/****************************************************************************
* Public Function Prototypes
****************************************************************************/
/****************************************************************************
* Name: mcall0
*
* Description:
* Generate an environment call to machine mode
*
* Input Parameters:
* nbr - Environment call number
*
****************************************************************************/
static inline uintptr_t mcall0(unsigned int nbr)
{
register long r0 asm("a0") = (long)(nbr);
asm volatile
(
"ecall"
:: "r"(r0)
: "memory"
);
asm volatile("nop" : "=r"(r0));
return r0;
}
/****************************************************************************
* Name: mcall1
*
* Description:
* Generate an environment call to machine mode
*
* Input Parameters:
* nbr - Environment call number
* parm1 - Argument for ecall
*
****************************************************************************/
static inline uintptr_t mcall1(unsigned int nbr, uintptr_t parm1)
{
register long r0 asm("a0") = (long)(nbr);
register long r1 asm("a1") = (long)(parm1);
asm volatile
(
"ecall"
:: "r"(r0), "r"(r1)
: "memory"
);
asm volatile("nop" : "=r"(r0));
return r0;
}
/****************************************************************************
* Name: sbi_mcall_get_time
*
* Description:
* Read the current system time (mtime)
*
* Returned Value:
* time - Value of mtime
*
****************************************************************************/
#define sbi_mcall_get_time() \
mcall0(MCALL_GET_TIMER)
/****************************************************************************
* Name: sbi_mcall_set_timer
*
* Description:
* Set new compare match value for timer. Time is in absolute time, so
* user must either obtain system time and calculate the offset, or keep
* the old compare match value in memory
*
* Input Parameters:
* stime_value - Absolute time for next compare match event
*
****************************************************************************/
#define sbi_mcall_set_timer(stime_value) \
(void)mcall1(MCALL_SET_TIMER, stime_value)
#endif /* __ARCH_RISC_V_SRC_NUTTSBI_SBI_MCALL_H */

37
arch/risc-v/src/nuttsbi/sbi_mexception.c Normal file
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@ -0,0 +1,37 @@
/****************************************************************************
* arch/risc-v/src/nuttsbi/sbi_mexception.c
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <stdint.h>
/****************************************************************************
* Public Functions
****************************************************************************/
void sbi_mexception(uintptr_t mcause, uintptr_t *mepc)
{
(void) mcause;
(void) mepc;
}

85
arch/risc-v/src/nuttsbi/sbi_mscratch.c Normal file
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@ -0,0 +1,85 @@
/****************************************************************************
* arch/risc-v/src/nuttsbi/sbi_mscratch.c
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <nuttx/irq.h>
#include <arch/barriers.h>
#include <stdint.h>
#include "riscv_internal.h"
#include "sbi_internal.h"
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
#define STACK_SIZE (STACK_ALIGN_DOWN(MMODE_IRQSTACK))
/****************************************************************************
* Public Data
****************************************************************************/
extern uintptr_t g_mintstacktop;
extern uintptr_t g_mintstackalloc;
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: sbi_mscratch_assign
*
* Description:
* Assign the mscratch register for hartid. Sets the M-mode interrupt stack
* which is a must because M-mode deals with flat addressing and cannot
* share the user stack for exception handling.
*
* Input Parameters:
* hartid - Hartid
*
****************************************************************************/
void sbi_mscratch_assign(uintptr_t hartid)
{
uintptr_t stack_top;
#if MMODE_HART_CNT > 1
/* Calculate offset first (stack size * hartid) */
/* REVISIT: This requires that hartID is sequential, and starts from 0 */
stack_top = (uintptr_t)&g_mintstacktop - hartid * STACK_SIZE;
#else
UNUSED(hartid);
stack_top = (uintptr_t)&g_mintstacktop;
#endif
WRITE_CSR(mscratch, stack_top);
/* Make sure mscratch is updated before continuing */
__DMB();
}

100
arch/risc-v/src/nuttsbi/sbi_mtimer.c Normal file
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@ -0,0 +1,100 @@
/****************************************************************************
* arch/risc-v/src/nuttsbi/sbi_mtimer.c
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <nuttx/compiler.h>
#include <nuttx/irq.h>
#include <arch/barriers.h>
#include <stdint.h>
#include "riscv_internal.h"
#include "sbi_internal.h"
#include "sbi_mcall.h"
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/****************************************************************************
* Private Data
****************************************************************************/
/* Memory mapped register base addresses */
static volatile uintptr_t g_mtimecmp locate_data(".noinit");
static volatile uintptr_t g_mtime locate_data(".noinit");
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Public Functions
****************************************************************************/
void sbi_init_mtimer(uintptr_t mtime, uintptr_t mtimecmp)
{
/* Set the memory mapped register bases */
g_mtimecmp = mtimecmp;
g_mtime = mtime;
}
uint64_t sbi_get_mtime(void)
{
#ifdef CONFIG_ARCH_RV64
return getreg64(g_mtime);
#else
uint32_t hi;
uint32_t lo;
do
{
hi = getreg32(g_mtime + 4);
lo = getreg32(g_mtime);
}
while (getreg32(g_mtime + 4) != hi);
return ((uint64_t)hi << 32) | lo;
#endif
}
void sbi_set_mtimecmp(uint64_t value)
{
uintptr_t mtimecmp = g_mtimecmp + READ_CSR(mhartid) * sizeof(uintptr_t);
#ifdef CONFIG_ARCH_RV64
putreg64(value, mtimecmp);
#else
putreg32(UINT32_MAX, mtimecmp + 4);
putreg32(value, mtimecmp);
putreg32(value >> 32, mtimecmp + 4);
#endif
/* Make sure it sticks */
__DMB();
}

154
arch/risc-v/src/nuttsbi/sbi_mtrap.S Normal file
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/****************************************************************************
* arch/risc-v/src/nuttsbi/sbi_machine_trap.S
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <nuttx/irq.h>
#include "riscv_macros.S"
#include "riscv_internal.h"
#include "sbi_internal.h"
/****************************************************************************
* Public Symbols
****************************************************************************/
/****************************************************************************
* Name: machine_trap
*
* Description:
* Machine mode trap handler. Handles Mtimer and simple mcall interface.
*
****************************************************************************/
.section .text
.global machine_trap
.align 8
machine_trap:
/* Switch to M-mode IRQ stack */
csrrw sp, mscratch, sp /* mscratch has user stack */
beqz sp, .Lmtrap /* Detect recursive traps */
addi sp, sp, -XCPTCONTEXT_SIZE
save_ctx sp
csrr a0, mcause /* exception cause */
csrrw s0, mscratch, x0 /* read user stack */
REGSTORE s0, REG_X2(sp) /* original SP */
/* Check if this is an exception */
bgez a0, .Lmexception
/* Figure out which interrupt this is */
sll a0, a0, 1 /* Shift msbit out */
li a1, MTIMER_IRQ * 2 /* Machine timer irq ? (shifted left) */
bne a0, a1, 1f
/* Delegate interrupt to S-mode handler */
li a0, MIP_MTIP
csrc mie, a0
li a0, MIP_STIP
csrs mip, a0
1:
/* Restore mscratch */
addi s0, sp, XCPTCONTEXT_SIZE
csrw mscratch, s0 /* original mscratch */
/* Restore original context */
load_ctx sp
REGLOAD sp, REG_SP(sp) /* restore original sp */
/* Return from Machine Interrupt */
mret
.Lmexception:
/* Handle exception, only accepted source is ecall */
sll a0, a0, 1
li a1, RISCV_IRQ_ECALLS * 2
bne a0, a1, .Lmtrap
/* Handle ecall */
mv a0, sp
jal x1, sbi_mcall_handle
csrr a0, mepc
addi a0, a0, 4
csrw mepc, a0
j 1b
/* An unhandled trap to M-mode: this is an error and we cannot proceed */
.Lmtrap:
csrr a0, mcause /* Interrupt cause [arg0] */
csrr a1, mepc /* Interrupt PC (instruction) [arg1] */
jal x1, sbi_mexception
j __start
.Lmtraploop:
/* If we somehow get here, prevent the software from running away */
nop
nop
j .Lmtraploop
/*****************************************************************************
* Name: m_intstackalloc / m_intstacktop
*
* Description:
* Allocate separate stack(s) for machine mode interrupts, only if kernel
* runs in S-mode. Separate stacks are needed as M-mode interrupts can
* pre-empt S-mode interrupts.
*
****************************************************************************/
#define STACK_ALLOC_SIZE (MMODE_IRQSTACK * CONFIG_SMP_NCPUS)
.bss
.balign 16
.global g_mintstackalloc
.global g_mintstacktop
.type g_mintstackalloc, object
.type g_mintstacktop, object
g_mintstackalloc:
.skip STACK_ALIGN_UP(STACK_ALLOC_SIZE)
g_mintstacktop:
.size g_mintstacktop, 0
.size g_mintstackalloc, STACK_ALIGN_DOWN(STACK_ALLOC_SIZE)

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/****************************************************************************
* arch/risc-v/src/nuttsbi/sbi_start.c
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <nuttx/compiler.h>
#include <nuttx/irq.h>
#include <assert.h>
#include "riscv_internal.h"
#include "sbi_internal.h"
/****************************************************************************
* Private Functions
****************************************************************************/
static void __trap_vec_tmp(void) noreturn_function;
static void __trap_vec_tmp(void)
{
for (; ; )
{
asm("WFI");
}
}
/****************************************************************************
* Private Data
****************************************************************************/
extern void __start_s(void);
/****************************************************************************
* Public Functions
****************************************************************************/
void sbi_start(void)
{
uintptr_t reg;
uintptr_t hartid;
/* Read hart ID */
hartid = READ_CSR(mhartid);
/* Set mscratch, mtimer */
sbi_mscratch_assign(hartid);
sbi_init_mtimer(MTIMER_TIME_BASE, MTIMER_CMP_BASE);
/* Setup system to enter S-mode */
reg = READ_CSR(mstatus);
reg &= ~MSTATUS_MPPM; /* Clear MPP */
reg &= ~MSTATUS_MPIE; /* Clear MPIE */
reg &= ~MSTATUS_TW; /* Do not trap WFI */
reg &= ~MSTATUS_TSR; /* Do not trap sret */
reg &= ~MSTATUS_TVM; /* Allow satp writes from S-mode */
reg |= MSTATUS_SUM; /* Allow supervisor to access user memory */
reg |= MSTATUS_MPPS; /* Set next context = supervisor */
/* Setup next context */
WRITE_CSR(mstatus, reg);
/* Setup a temporary S-mode interrupt vector */
WRITE_CSR(stvec, __trap_vec_tmp);
/* Delegate interrupts */
reg = (MIP_SSIP | MIP_STIP | MIP_SEIP);
WRITE_CSR(mideleg, reg);
/* Delegate exceptions (all of them) */
reg = ((1 << RISCV_IRQ_IAMISALIGNED) |
(1 << RISCV_IRQ_INSTRUCTIONPF) |
(1 << RISCV_IRQ_LOADPF) |
(1 << RISCV_IRQ_STOREPF) |
(1 << RISCV_IRQ_ECALLU));
WRITE_CSR(medeleg, reg);
/* Enable access to all counters for S- and U-mode */
WRITE_CSR(mcounteren, UINT32_C(~0));
WRITE_CSR(scounteren, UINT32_C(~0));
/* Set program counter to __start_s */
WRITE_CSR(mepc, __start_s);
/* Open everything for PMP */
WRITE_CSR(pmpaddr0, -1);
WRITE_CSR(pmpcfg0, (PMPCFG_A_NAPOT | PMPCFG_R | PMPCFG_W | PMPCFG_X));
/* Then jump to the S-mode start function */
register long r0 asm("a0") = (long) hartid;
__asm__ __volatile__("mret" : : "r"(r0));
PANIC();
}

39
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/****************************************************************************
* arch/risc-v/src/nuttsbi/sbi_machine_vectors.S
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
.section .text
.balign 8
.global __mtrap_vec
/****************************************************************************
* Name: __mtrap_vec
*
* Description:
* All M-mode exceptions and interrupts will be handled from here.
*
****************************************************************************/
__mtrap_vec:
j machine_trap
nop