/*
* FreeRTOS Kernel <DEVELOPMENT BRANCH>
* Copyright (C) 2021 Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* SPDX-License-Identifier: MIT
*
* Permission is hereby granted, free of charge, to any person obtaining a copy of
* this software and associated documentation files (the "Software"), to deal in
* the Software without restriction, including without limitation the rights to
* use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
* the Software, and to permit persons to whom the Software is furnished to do so,
* subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
* FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
* COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
* IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*
* https://www.FreeRTOS.org
* https://github.com/FreeRTOS
*
*/
/*
* The FreeRTOS kernel's RISC-V port is split between the the code that is
* common across all currently supported RISC-V chips (implementations of the
* RISC-V ISA), and code which tailors the port to a specific RISC-V chip:
*
* + The code that is common to all RISC-V chips is implemented in
* FreeRTOS\Source\portable\GCC\RISC-V-RV32\portASM.S. There is only one
* portASM.S file because the same file is used no matter which RISC-V chip is
* in use.
*
* + The code that tailors the kernel's RISC-V port to a specific RISC-V
* chip is implemented in freertos_risc_v_chip_specific_extensions.h. There
* is one freertos_risc_v_chip_specific_extensions.h that can be used with any
* RISC-V chip that both includes a standard CLINT and does not add to the
* base set of RISC-V registers. There are additional
* freertos_risc_v_chip_specific_extensions.h files for RISC-V implementations
* that do not include a standard CLINT or do add to the base set of RISC-V
* registers.
*
* CARE MUST BE TAKEN TO INCLDUE THE CORRECT
* freertos_risc_v_chip_specific_extensions.h HEADER FILE FOR THE CHIP
* IN USE. To include the correct freertos_risc_v_chip_specific_extensions.h
* header file ensure the path to the correct header file is in the assembler's
* include path.
*
* This freertos_risc_v_chip_specific_extensions.h is for use on RISC-V chips
* that include a standard CLINT and do not add to the base set of RISC-V
* registers.
*
*/
#include "portContext.h"
/* Check the freertos_risc_v_chip_specific_extensions.h and/or command line
definitions. */
#if defined( portasmHAS_CLINT ) && defined( portasmHAS_MTIME )
#error The portasmHAS_CLINT constant has been deprecated. Please replace it with portasmHAS_MTIME. portasmHAS_CLINT and portasmHAS_MTIME cannot both be defined at once. See https://www.FreeRTOS.org/Using-FreeRTOS-on-RISC-V.html
#endif
#ifdef portasmHAS_CLINT
#warning The portasmHAS_CLINT constant has been deprecated. Please replace it with portasmHAS_MTIME and portasmHAS_SIFIVE_CLINT. For now portasmHAS_MTIME and portasmHAS_SIFIVE_CLINT are derived from portasmHAS_CLINT. See https://www.FreeRTOS.org/Using-FreeRTOS-on-RISC-V.html
#define portasmHAS_MTIME portasmHAS_CLINT
#define portasmHAS_SIFIVE_CLINT portasmHAS_CLINT
#endif
#ifndef portasmHAS_MTIME
#error freertos_risc_v_chip_specific_extensions.h must define portasmHAS_MTIME to either 1 (MTIME clock present) or 0 (MTIME clock not present). See https://www.FreeRTOS.org/Using-FreeRTOS-on-RISC-V.html
#endif
#ifndef portasmHAS_SIFIVE_CLINT
#define portasmHAS_SIFIVE_CLINT 0
#endif
/* CSR definitions. */
#define CSR_MSTATUS 0x300
#define CSR_MTVEC 0x305
#define CSR_MEPC 0x341
#define CSR_MCAUSE 0x342
PUBLIC xPortStartFirstTask
PUBLIC pxPortInitialiseStack
PUBLIC freertos_risc_v_trap_handler
PUBLIC freertos_risc_v_exception_handler
PUBLIC freertos_risc_v_interrupt_handler
PUBLIC freertos_risc_v_mtimer_interrupt_handler
EXTERN vTaskSwitchContext
EXTERN xTaskIncrementTick
EXTERN pullMachineTimerCompareRegister
EXTERN pullNextTime
EXTERN uxTimerIncrementsForOneTick /* size_t type so 32-bit on 32-bit core and 64-bits on 64-bit core. */
EXTERN xTaskReturnAddress
PUBWEAK freertos_risc_v_application_exception_handler
PUBWEAK freertos_risc_v_application_interrupt_handler
/*-----------------------------------------------------------*/
SECTION `.text`:CODE:NOROOT(2)
CODE
portUPDATE_MTIMER_COMPARE_REGISTER MACRO
load_x a0, pullMachineTimerCompareRegister /* Load address of compare register into a0. */
load_x a1, pullNextTime /* Load the address of ullNextTime into a1. */
#if( __riscv_xlen == 32 )
/* Update the 64-bit mtimer compare match value in two 32-bit writes. */
li a4, -1
lw a2, 0(a1) /* Load the low word of ullNextTime into a2. */
lw a3, 4(a1) /* Load the high word of ullNextTime into a3. */
sw a4, 0(a0) /* Low word no smaller than old value to start with - will be overwritten below. */
sw a3, 4(a0) /* Store high word of ullNextTime into compare register. No smaller than new value. */
sw a2, 0(a0) /* Store low word of ullNextTime into compare register. */
lw t0, uxTimerIncrementsForOneTick /* Load the value of ullTimerIncrementForOneTick into t0 (could this be optimized by storing in an array next to pullNextTime?). */
add a4, t0, a2 /* Add the low word of ullNextTime to the timer increments for one tick (assumes timer increment for one tick fits in 32-bits). */
sltu t1, a4, a2 /* See if the sum of low words overflowed (what about the zero case?). */
add t2, a3, t1 /* Add overflow to high word of ullNextTime. */
sw a4, 0(a1) /* Store new low word of ullNextTime. */
sw t2, 4(a1) /* Store new high word of ullNextTime. */
#endif /* __riscv_xlen == 32 */
#if( __riscv_xlen == 64 )
/* Update the 64-bit mtimer compare match value. */
ld t2, 0(a1) /* Load ullNextTime into t2. */
sd t2, 0(a0) /* Store ullNextTime into compare register. */
ld t0, uxTimerIncrementsForOneTick /* Load the value of ullTimerIncrementForOneTick into t0 (could this be optimized by storing in an array next to pullNextTime?). */
add t4, t0, t2 /* Add ullNextTime to the timer increments for one tick. */
sd t4, 0(a1) /* Store ullNextTime. */
#endif /* __riscv_xlen == 64 */
ENDM
/*-----------------------------------------------------------*/
/*
* Unlike other ports pxPortInitialiseStack() is written in assembly code as it
* needs access to the portasmADDITIONAL_CONTEXT_SIZE constant. The prototype
* for the function is as per the other ports:
* StackType_t *pxPortInitialiseStack( StackType_t *pxTopOfStack, TaskFunction_t pxCode, void *pvParameters );
*
* As per the standard RISC-V ABI pxTopcOfStack is passed in in a0, pxCode in
* a1, and pvParameters in a2. The new top of stack is passed out in a0.
*
* RISC-V maps registers to ABI names as follows (X1 to X31 integer registers
* for the 'I' profile, X1 to X15 for the 'E' profile, currently I assumed).
*
* Register ABI Name Description Saver
* x0 zero Hard-wired zero -
* x1 ra Return address Caller
* x2 sp Stack pointer Callee
* x3 gp Global pointer -
* x4 tp Thread pointer -
* x5-7 t0-2 Temporaries Caller
* x8 s0/fp Saved register/Frame pointer Callee
* x9 s1 Saved register Callee
* x10-11 a0-1 Function Arguments/return values Caller
* x12-17 a2-7 Function arguments Caller
* x18-27 s2-11 Saved registers Callee
* x28-31 t3-6 Temporaries Caller
*
* The RISC-V context is saved t FreeRTOS tasks in the following stack frame,
* where the global and thread pointers are currently assumed to be constant so
* are not saved:
*
* mstatus
* xCriticalNesting
* x31
* x30
* x29
* x28
* x27
* x26
* x25
* x24
* x23
* x22
* x21
* x20
* x19
* x18
* x17
* x16
* x15
* x14
* x13
* x12
* x11
* pvParameters
* x9
* x8
* x7
* x6
* x5
* portTASK_RETURN_ADDRESS
* [chip specific registers go here]
* pxCode
*/
pxPortInitialiseStack:
csrr t0, CSR_MSTATUS /* Obtain current mstatus value. */
andi t0, t0, ~0x8 /* Ensure interrupts are disabled when the stack is restored within an ISR. Required when a task is created after the schedulre has been started, otherwise interrupts would be disabled anyway. */
addi t1, x0, 0x188 /* Generate the value 0x1880, which are the MPIE and MPP bits to set in mstatus. */
slli t1, t1, 4
or t0, t0, t1 /* Set MPIE and MPP bits in mstatus value. */
addi a0, a0, -portWORD_SIZE
store_x t0, 0(a0) /* mstatus onto the stack. */
addi a0, a0, -portWORD_SIZE /* Space for critical nesting count. */
store_x x0, 0(a0) /* Critical nesting count starts at 0 for every task. */
#ifdef __riscv_32e
addi a0, a0, -(6 * portWORD_SIZE) /* Space for registers x10-15. */
#else
addi a0, a0, -(22 * portWORD_SIZE) /* Space for registers x10-x31. */
#endif
store_x a2, 0(a0) /* Task parameters (pvParameters parameter) goes into register X10/a0 on the stack. */
addi a0, a0, -(6 * portWORD_SIZE) /* Space for registers x5-x9 + taskReturnAddress. */
load_x t0, xTaskReturnAddress
store_x t0, 0(a0) /* Return address onto the stack. */
addi t0, x0, portasmADDITIONAL_CONTEXT_SIZE /* The number of chip specific additional registers. */
chip_specific_stack_frame: /* First add any chip specific registers to the stack frame being created. */
beq t0, x0, no_more_regs /* No more chip specific registers to save. */
addi a0, a0, -portWORD_SIZE /* Make space for chip specific register. */
store_x x0, 0(a0) /* Give the chip specific register an initial value of zero. */
addi t0, t0, -1 /* Decrement the count of chip specific registers remaining. */
j chip_specific_stack_frame /* Until no more chip specific registers. */
no_more_regs:
addi a0, a0, -portWORD_SIZE
store_x a1, 0(a0) /* mret value (pxCode parameter) onto the stack. */
ret
/*-----------------------------------------------------------*/
xPortStartFirstTask:
load_x sp, pxCurrentTCB /* Load pxCurrentTCB. */
load_x sp, 0( sp ) /* Read sp from first TCB member. */
load_x x1, 0( sp ) /* Note for starting the scheduler the exception return address is used as the function return address. */
portasmRESTORE_ADDITIONAL_REGISTERS /* Defined in freertos_risc_v_chip_specific_extensions.h to restore any registers unique to the RISC-V implementation. */
load_x x7, 4 * portWORD_SIZE( sp ) /* t2 */
load_x x8, 5 * portWORD_SIZE( sp ) /* s0/fp */
load_x x9, 6 * portWORD_SIZE( sp ) /* s1 */
load_x x10, 7 * portWORD_SIZE( sp ) /* a0 */
load_x x11, 8 * portWORD_SIZE( sp ) /* a1 */
load_x x12, 9 * portWORD_SIZE( sp ) /* a2 */
load_x x13, 10 * portWORD_SIZE( sp ) /* a3 */
load_x x14, 11 * portWORD_SIZE( sp ) /* a4 */
load_x x15, 12 * portWORD_SIZE( sp ) /* a5 */
#ifndef __riscv_32e
load_x x16, 13 * portWORD_SIZE( sp ) /* a6 */
load_x x17, 14 * portWORD_SIZE( sp ) /* a7 */
load_x x18, 15 * portWORD_SIZE( sp ) /* s2 */
load_x x19, 16 * portWORD_SIZE( sp ) /* s3 */
load_x x20, 17 * portWORD_SIZE( sp ) /* s4 */
load_x x21, 18 * portWORD_SIZE( sp ) /* s5 */
load_x x22, 19 * portWORD_SIZE( sp ) /* s6 */
load_x x23, 20 * portWORD_SIZE( sp ) /* s7 */
load_x x24, 21 * portWORD_SIZE( sp ) /* s8 */
load_x x25, 22 * portWORD_SIZE( sp ) /* s9 */
load_x x26, 23 * portWORD_SIZE( sp ) /* s10 */
load_x x27, 24 * portWORD_SIZE( sp ) /* s11 */
load_x x28, 25 * portWORD_SIZE( sp ) /* t3 */
load_x x29, 26 * portWORD_SIZE( sp ) /* t4 */
load_x x30, 27 * portWORD_SIZE( sp ) /* t5 */
load_x x31, 28 * portWORD_SIZE( sp ) /* t6 */
#endif
load_x x5, portCRITICAL_NESTING_OFFSET * portWORD_SIZE( sp ) /* Obtain xCriticalNesting value for this task from task's stack. */
load_x x6, pxCriticalNesting /* Load the address of xCriticalNesting into x6. */
store_x x5, 0( x6 ) /* Restore the critical nesting value for this task. */
load_x x5, portMSTATUS_OFFSET * portWORD_SIZE( sp ) /* Initial mstatus into x5 (t0). */
addi x5, x5, 0x08 /* Set MIE bit so the first task starts with interrupts enabled - required as returns with ret not eret. */
csrrw x0, CSR_MSTATUS, x5 /* Interrupts enabled from here! */
load_x x5, 2 * portWORD_SIZE( sp ) /* Initial x5 (t0) value. */
load_x x6, 3 * portWORD_SIZE( sp ) /* Initial x6 (t1) value. */
addi sp, sp, portCONTEXT_SIZE
ret
/*-----------------------------------------------------------*/
freertos_risc_v_application_exception_handler:
csrr t0, CSR_MCAUSE /* For viewing in the debugger only. */
csrr t1, CSR_MEPC /* For viewing in the debugger only */
csrr t2, CSR_MSTATUS /* For viewing in the debugger only */
j $
/*-----------------------------------------------------------*/
freertos_risc_v_application_interrupt_handler:
csrr t0, CSR_MCAUSE /* For viewing in the debugger only. */
csrr t1, CSR_MEPC /* For viewing in the debugger only */
csrr t2, CSR_MSTATUS /* For viewing in the debugger only */
j $
/*-----------------------------------------------------------*/
SECTION `.text.freertos_risc_v_exception_handler`:CODE:NOROOT(2)
CODE
freertos_risc_v_exception_handler:
portcontextSAVE_EXCEPTION_CONTEXT
/* a0 now contains mcause. */
li t0, 11 /* 11 == environment call. */
bne a0, t0, other_exception /* Not an M environment call, so some other exception. */
call vTaskSwitchContext
portcontextRESTORE_CONTEXT
other_exception:
call freertos_risc_v_application_exception_handler
portcontextRESTORE_CONTEXT
/*-----------------------------------------------------------*/
SECTION `.text.freertos_risc_v_interrupt_handler`:CODE:NOROOT(2)
CODE
freertos_risc_v_interrupt_handler:
portcontextSAVE_INTERRUPT_CONTEXT
call freertos_risc_v_application_interrupt_handler
portcontextRESTORE_CONTEXT
/*-----------------------------------------------------------*/
SECTION `.text.freertos_risc_v_mtimer_interrupt_handler`:CODE:NOROOT(2)
CODE
freertos_risc_v_mtimer_interrupt_handler:
portcontextSAVE_INTERRUPT_CONTEXT
portUPDATE_MTIMER_COMPARE_REGISTER
call xTaskIncrementTick
beqz a0, exit_without_context_switch /* Don't switch context if incrementing tick didn't unblock a task. */
call vTaskSwitchContext
exit_without_context_switch:
portcontextRESTORE_CONTEXT
/*-----------------------------------------------------------*/
SECTION `.text.freertos_risc_v_trap_handler`:CODE:NOROOT(8)
CODE
freertos_risc_v_trap_handler:
portcontextSAVE_CONTEXT_INTERNAL
csrr a0, CSR_MCAUSE
csrr a1, CSR_MEPC
bge a0, x0, synchronous_exception
asynchronous_interrupt:
store_x a1, 0( sp ) /* Asynchronous interrupt so save unmodified exception return address. */
load_x sp, xISRStackTop /* Switch to ISR stack. */
j handle_interrupt
synchronous_exception:
addi a1, a1, 4 /* Synchronous so update exception return address to the instruction after the instruction that generated the exeption. */
store_x a1, 0( sp ) /* Save updated exception return address. */
load_x sp, xISRStackTop /* Switch to ISR stack. */
j handle_exception
handle_interrupt:
#if( portasmHAS_MTIME != 0 )
test_if_mtimer: /* If there is a CLINT then the mtimer is used to generate the tick interrupt. */
addi t0, x0, 1
slli t0, t0, __riscv_xlen - 1 /* LSB is already set, shift into MSB. Shift 31 on 32-bit or 63 on 64-bit cores. */
addi t1, t0, 7 /* 0x8000[]0007 == machine timer interrupt. */
bne a0, t1, application_interrupt_handler
portUPDATE_MTIMER_COMPARE_REGISTER
call xTaskIncrementTick
beqz a0, processed_source /* Don't switch context if incrementing tick didn't unblock a task. */
call vTaskSwitchContext
j processed_source
#endif /* portasmHAS_MTIME */
application_interrupt_handler:
call freertos_risc_v_application_interrupt_handler
j processed_source
handle_exception:
/* a0 contains mcause. */
li t0, 11 /* 11 == environment call. */
bne a0, t0, application_exception_handler /* Not an M environment call, so some other exception. */
call vTaskSwitchContext
j processed_source
application_exception_handler:
call freertos_risc_v_application_exception_handler
j processed_source /* No other exceptions handled yet. */
processed_source:
portcontextRESTORE_CONTEXT
/*-----------------------------------------------------------*/