ports/risc-v64/gnu/example_build/erbium/tx_initialize_low_level.S


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/***************************************************************************
 * Copyright (c) 2026 Eclipse ThreadX contributors
 *
 * This program and the accompanying materials are made available under the
 * terms of the MIT License which is available at
 * https://opensource.org/licenses/MIT.
 *
 * AI Disclosure: This file was largely AI-generated by Claude Code (Opus 5.5).
 * The AI-generated portions may be considered public domain (CC0-1.0)
 * and not subject to the project's licence. The human contributor has
 * reviewed and verified that the code is correct.
 *
 * SPDX-License-Identifier: MIT and CC0-1.0
 **************************************************************************/

#include "csr.h"
#include "tx_port.h"

/* Erbium ignores mtvec base bits 11:1, so the trap vector must be 4 KiB
   aligned.  */
    .section .text.trap, "ax", @progbits
    .balign 4096
/**************************************************************************/
/*                                                                        */
/*  FUNCTION                                               RELEASE        */
/*                                                                        */
/*    trap_entry                                         RISC-V64/GNU     */
/*                                                                        */
/*  DESCRIPTION                                                           */
/*                                                                        */
/*    This function is the machine-mode trap vector (direct mode).  It    */
/*    saves the interrupted context, calls trap_handler with mcause,      */
/*    mepc and mtval, and leaves through the ThreadX context restore.     */
/*                                                                        */
/*  INPUT                                                                 */
/*                                                                        */
/*    None                                                                */
/*                                                                        */
/*  OUTPUT                                                                */
/*                                                                        */
/*    None                                                                */
/*                                                                        */
/*  CALLS                                                                 */
/*                                                                        */
/*    _tx_thread_context_save               Save interrupted context      */
/*    trap_handler                          Dispatch the trap             */
/*    _tx_thread_context_restore            Restore or schedule a thread  */
/*                                                                        */
/*  CALLED BY                                                             */
/*                                                                        */
/*    Hardware trap                                                       */
/*                                                                        */
/**************************************************************************/
    .global  trap_entry
    .extern  trap_handler
    .extern  _tx_thread_context_save
    .extern  _tx_thread_context_restore
trap_entry:
    addi    sp, sp, -TX_RISCV_TRAP_FRAME_SIZE       // Interrupt frame from the port contract
    sd      x1, 28*8(sp)                            // Save RA before the call below overwrites it

    call    _tx_thread_context_save

    csrr    a0, mcause
    csrr    a1, mepc
    csrr    a2, mtval
    addi    sp, sp, -16                             // 16 bytes keep sp 16-byte aligned at the call
    sd      ra, 0(sp)
    call    trap_handler
    ld      ra, 0(sp)
    addi    sp, sp, 16

    call    _tx_thread_context_restore
    /* _tx_thread_context_restore does not return.  */
_trap_entry_hang:
    j       _trap_entry_hang


    .section .text
/**************************************************************************/
/*                                                                        */
/*  FUNCTION                                               RELEASE        */
/*                                                                        */
/*    _tx_initialize_low_level                           RISC-V64/GNU     */
/*                                                                        */
/*  DESCRIPTION                                                           */
/*                                                                        */
/*    This function is responsible for any low-level processor            */
/*    initialization, including setting up interrupt vectors, setting     */
/*    up a periodic timer interrupt source, saving the system stack       */
/*    pointer for use in ISR processing later, and finding the first      */
/*    available RAM memory address for tx_application_define.             */
/*                                                                        */
/*  INPUT                                                                 */
/*                                                                        */
/*    None                                                                */
/*                                                                        */
/*  OUTPUT                                                                */
/*                                                                        */
/*    None                                                                */
/*                                                                        */
/*  CALLS                                                                 */
/*                                                                        */
/*    board_init                            Initialize the peripherals    */
/*                                                                        */
/*  CALLED BY                                                             */
/*                                                                        */
/*    _tx_initialize_kernel_enter           ThreadX entry function        */
/*                                                                        */
/**************************************************************************/
/* VOID   _tx_initialize_low_level(VOID)
{  */
    .global  _tx_initialize_low_level              // Strong definition: must beat the port's weak default
    .extern  _end
    .extern  board_init
    .extern  _tx_thread_system_stack_ptr
    .extern  _tx_initialize_unused_memory
_tx_initialize_low_level:
    la      t0, _tx_thread_system_stack_ptr
    sd      sp, 0(t0)                               // Save system stack pointer

    la      t0, _end                                // Pickup first free address
    la      t1, _tx_initialize_unused_memory
    sd      t0, 0(t1)                               // Save unused memory address

    li      t0, MSTATUS_MIE
    csrrc   zero, mstatus, t0                       // Keep interrupts off until the scheduler runs
    li      t0, (MSTATUS_MPP_M | MSTATUS_MPIE)
    csrrs   zero, mstatus, t0                       // mret stays in M-mode with interrupts enabled
    li      t0, (MIE_MTIE | MIE_MEIE)
    csrrs   zero, mie, t0                           // Enable timer and external interrupts

    addi    sp, sp, -16                             // 16 bytes keep sp 16-byte aligned at the call
    sd      ra, 0(sp)
    call    board_init
    ld      ra, 0(sp)
    addi    sp, sp, 16

    la      t0, trap_entry
    csrw    mtvec, t0                               // Direct mode: trap_entry is 4 KiB aligned
    ret
/* }  */