entry.S

// See LICENSE for license details

#ifndef ENTRY_S
#define ENTRY_S

#include "riscv_encoding.h"
#include "riscv_bits.h"
#include "n22_eclic.h"
#include "n22_tmr.h"

###############################################
###############################################
# Disable Interrupt
#
.macro DISABLE_MIE
  csrc CSR_MSTATUS, MSTATUS_MIE
.endm


###############################################
###############################################
#Save caller registers
.macro SAVE_CONTEXT

  STORE x1,  0*REGBYTES(sp)
  STORE x5,  1*REGBYTES(sp)
  STORE x6,  2*REGBYTES(sp)
  STORE x7,  3*REGBYTES(sp)
  STORE x10, 4*REGBYTES(sp)
  STORE x11, 5*REGBYTES(sp)
  STORE x12, 6*REGBYTES(sp)
  STORE x13, 7*REGBYTES(sp)
  STORE x14, 8*REGBYTES(sp)
  STORE x15, 9*REGBYTES(sp)
  STORE x16, 10*REGBYTES(sp)
  STORE x17, 11*REGBYTES(sp)
  STORE x28, 12*REGBYTES(sp)
  STORE x29, 13*REGBYTES(sp)
  STORE x30, 14*REGBYTES(sp)
  STORE x31, 15*REGBYTES(sp)
.endm


###############################################
###############################################
#restore caller registers
.macro RESTORE_CONTEXT
  LOAD x1,  0*REGBYTES(sp)
  LOAD x5,  1*REGBYTES(sp)
  LOAD x6,  2*REGBYTES(sp)
  LOAD x7,  3*REGBYTES(sp)
  LOAD x10, 4*REGBYTES(sp)
  LOAD x11, 5*REGBYTES(sp)
  LOAD x12, 6*REGBYTES(sp)
  LOAD x13, 7*REGBYTES(sp)
  LOAD x14, 8*REGBYTES(sp)
  LOAD x15, 9*REGBYTES(sp)
  LOAD x16, 10*REGBYTES(sp)
  LOAD x17, 11*REGBYTES(sp)
  LOAD x28, 12*REGBYTES(sp)
  LOAD x29, 13*REGBYTES(sp)
  LOAD x30, 14*REGBYTES(sp)
  LOAD x31, 15*REGBYTES(sp)

.endm

###############################################
###############################################
#restore caller registers
.macro RESTORE_CONTEXT_EXCPT_X5
  LOAD x1,  0*REGBYTES(sp)
  LOAD x6,  2*REGBYTES(sp)
  LOAD x7,  3*REGBYTES(sp)
  LOAD x10, 4*REGBYTES(sp)
  LOAD x11, 5*REGBYTES(sp)
  LOAD x12, 6*REGBYTES(sp)
  LOAD x13, 7*REGBYTES(sp)
  LOAD x14, 8*REGBYTES(sp)
  LOAD x15, 9*REGBYTES(sp)
  LOAD x16, 10*REGBYTES(sp)
  LOAD x17, 11*REGBYTES(sp)
  LOAD x28, 12*REGBYTES(sp)
  LOAD x29, 13*REGBYTES(sp)
  LOAD x30, 14*REGBYTES(sp)
  LOAD x31, 15*REGBYTES(sp)

.endm

###############################################
###############################################
#restore caller registers
.macro RESTORE_CONTEXT_ONLY_X5
  LOAD x5,  1*REGBYTES(sp)
.endm

###############################################
###############################################
# Save the mepc and mstatus
#
.macro SAVE_MEPC_MSTATUS
  csrr x5, CSR_MEPC
  STORE x5,  16*REGBYTES(sp)
  csrr x5, CSR_MSTATUS
  STORE x5,  17*REGBYTES(sp)
  csrr x5, CSR_MXSTATUS
  STORE x5,  18*REGBYTES(sp)
.endm

###############################################
###############################################
# Restore the mepc and mstatus
#
.macro RESTORE_MEPC_MSTATUS
  LOAD x5,  16*REGBYTES(sp)
  csrw CSR_MEPC, x5
  LOAD x5,  17*REGBYTES(sp)
  csrw CSR_MSTATUS, x5
  LOAD x5,  18*REGBYTES(sp)
  csrw CSR_MXSTATUS, x5
.endm

###############################################
###############################################
// trap entry point
//
  .section      .text.entry
  .align 6 // In ECLIC mode, the trap entry must be 64bytes aligned
  .global trap_entry
.weak trap_entry
trap_entry:
   // Allocate the stack space
  addi sp, sp, -19*REGBYTES

  // Save the caller saving registers (context)
  SAVE_CONTEXT
  // Save the MEPC/MStatus reg
  SAVE_MEPC_MSTATUS

     // Set the function argument
  csrr a0, mcause
  mv a1, sp
     // Call the function
  call handle_trap

  // Restore the MEPC/MStatus reg
  RESTORE_MEPC_MSTATUS
  // Restore the caller saving registers (context)
  RESTORE_CONTEXT

  // De-allocate the stack space
  addi sp, sp, 19*REGBYTES
  // Return to regular code
  mret
###############################################
###############################################
// IRQ entry point
//
  .section      .text.irq
  .align 2
  .global irq_entry
.weak irq_entry
irq_entry: // -------------> This label will be set to MTVT2 register
  // Allocate the stack space
  addi sp, sp, -19*REGBYTES

  SAVE_CONTEXT// Save 16 regs

  //------This special CSR read operation, which is actually use mcause as operand to directly store it to memory
  csrrwi  x0, CSR_PUSHMCAUSE, 16
  //------This special CSR read operation, which is actually use mepc as operand to directly store it to memory
  csrrwi  x0, CSR_PUSHMEPC, 17
  //------This special CSR read operation, which is actually use mxstatus as operand to directly store it to memory
  csrrwi  x0, CSR_PUSHMXSTATUS, 18

service_loop:
  //------This special CSR read/write operation, which is actually Claim the ECLIC to find its pending highest
  // ID, if the ID is not 0, then automatically enable the mstatus.MIE, and jump to its vector-entry-label, and
  // update the link register
  csrrw ra, CSR_MINTSEL_JAL, ra

  RESTORE_CONTEXT_EXCPT_X5

  #---- Critical section with interrupts disabled -----------------------
  DISABLE_MIE # Disable interrupts

  LOAD x5,  18*REGBYTES(sp)
  csrw CSR_MXSTATUS, x5
  LOAD x5,  17*REGBYTES(sp)
  csrw CSR_MEPC, x5
  LOAD x5,  16*REGBYTES(sp)
  csrw CSR_MCAUSE, x5


  RESTORE_CONTEXT_ONLY_X5

  // De-allocate the stack space
  addi sp, sp, 19*REGBYTES
  // Return to regular code
  mret




#endif