MNRS-BM-BSP/libwrap/semihosting/trap.c

#include <math.h>
#include <stdint.h>
#include <stdlib.h>

#include "encoding.h"

#if defined(SEMIHOSTING)
#define EBREAK_OPCODE 0x00100073
#define EBREAK_MCAUSE 0x00000003

#define SLLI_X0_X0_0X1F_OPCODE 0x01f01013
#define SRAI_X0_X0_0X07_OPCODE 0x40705013

int sh_missing_host = 0;

void trap() { // ToDo: Check why macro CSR_MEPC and others are not
              // resolved
  uint32_t mepc = read_csr(0x341);   // Address of trap
  uint32_t mtval = read_csr(0x343);  // Instruction value of trap
  uint32_t mcause = read_csr(0x342); // Reason for the trap

  if (mcause == EBREAK_MCAUSE && mtval == EBREAK_OPCODE) {
    // This trap was caused by an EBREAK...

    int aligned = ((mepc - 4) & 0x0f) == 0;
    if (aligned && *(uint32_t *)mepc == EBREAK_OPCODE &&
        *(uint32_t *)(mepc - 4) == SLLI_X0_X0_0X1F_OPCODE &&
        *(uint32_t *)(mepc + 4) == SRAI_X0_X0_0X07_OPCODE) {
      // The EBREAK was part of the semihosting call. (See semihosting.c)
      //
      // If a debugger were connected, this would have resulted in a CPU halt,
      // and the debugger would have serviced the the semihosting call.
      //
      // However, the semihosting function was called without a debugger being
      // attached. The best course of action is to simply return from the trap
      // and let the semihosting function continue after the call to EBREAK to
      // prevent the CPU from hanging in the trap handler.
      write_csr(mepc, mepc + 4);

      // Set a global variable to tell the semihosting code the the semihosting
      // call
      // didn't execute on the host.
      sh_missing_host = 1;

      return;
    }

    // EBREAK was not part of a semihosting call. This should not have happened.
    // Hang forever.
    while (1)
      ;
  }

  // Trap was issued for another reason than an EBREAK.
  // Replace the code below with whatever trap handler you'd normally use. (e.g.
  // interrupt processing.)
  while (1)
    ;
}
#endif