mtvec

Machine Trap Vector Control

Controls where traps jump.

Attributes

CSR Address

0x305

Defining extension

Sm

Length

64-bit

Privilege Mode

M

Format

mtvec format
Figure 1. mtvec format

Field Summary

Name Location Type Reset Value

BASE

63:2

RW-R

0

MODE

1:0

[when,"(MTVEC_ACCESS == "ro")"] RO [when,"(MTVEC_ACCESS != "ro")"]

[when,"$array_size(MTVEC_MODES) == 1"] RO

[when,"$array_size(MTVEC_MODES) != 1"] RW-R

UNDEFINED_LEGAL

Fields

BASE

Location

mtvec[63:2]

Description

Bits [MXLEN-1:2] of the exception vector physical address for any trap taken in M-mode.

The implementation physical memory map may resitrict which values are legal in this field.

Type

RW-R

Read-Write Restricted

Field is writable by software. Only certain values are legal. Writing an illegal value into the field is ignored, and the field retains its prior state.
Reset value

0

Software write

This field has special behavior when written by software (e.g., through csrrw).

When software tries to write csr_value, the field will be written with the return value of the function below.

if (csr_value.MODE == 0) {
  return csr_value.BASE;
  return CSR[mtvec].BASE;

  unreachable();
} else if (csr_value.MODE == 1) {
  return csr_value.BASE;
  return CSR[mtvec].BASE;

  unreachable();
} else {
  return CSR[mtvec].BASE;

  unreachable();
}

MODE

Location

mtvec[1:0]

Description

Vectoring mode for asynchronous interrupts.

0 - Direct, 1 - Vectored

When Direct, all synchronous exceptions and asynchronous interrupts jump to (mtvec.BASE << 2).

When Vectored, asynchronous interrupts jump to (mtvec.BASE << 2 + mcause*4) while synchronous exceptions continue to jump to (mtvec.BASE << 2).

Type
Reset value

UNDEFINED_LEGAL

Software write

This field has special behavior when written by software (e.g., through csrrw).

When software tries to write csr_value, the field will be written with the return value of the function below.

if (csr_value.MODE == 0) {
  return csr_value.MODE;
} else if (csr_value.MODE == 1) {
  return csr_value.MODE;
} else {
  return CSR[mtvec].MODE;
}
unreachable();