stvec

Supervisor Trap Vector

Controls where traps jump.

Attributes

CSR Address	0x105
Defining extension	S, version >= 0
Length	64-bit
Privilege Mode	S

CSR Address

0x105

Defining extension

S, version >= 0

Length

64-bit

Privilege Mode

Format

Figure 1. stvec format

Field Summary

Name Location Type Reset Value

Name	Location	Type	Reset Value
`BASE`	63:2	RW-R	UNDEFINED_LEGAL
`MODE`	1:0	RW-R	0

BASE

63:2

RW-R

UNDEFINED_LEGAL

MODE

1:0

RW-R

Fields

`BASE`

Location: stvec[63:2]
Description: Bit 63:0 of the virtual address of the exception vector for any trap taken into S-mode.

If the base address is written with a non-cannonical address (i.e., bits 63:49 do not match bit 48), the write should be ignored.
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

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.

return csr_value.BASE;

`MODE`

Location: stvec[1:0]
Description: Vectoring mode for asynchronous interrupts.

0 - Direct, 1 - Vectored

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

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

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 (STVEC_MODE_DIRECT && csr_value.MODE == 0) {
  return 0;
} else if (STVEC_MODE_VECTORED && csr_value.MODE == 1) {
  return 1;
} else {
  return UNDEFINED_LEGAL_DETERMINISTIC;
}