vsstatus

Virtual Supervisor Status

The vsstatus register tracks and controls the hart’s current operating state.

It is VS-mode’s version of sstatus, and substitutes for it when in VS-mode (i.e., in VS-mode CSR address 0x100 is vsstatus, not sstatus).

Unlike the relationship between sstatus and mstatus, none of the bits in vsstatus are aliases of another field.

Attributes

CSR Address	0x200
Virtual CSR Address	0x100
Defining extension	H, version >= 0
Length	64-bit
Privilege Mode	VS

CSR Address

0x200

Virtual CSR Address

0x100

Defining extension

H, version >= 0

Length

64-bit

Privilege Mode

Format

Figure 1. vsstatus format

Field Summary

Name Location Type Reset Value

Name	Location	Type	Reset Value
`SD`	63	RO-H	UNDEFINED_LEGAL
`UXL`	33:32	RO	64
`MXR`	19	RW	UNDEFINED_LEGAL
`SUM`	18	RW	UNDEFINED_LEGAL
`XS`	16:15	RO	0
`FS`	14:13	RW-H	UNDEFINED_LEGAL
`VS`	10:9	RW-H	UNDEFINED_LEGAL
`SPP`	8	RW-H	UNDEFINED_LEGAL
`UBE`	6	RO	0
`SPIE`	5	RW-H	UNDEFINED_LEGAL
`SIE`	1	RW-H	UNDEFINED_LEGAL

SD

RO-H

UNDEFINED_LEGAL

UXL

33:32

MXR

UNDEFINED_LEGAL

SUM

UNDEFINED_LEGAL

XS

16:15

FS

14:13

RW-H

UNDEFINED_LEGAL

VS

10:9

RW-H

UNDEFINED_LEGAL

SPP

RW-H

UNDEFINED_LEGAL

UBE

SPIE

RW-H

UNDEFINED_LEGAL

SIE

RW-H

UNDEFINED_LEGAL

Fields

`SD`

Location: vsstatus[63]
Description: State Dirty

Read-only bit that summarizes whether any of the vsstatus.FS, vsstatus.VS, or vsstatus.XS fields signal the presence of some dirty state (i.e., any of them hold the value 11).

This bit is not an alias of mstatus.SD since it only reflects the state visible to VS-mode (e.g., status.FS does not affect vsstatus.SD).
Type

RO-H	Read-Only with Hardware update Writes are ignored. Reads reflect a value dynamically generated by hardware.

Reset value: UNDEFINED_LEGAL

`UXL`

Location: vsstatus[33:32]
Description: VU-mode XLEN

Sets the effective XLEN for VU-mode (0 = 32-bit, 1 = 64-bit, 2 = 128-bit).

Since the hart only supports VUXLEN==32, this is hardwired to 0.

Since the hart only supports VUXLEN==64, this is hardwired to 1.
Type

RO	Read-Only Field has a hardwired value that does not change. Writes to an RO field are ignored.

Reset value: 64

`MXR`

Location

vsstatus[19]

Description

Make eXecutable Readable

Makes it possible to read executable pages when loading from effective VU-mode or VS-mode (normally, executable pages are not readable).

When 1, load in effective VU-mode or VS-mode from pages marked readable or executable are allowed as long as the page is marked readable (or executable and status.MXR is set) in the G-stage translation.
When 0, load in effective VU-mode or VS-mode from pages marked executable raise a Page Fault exception (unless sstatus.MXR is also set, in which case the above applies).

'vsstatus.MXR' affects all loads that operate under effective VU-mode or VS-mode:
All loads in VU-mode
All loads in VS-mode
Loads in M-mode when mstatus.MPRV == 1, mstatus.MPV == 1, and mstatus.MPP[1] == 0
Loads generated by one of the hlv.* instructions.

Type

RW	Read-Write Field is writable by software. Any value that fits in the field is acceptable and shall be retained for subsequent reads.

Reset value: UNDEFINED_LEGAL

`SUM`

Location

vsstatus[18]

Description

permit Supervisor Memory Access

Allows VS-mode to read user pages.

Applies to the following loads and stores:

All loads and stores in VS-mode.
All loads and stores in M-mode when mstatus.MPRV == 1, mstatus.MPP == 1, and mstatus.MPV == 1
Loads and stores generated by one of the hlv., hlvx., or hsv.* instructions.

When vsstatus.SUM is 0, the loads and stores from the above categories cause an Illegal Instruction exception if they access a user page during VS-level translation. Otherwise, a load or store from the above categories is permitted to acess a user page during VS-level translation.

Type

RW	Read-Write Field is writable by software. Any value that fits in the field is acceptable and shall be retained for subsequent reads.

Reset value: UNDEFINED_LEGAL

`XS`

Location: vsstatus[16:15]
Description: Custom (X) extension context Status

Summarizes the current state of any custom extension state. Either 0 - Off, 1 - Initial, 2 - Clean, 3 - Dirty. Since there are no custom extensions, this field is read-only 0.
Type

RO	Read-Only Field has a hardwired value that does not change. Writes to an RO field are ignored.

Reset value: 0

`FS`

Location: vsstatus[14:13]
Description: Floating point context status

When 0, floating point instructions (from F and D extensions) in VS-mode or VU-mode are disabled, and cause ILLEGAL INSTRUCTION exceptions. Floating point instructions in all modes, including VS-mode and VU-mode, are similarly disabled when mstatus.FS is clear.

When a floating point register, or the fcsr register is written in VS-mode or VU-mode, vsstatus.FS is written with the value 3.

Values 1 and 2 are valid write values for software, but are not interpreted by hardware other than to possibly enable a previously-disabled floating point unit.
Type

RW-H	Read-Write with Hardware update Field is writable by software. Any value that fits in the field is acceptable. Hardware also updates the field without an explicit software write.

Reset value: UNDEFINED_LEGAL

`VS`

Location: vsstatus[10:9]
Description: Vector context status

When 0, vector instructions (from the V extension) are disabled, and cause ILLEGAL INSTRUCTION exceptions. When a vector register or vector CSR is written, VS obtains the value 3. Values 1 and 2 are valid write values for software, but are not interpreted by hardware other than to possibly enable a previously-disabled vector unit.
Type

RW-H	Read-Write with Hardware update Field is writable by software. Any value that fits in the field is acceptable. Hardware also updates the field without an explicit software write.

Reset value: UNDEFINED_LEGAL

`SPP`

Location: vsstatus[8]
Description: VS-mode Previous Privilege

Written with the prior nominal privilege level (i.e., 0 for VU-mode and 1 for VS-mode) when entering VS-mode from an exception/interrupt. Can also be written by software without immediate side-effect.

On a return from an exception from VS-mode, the machine will enter the nominal privilege level stored in vsstatus.SPP.
Type

RW-H	Read-Write with Hardware update Field is writable by software. Any value that fits in the field is acceptable. Hardware also updates the field without an explicit software write.

Reset value: UNDEFINED_LEGAL

`UBE`

Location: vsstatus[6]
Description: VU-mode Big Endian

Controls the endianness of VU-mode (0 = little, 1 = big).

Since the CPU does not support big endian, this is hardwired to 0.

Since the CPU does not support big endian, this is hardwired to 1.
Type

RO	Read-Only Field has a hardwired value that does not change. Writes to an RO field are ignored.

Reset value: 0

`SPIE`

Location

vsstatus[5]

Description

VS-mode Previous Interrupt Enable

Written by hardware in two cases:

Written with prior value of vsstatus.SIE when entering VS-mode from an exception/interrupt.
Writen with the value 1 when returning from an exception in VS-mode (via the sret instruction).

Can also be written by software without immediate side effect.

Other than serving as a record of nested traps as described above, vsstatus.SPIE does not affect execution.

Type

RW-H	Read-Write with Hardware update Field is writable by software. Any value that fits in the field is acceptable. Hardware also updates the field without an explicit software write.

Reset value: UNDEFINED_LEGAL

`SIE`

Location

vsstatus[1]

Description

VS-mode Interrupt Enable

Written by hardware in two cases:

Written with the value 0 when entering VS-mode from an exception/interrupt.
Written with the prior value of vsstatus.SPIE when returning from an exeception in VS-mode (via sret).

Affects execution by:
When 0, all VS-mode interrupts are disabled when the current privilege level is VS ((H)S-mode and M-mode interrupts are still enabled).
When 1, VS-mode interrupts that are not otherwise disabled with a field in vsie are enabled.

Type

RW-H	Read-Write with Hardware update Field is writable by software. Any value that fits in the field is acceptable. Hardware also updates the field without an explicit software write.

Reset value: UNDEFINED_LEGAL