sireg5

Supervisor Indirect Register Alias 5

Access to sireg5 from M-mode or S-mode while siselect holds a number in a standard-defined and implemented range results in specific behavior that, for each combination of siselect and sireg5, is defined by the extension to which the siselect value is allocated.

Ordinarily, sireg5 will access register state, access read-only 0 state, or, unless executing in a virtual machine (covered in the next section), raise an illegal instruction exception.

Note that the widths of siselect and sireg5 are always the current XLEN rather than SXLEN. Hence, for example, if MXLEN = 64 and SXLEN = 32, then this register is 64 bits when the current privilege mode is M (running RV64 code) but 32 bits when the privilege mode is S (RV32 code).

The behavior upon accessing sireg5 from M-mode or S-mode, while siselect holds a value that is not implemented at supervisor level, is UNSPECIFIED.

It is recommended that implementations raise an illegal instruction exception for such accesses, to facilitate possible emulation (by M-mode) of these accesses.

An extension is considered not to be implemented at supervisor level if machine level has disabled the extension for S-mode, such as by the settings of certain fields in CSR menvcfg, for example.

Attributes

Defining Extension

  • Sscsrind, version >= Sscsrind@1.0.0

CSR Address

0x156

Length

32 when CSR[mstatus].SXL == 0 64 when CSR[mstatus].SXL == 1

Privilege Mode

S

Format

This CSR format changes dynamically.

sireg5 Format when CSR[mstatus].SXL == 0
Figure 1. sireg5 Format when CSR[mstatus].SXL == 0
sireg5 Format when CSR[mstatus].SXL == 1
Figure 2. sireg5 Format when CSR[mstatus].SXL == 1

Field Summary

Name Location Type Reset Value

sireg5.VALUE

* 31:0 when CSR[mstatus].SXL == 0 * 63:0 when CSR[mstatus].SXL == 1

RW

UNDEFINED_LEGAL

Fields

VALUE

Location

  • 31:0 when CSR[mstatus].SXL == 0

  • 63:0 when CSR[mstatus].SXL == 1

Description

The data read from or written to the register selected by the current siselect value.

Type

RW

Reset value

UNDEFINED_LEGAL

Software write

This CSR may store a value that is different from what software attempts to write.

When a software write occurs (e.g., through csrrw), the following determines the written value:

VALUE = Csr handle = indirect_csr_lookup(CSR[siselect].VALUE, 5);
if (!handle.valid) {
  unimplemented_csr($encoding);
}
if (!handle.writable) {
  raise (ExceptionCode::IllegalInstruction, mode(), $encoding);
}
csr_sw_write(handle, csr_value.VALUE);
return csr_hw_read(handle);

Software read

This CSR may return a value that is different from what is stored in hardware.

Csr handle = indirect_csr_lookup(siselect.VALUE, 5);
if (!handle.valid) {
  unimplemented_csr($encoding);
}
return csr_sw_read(handle);