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Legacy Extensions (EIDs #0x00 - #0x0F)

The legacy SBI extensions follow a slightly different calling convention as compared to the SBI v0.2 (or higher) specification where:

  • The SBI function ID field in a6 register is ignored because these are encoded as multiple SBI extension IDs.

  • Nothing is returned in a1 register.

  • All registers except a0 must be preserved across an SBI call by the callee.

  • The value returned in a0 register is SBI legacy extension specific.

The page and access faults taken by the SBI implementation while accessing memory on behalf of the supervisor are redirected back to the supervisor with sepc CSR pointing to the faulting ECALL instruction.

The legacy SBI extensions is deprecated in favor of the other extensions listed below.

Extension: Set Timer (EID #0x00)

long sbi_set_timer(uint64_t stime_value)

Programs the clock for next event after stime_value time. This function also clears the pending timer interrupt bit.

If the supervisor wishes to clear the timer interrupt without scheduling the next timer event, it can either request a timer interrupt infinitely far into the future (i.e., (uint64_t)-1), or it can instead mask the timer interrupt by clearing sie.STIE CSR bit.

This SBI call returns 0 upon success or an implementation specific negative error code.

Extension: Console Putchar (EID #0x01)

long sbi_console_putchar(int ch)

Write data present in ch to debug console.

Unlike sbi_console_getchar(), this SBI call will block if there remain any pending characters to be transmitted or if the receiving terminal is not yet ready to receive the byte. However, if the console doesn’t exist at all, then the character is thrown away.

This SBI call returns 0 upon success or an implementation specific negative error code.

Extension: Console Getchar (EID #0x02)

long sbi_console_getchar(void)

Read a byte from debug console.

The SBI call returns the byte on success, or -1 for failure.

Extension: Clear IPI (EID #0x03)

long sbi_clear_ipi(void)

Clears the pending IPIs if any. The IPI is cleared only in the hart for which this SBI call is invoked. sbi_clear_ipi() is deprecated because S-mode code can clear sip.SSIP CSR bit directly.

This SBI call returns 0 if no IPI had been pending, or an implementation specific positive value if an IPI had been pending.

Extension: Send IPI (EID #0x04)

long sbi_send_ipi(const unsigned long *hart_mask)

Send an inter-processor interrupt to all the harts defined in hart_mask. Interprocessor interrupts manifest at the receiving harts as Supervisor Software Interrupts.

hart_mask is a virtual address that points to a bit-vector of harts. The bit vector is represented as a sequence of unsigned longs whose length equals the number of harts in the system divided by the number of bits in an unsigned long, rounded up to the next integer.

This SBI call returns 0 upon success or an implementation specific negative error code.

Extension: Remote FENCE.I (EID #0x05)

long sbi_remote_fence_i(const unsigned long *hart_mask)

Instructs remote harts to execute FENCE.I instruction. The hart_mask is same as described in sbi_send_ipi().

This SBI call returns 0 upon success or an implementation specific negative error code.

Extension: Remote SFENCE.VMA (EID #0x06)

long sbi_remote_sfence_vma(const unsigned long *hart_mask,
                           unsigned long start,
                           unsigned long size)

Instructs the remote harts to execute one or more SFENCE.VMA instructions, covering the range of virtual addresses between start and start + size.

The remote fence operation applies to the entire address space if either:

  • start and size are both 0, or

  • size is equal to 2^XLEN-1.

This SBI call returns 0 upon success or an implementation specific negative error code.

Extension: Remote SFENCE.VMA with ASID (EID #0x07)

long sbi_remote_sfence_vma_asid(const unsigned long *hart_mask,
                                unsigned long start,
                                unsigned long size,
                                unsigned long asid)

Instruct the remote harts to execute one or more SFENCE.VMA instructions, covering the range of virtual addresses between start and start + size. This covers only the given ASID.

The remote fence operation applies to the entire address space if either:

  • start and size are both 0, or

  • size is equal to 2^XLEN-1.

This SBI call returns 0 upon success or an implementation specific negative error code.

Extension: System Shutdown (EID #0x08)

void sbi_shutdown(void)

Puts all the harts to shutdown state from supervisor point of view.

This SBI call doesn’t return irrespective whether it succeeds or fails.

Function Listing

Table 1. Legacy Function List
Function Name SBI Version FID EID Replacement EID

sbi_set_timer

0.1

0

0x00

0x54494D45

sbi_console_putchar

0.1

0

0x01

0x4442434E

sbi_console_getchar

0.1

0

0x02

0x4442434E

sbi_clear_ipi

0.1

0

0x03

N/A

sbi_send_ipi

0.1

0

0x04

0x735049

sbi_remote_fence_i

0.1

0

0x05

0x52464E43

sbi_remote_sfence_vma

0.1

0

0x06

0x52464E43

sbi_remote_sfence_vma_asid

0.1

0

0x07

0x52464E43

sbi_shutdown

0.1

0

0x08

0x53525354

RESERVED

0x09-0x0F