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Enable vector unit without misa.V #430

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Enable vector unit without misa.V #430

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22 changes: 13 additions & 9 deletions gloss/crt0.S
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Original file line number Diff line number Diff line change
Expand Up @@ -252,16 +252,20 @@ _skip_init:
csrwi fcsr, 0
1:

/* Check for vector extension support and enable it if found.
* Omit if toolchain doesn't support the vector extension. */
#ifdef __riscv_v
csrr a5, misa
li a4, 0x200000
and a5, a5, a4
beqz a5, 1f
/* Check for vector extension support and enable the vector unit if found.
* Omit if the toolchain doesn't support any vector extension.
* (NB: __riscv_vector is defined for V as well as Zve*.) */
#ifdef __riscv_vector
/* Unfortunately, Zve* (embedded vector extensions) do not set misa.V,
* so, until the RISC-V standard discovery mechanism is finalized, we use
* a trick: we set mstatus.VS to Dirty, and then read it back. It's set to
* Off iff there's no vector unit. This should detect the presence of any
* standard vector extension (V or Zve*) or the absence of all. */
li a5, 0x600
csrs mstatus, a5
csrr a5, mstatus
ori a5, a5, 0x200
csrw mstatus, a5
andi a5, a5, 0x600
beqz a5, 1f
vsetivli x0, 0, e8, m1, ta, ma
csrwi vcsr, 0
1:
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