[otbn] Specify memory accesses must be aligned
Fixes #2782
Signed-off-by: Greg Chadwick <gac@lowrisc.org>
diff --git a/hw/ip/otbn/data/insns.yml b/hw/ip/otbn/data/insns.yml
index db1d6ce..e5ca76e 100644
--- a/hw/ip/otbn/data/insns.yml
+++ b/hw/ip/otbn/data/insns.yml
@@ -727,6 +727,9 @@
funct3: b010
rd: grd
opcode: b00000
+ trailing-doc: |
+ Unaligned accesses are not supported.
+ Any unaligned access will result in an error.
- mnemonic: sw
rv32i: true
@@ -741,6 +744,9 @@
rs1: grs1
funct3: b010
opcode: b01000
+ trailing-doc: |
+ Unaligned accesses are not supported.
+ Any unaligned access will result in an error.
- mnemonic: beq
rv32i: true
@@ -1676,19 +1682,27 @@
- If `grs1_inc` is set, the value in `grs1` is incremented by the value WLEN/8 (one word).
- If `grd_inc` is set, the value in `grd` is incremented by the value 1.
+ Only aligned (to WLEN sized regions) accesses are supported.
+ Any unaligned access will result in an error.
+
TODO: how to handle overflows?
decode: |
rd = UInt(grd)
rs1 = UInt(grs1)
offset = UInt(offset)
operation: |
- memaddr = GPR[rs1] + (offset / WLEN / 8)
+ mem_addr = GPR[rs1] + offset
wdr_dest = GPR[rd]
- WDR[wdr_dest] = LoadWlenWordFromMemory(memaddr)
-
if grs1_inc and grd_inc:
- raise Unsupported() \# prevented in encoding
+ raise Unsupported() # prevented in encoding
+ if mem_addr % (WLEN / 8):
+ raise Unaligned()
+
+ mem_index = mem_addr // (WLEN / 8)
+
+ WDR[wdr_dest] = LoadWlenWordFromMemory(mem_index)
+
if grs1_inc:
GPR[rs1] = GPR[rs1] + (WLEN / 8)
if grd_inc:
@@ -1737,18 +1751,26 @@
- If `grs1_inc` is set, the value in `grs1` is incremented by the value WLEN/8 (one word).
- If `grs2_inc` is set, the value in `grs2` is incremented by the value 1.
+
+ Only aligned (to WLEN sized regions) accesses are supported.
+ Any unaligned access will result in an error.
decode: |
rs1 = UInt(grs1)
rs2 = UInt(grs2)
offset = UInt(offset)
operation: |
- memaddr = GPR[rs1] + offset / WLEN / 8
+ mem_addr = GPR[rs1] + offset
wdr_src = GPR[rs2]
- StoreWlenWordToMemory(memaddr, WDR[wdr_src])
-
if grs1_inc and grs2_inc:
raise Unsupported() # prevented in encoding
+ if mem_addr % (WLEN / 8):
+ raise Unaligned()
+
+ mem_index = mem_addr // (WLEN / 8)
+
+ StoreWlenWordToMemory(mem_index, WDR[wdr_src])
+
if grs1_inc:
GPR[rs1] = GPR[rs1] + (WLEN / 8)
if grs2_inc:
