[otbn,sw] Add simple program showcasing how to use the MAI

This simple program shows how to use the masking accelerator interface.

Signed-off-by: Pascal Etterli <[email protected]>

Author: etterli

sw/otbn/mai/mai_test.s

@@ -0,0 +1,78 @@
+/* Copyright lowRISC contributors (OpenTitan project). */
+/* Licensed under the Apache License, Version 2.0, see LICENSE for details. */
+/* SPDX-License-Identifier: Apache-2.0 */
+
+/**
+* Simple program to showcase how to use the MAI interface.
+*/
+
+.section .text.start
+main:
+  /* Load modulus */
+  li      x2,  0
+  la      x3,  mod32
+  bn.lid  x2,  0(x3)
+  bn.wsrw MOD, w0
+
+  /* Configure MAI - select B2A */
+  /* B2A requires the value 0x1 in the field operation. This field is in bits[2:1] */
+  li    x2, 0x2
+  csrrs x0, MAI_CTRL, x2
+  csrrs x3, MAI_STATUS, x0 /* Optional, just to populate the trace */
+
+  /* Write data into input WSRs */
+  bn.wsrw MAI_IN0_S0, w1
+  bn.wsrw MAI_IN0_S1, w2
+
+  /* Start conversion by writing the start bit */
+  li    x2, 0x1
+  csrrs x3, MAI_STATUS, x0  /* Optional, just to populate the trace */
+  csrrs x0, MAI_CTRL, x2
+  /* Read the status register to populate the trace to see when the state changes. */
+  csrrs x3, MAI_STATUS, x0
+  csrrs x3, MAI_STATUS, x0
+  csrrs x3, MAI_STATUS, x0
+  csrrs x3, MAI_STATUS, x0
+  csrrs x3, MAI_STATUS, x0
+  csrrs x3, MAI_STATUS, x0
+  csrrs x3, MAI_STATUS, x0
+  csrrs x3, MAI_STATUS, x0
+  csrrs x3, MAI_STATUS, x0
+  csrrs x3, MAI_STATUS, x0
+  csrrs x3, MAI_STATUS, x0
+  csrrs x3, MAI_STATUS, x0
+  csrrs x3, MAI_STATUS, x0
+  csrrs x3, MAI_STATUS, x0
+  csrrs x3, MAI_STATUS, x0
+  csrrs x3, MAI_STATUS, x0
+  csrrs x3, MAI_STATUS, x0
+  csrrs x3, MAI_STATUS, x0
+  csrrs x3, MAI_STATUS, x0
+  csrrs x3, MAI_STATUS, x0
+  csrrs x3, MAI_STATUS, x0
+  /* Poll busy bit - use this in production code */
+_poll_busy:
+  csrrs x2, MAI_STATUS, x0
+  andi  x2, x2, 0x1
+  bne   x2, x0, _poll_busy
+
+  /* Read results from output WSRs */
+  bn.wsrr w20, MAI_RES_S0
+  bn.wsrr w21, MAI_RES_S1
+
+  ecall
+
+.section .data
+
+/*
+  mod32 = 8380417
+*/
+mod32:
+  .word 0x007fe001
+  .word 0x00000000
+  .word 0x00000000
+  .word 0x00000000
+  .word 0x00000000
+  .word 0x00000000
+  .word 0x00000000
+  .word 0x00000000