Factor out the dummy RoCC accelerator

4 files changed, 83 insertions, 0 deletions

diff --git a/dummy_rocc/dummy_rocc.ac b/dummy_rocc/dummy_rocc.ac
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/dummy_rocc/dummy_rocc.ac
diff --git a/dummy_rocc/dummy_rocc.cc b/dummy_rocc/dummy_rocc.cc
new file mode 100644
index 0000000..85ab7aa
--- /dev/null
+++ b/dummy_rocc/dummy_rocc.cc
@@ -0,0 +1,47 @@
+#include "rocc.h"
+#include "mmu.h"
+#include <cstring>
+
+class dummy_rocc_t : public rocc_t
+{
+ public:
+  const char* name() { return "dummy_rocc"; }
+
+  reg_t custom0(rocc_insn_t insn, reg_t xs1, reg_t xs2)
+  {
+    reg_t prev_acc = acc[insn.rs2];
+
+    if (insn.rs2 >= num_acc)
+      illegal_instruction();
+
+    switch (insn.funct)
+    {
+      case 0: // acc <- xs1
+        acc[insn.rs2] = xs1;
+        break;
+      case 1: // xd <- acc (the only real work is the return statement below)
+        break;
+      case 2: // acc[rs2] <- Mem[xs1]
+        acc[insn.rs2] = p->get_mmu()->load_uint64(xs1);
+        break;
+      case 3: // acc[rs2] <- accX + xs1
+        acc[insn.rs2] += xs1;
+        break;
+      default:
+        illegal_instruction();
+    }
+
+    return prev_acc; // in all cases, xd <- previous value of acc[rs2]
+  }
+
+  dummy_rocc_t()
+  {
+    memset(acc, 0, sizeof(acc));
+  }
+
+ private:
+  static const int num_acc = 4;
+  reg_t acc[num_acc];
+};
+
+REGISTER_EXTENSION(dummy_rocc, []() { return new dummy_rocc_t; })
diff --git a/dummy_rocc/dummy_rocc.mk.in b/dummy_rocc/dummy_rocc.mk.in
new file mode 100644
index 0000000..298b9f9
--- /dev/null
+++ b/dummy_rocc/dummy_rocc.mk.in
@@ -0,0 +1,7 @@
+dummy_rocc_subproject_deps = \
+	spike \
+	riscv \
+	softfloat \
+
+dummy_rocc_srcs = \
+	dummy_rocc.cc \
diff --git a/dummy_rocc/dummy_rocc_test.c b/dummy_rocc/dummy_rocc_test.c
new file mode 100644
index 0000000..94de8c0
--- /dev/null
+++ b/dummy_rocc/dummy_rocc_test.c
@@ -0,0 +1,29 @@
+// The following is a RISC-V program to test the functionality of the
+// dummy RoCC accelerator.
+// Compile with riscv64-unknown-elf-gcc dummy_rocc_test.c
+// Run with spike --extension=dummy_rocc pk a.out
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdint.h>
+
+int main() {
+  uint64_t x = 123, y = 456, z = 0;
+  // load x into accumulator 2 (funct=0)
+  asm volatile ("custom0 x0, %0, 2, 0" : : "r"(x));
+  // read it back into z (funct=1) to verify it
+  asm volatile ("custom0 %0, x0, 2, 1" : "=r"(z));
+  assert(z == x);
+  // accumulate 456 into it (funct=3)
+  asm volatile ("custom0 x0, %0, 2, 3" : : "r"(y));
+  // verify it
+  asm volatile ("custom0 %0, x0, 2, 1" : "=r"(z));
+  assert(z == x+y);
+  // do it all again, but initialize acc2 via memory this time (funct=2)
+  asm volatile ("custom0 x0, %0, 2, 2" : : "r"(&x));
+  asm volatile ("custom0 x0, %0, 2, 3" : : "r"(y));
+  asm volatile ("custom0 %0, x0, 2, 1" : "=r"(z));
+  assert(z == x+y);
+
+  printf("success!\n");
+}