Add the wait state to the state machine

The implementation of the WAIT state currently constantly reads from
memory at the WAIT-ed address, resuming when a nonzero value comes back.
It might be better to have specific support for that in an interrupt
controller type of hardware which would send notifications when the
appropriate address changed.

diff --git a/hardware/core.py b/hardware/core.py
index 7a2fdc180a7b051cb4cfee584cb45ef45524cf59..1e02cb4229b98a179de6cba1d9e173a6ccfbe47e 100644 (file)
--- a/hardware/core.py
+++ b/hardware/core.py
@@ -7,6 +7,7 @@ class CpuState(Enum):
     EXEC = 1
     EXEC2 = 2
     HALT = 3
+    WAIT = 4
 
 
 class Core(Elaboratable):
@@ -53,6 +54,20 @@ class Core(Elaboratable):
         with m.Elif(self.state == CpuState.EXEC2):
             m.d.sync += self.state.eq(CpuState.READ)
             self.execute2(m, self.inst, self.d_in)
+        with m.Elif(self.state == CpuState.WAIT):
+            # This should be changed to avoid reading from memory every cycle
+            # for power purposes. Instead in the wait state we should just
+            # leave the address line set and the output line high, and let an
+            # external interrupt controller send back a wake signal.
+            m.d.comb += self.addr.eq(Cat(self.it, self.data1))
+            m.d.comb += self.r_en.eq(True)
+            with m.If(self.d_in):
+                m.d.sync += self.state.eq(CpuState.READ)
+                m.d.comb += [
+                    self.r_en.eq(False),
+                    self.w_en.eq(True),
+                    self.d_out.eq(self.d_in - 1),
+                ]
         return m
 
     def execute(self, m, inst):
@@ -63,12 +78,18 @@ class Core(Elaboratable):
             with m.Case("00000001"):  # NOPE
                 pass
             with m.Case("00000010"):  # PRNT
-                m.d.comb += self.debug.eq(self.it)
-                m.d.comb += self.debug_en.eq(True)
+                m.d.comb += [
+                    self.debug.eq(self.it),
+                    self.debug_en.eq(True),
+                ]
             with m.Case("00000011"):  # WAIT
-                pass  # @TODO: Implement WAIT
+                m.d.sync += self.state.eq(CpuState.WAIT)
+                m.d.comb += [
+                    self.addr.eq(Cat(self.it, self.data1),
+                    self.r_en.eq(True),
+                ]
             with m.Case("0000010-"):  # reserved
-                pass
+                m.d.sync += self.state.eq(CpuState.HALT)
             with m.Case("00000110"):  # CABA
                 pass  # @TODO: Implement CABA
             with m.Case("00000111"):  # COFA