fix PortInterfaceBase

* setting busy latch LOW on exception is not ok: this creates a
  combinatorial loop
* setting st_done permanently was a bug, it left st_done permanently HI
* setting st_done when an exception is raised was also a bug

diff --git a/src/soc/experiment/pimem.py b/src/soc/experiment/pimem.py
index bc1daee125871b18c5280863a440e1cf73c44e0e..d4e7b60c9b7356db71da53679db0a6e346aea360 100644 (file)
--- a/src/soc/experiment/pimem.py
+++ b/src/soc/experiment/pimem.py
@@ -235,11 +235,9 @@ class PortInterfaceBase(Elaboratable):
 
         # LD/ST requested activates "busy" (only if not already busy)
         with m.If(self.pi.is_ld_i | self.pi.is_st_i):
+            comb += busy_l.s.eq(~busy_delay)
             with m.If(self.pi.exc_o.happened):
-                comb += busy_l.s.eq(0)
                 sync += Display("fast exception")
-            with m.Else():
-                comb += busy_l.s.eq(~busy_delay)
 
         # if now in "LD" mode: wait for addr_ok, then send the address out
         # to memory, acknowledge address, and send out LD data
@@ -283,6 +281,7 @@ class PortInterfaceBase(Elaboratable):
             comb += reset_l.s.eq(ldok)     # reset mode after 1 cycle
 
         # for ST mode, when addr has been "ok'd", wait for incoming "ST ok"
+        sync += st_done.s.eq(0)     # store done trigger
         with m.If(st_active.q & pi.st.ok):
             # shift data up before storing.  lenexp *bit* version of mask is
             # passed straight through as byte-level "write-enable" lines.
@@ -291,7 +290,7 @@ class PortInterfaceBase(Elaboratable):
             # TODO: replace with link to LoadStoreUnitInterface.x_store_data
             # and also handle the ready/stall/busy protocol
             stok = self.set_wr_data(m, stdata, lenexp.lexp_o)
-            sync += st_done.s.eq(1)     # store done trigger
+            sync += st_done.s.eq(~self.pi.exc_o.happened) # store done trigger
         with m.If(st_done.q):
             comb += reset_l.s.eq(stok)   # reset mode after 1 cycle