Allow updating the PC and SVSTATE registers while stopped

While the fetch address was overridden by a PC reset, the PC register
itself was updated (with NIA) only after the first instruction ended. Use
the time while the core is stopped to recognise and update the PC and
SVSTATE registers, before the first instruction starts.

diff --git a/src/soc/simple/issuer.py b/src/soc/simple/issuer.py
index 6ba8b39ddcb3bbb9950d0a1ded49d2ceefeb8c9a..f16eb8b50d7011202ec97e67a71a06739b394312 100644 (file)
--- a/src/soc/simple/issuer.py
+++ b/src/soc/simple/issuer.py
@@ -276,6 +276,15 @@ class TestIssuerInternal(Elaboratable):
                 with m.Else():
                     comb += core.core_stopped_i.eq(1)
                     comb += dbg.core_stopped_i.eq(1)
+                    # while stopped, allow updating the PC and SVSTATE
+                    with m.If(self.pc_i.ok):
+                        comb += self.state_w_pc.wen.eq(1 << StateRegs.PC)
+                        comb += self.state_w_pc.data_i.eq(self.pc_i.data)
+                        sync += pc_changed.eq(1)
+                    with m.If(self.svstate_i.ok):
+                        comb += new_svstate.eq(self.svstate_i.data)
+                        comb += update_svstate.eq(1)
+                        sync += sv_changed.eq(1)
 
             # go fetch the instruction at the current PC
             # at this point, there is no instruction running, that
@@ -350,6 +359,15 @@ class TestIssuerInternal(Elaboratable):
                 with m.Else():
                     comb += core.core_stopped_i.eq(1)
                     comb += dbg.core_stopped_i.eq(1)
+                    # while stopped, allow updating the PC and SVSTATE
+                    with m.If(self.pc_i.ok):
+                        comb += self.state_w_pc.wen.eq(1 << StateRegs.PC)
+                        comb += self.state_w_pc.data_i.eq(self.pc_i.data)
+                        sync += pc_changed.eq(1)
+                    with m.If(self.svstate_i.ok):
+                        comb += new_svstate.eq(self.svstate_i.data)
+                        comb += update_svstate.eq(1)
+                        sync += sv_changed.eq(1)
 
             # need to decode the instruction again, after updating SRCSTEP
             # in the previous state.