Save five instructions on underflow handling.
By using an optimized trap entry we can move instructions from
the window underflow function into the trap entry vector. By
setting WIM=0 and using RESTORE it is possible to move the
new WIM register content from the trapped window into the
to-be-restored register window. It is then possible to avoid
the WIM write delay.
---
c/src/lib/libbsp/sparc/shared/start/start.S | 11 ++++++++++-
c/src/lib/libcpu/sparc/reg_win/window.S | 14 ++++++--------
2 files changed, 16 insertions(+), 9 deletions(-)
diff --git a/c/src/lib/libbsp/sparc/shared/start/start.S
b/c/src/lib/libbsp/sparc/shared/start/start.S
index b7067b3..3e0e42e 100644
--- a/c/src/lib/libbsp/sparc/shared/start/start.S
+++ b/c/src/lib/libbsp/sparc/shared/start/start.S
@@ -51,6 +51,15 @@
nop
/*
+ * Window Underflow optimized trap table entry
+ */
+#define WUTRAP(_vector, _handler) \
+ mov %wim, %l3 ; \
+ sethi %hi(_handler), %l4 ; \
+ jmp %l4+%lo(_handler); \
+ mov %g0, %wim ! WIM = 0, so that we can restore regardless of WIM
+
+/*
* Software trap. Treat as BAD_TRAP for the time being...
*/
@@ -82,7 +91,7 @@ SYM(trap_table):
BAD_TRAP; ! 03 privileged instruction
BAD_TRAP; ! 04 fp disabled
WOTRAP(5, SYM(window_overflow_trap_handler)); ! 05 window overflow
- TRAP( 6, SYM(window_underflow_trap_handler) );! 06 window underflow
+ WUTRAP(6, SYM(window_underflow_trap_handler));! 06 window underflow
BAD_TRAP; ! 07 memory address not aligned
BAD_TRAP; ! 08 fp exception
BAD_TRAP; ! 09 data access exception
diff --git a/c/src/lib/libcpu/sparc/reg_win/window.S
b/c/src/lib/libcpu/sparc/reg_win/window.S
index 535dc83..9e4158e 100644
--- a/c/src/lib/libcpu/sparc/reg_win/window.S
+++ b/c/src/lib/libcpu/sparc/reg_win/window.S
@@ -73,9 +73,9 @@ SYM(window_overflow_trap_handler):
*
* On entry:
*
- * l0 = psr (from trap table)
* l1 = pc
* l2 = npc
+ * l3 = wim (from trap table)
*/
PUBLIC(window_underflow_trap_handler)
@@ -95,17 +95,15 @@ SYM(window_underflow_trap_handler):
* register will result in the local register set changing.
*/
- mov %wim, %l3 ! Calculate new WIM
+ ! In WIM 3 write instruction delay. since WIM<=0 from trap entry
sll %l3, 1, %l4 ! l4 = WIM << 1
srl %l3, SPARC_NUMBER_OF_REGISTER_WINDOWS-1, %l5
- ! l5 = WIM >> (Number Windows-1)
- or %l5, %l4, %l5 ! l5 = (WIM << 1) |
+ or %l5, %l4, %i5 ! %i5= (WIM << 1) |
! (WIM >> (Number Windows-1))
- mov %l5, %wim ! load the new WIM
- nop; nop; nop
restore ! Two restores to get into the
- restore ! window to restore
+ restore %o5, %g0, %l7 ! window to restore. Carry along new
WIM
ldd [%sp + 0x00], %l0 ! First the local register set
+ mov %l7, %wim ! load the new WIM
ldd [%sp + 0x08], %l2
ldd [%sp + 0x10], %l4
ldd [%sp + 0x18], %l6
@@ -116,7 +114,7 @@ SYM(window_underflow_trap_handler):
save ! Get back to the trap window.
save
jmp %l1 ! Re-execute restore.
- rett %l2
+ rett %l2
/*
* Flush All Windows trap handler.
--
1.7.0.4
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