[gem5-dev] Change in gem5/gem5[develop]: arch-x86: Implement count latching with the PIT read back command.

[Gabe Black (Gerrit) via gem5-dev]

Gabe Black has uploaded this change for review. (  
https://gem5-review.googlesource.com/c/public/gem5/+/55283 )

Change subject: arch-x86: Implement count latching with the PIT read back  
command.
......................................................................

arch-x86: Implement count latching with the PIT read back command.

This command can trigger count latching for any of the PIT channels
together with a single command, and can also latch a status byte. The
status byte is not implemented here, but there is already functionality
for latching the count which this can use.

Change-Id: Ic2ad7c73d0c521fdd6fe5f62cb478c6718f3b90c
---
M src/dev/intel_8254_timer.cc
M src/dev/intel_8254_timer.hh
2 files changed, 42 insertions(+), 4 deletions(-)



diff --git a/src/dev/intel_8254_timer.cc b/src/dev/intel_8254_timer.cc
index c0fc773..b9e37a1 100644
--- a/src/dev/intel_8254_timer.cc
+++ b/src/dev/intel_8254_timer.cc
@@ -58,12 +58,24 @@
 {
     int sel = data.sel;

-    if (sel == ReadBackCommand)
-       panic("PITimer Read-Back Command is not implemented.\n");
+    if (sel == ReadBackCommand) {
+        ReadBackCommandVal rb_val = static_cast<uint8_t>(data);

-    if (data.rw == LatchCommand)
+        panic_if(!rb_val.status,
+                "Latching the PIT status byte is not implemented.");
+
+        if (!rb_val.count) {
+            for (auto &cnt: counter) {
+                if (bits(rb_val.select, cnt->index()))
+                    cnt->latchCount();
+            }
+        }
+        return;
+    }
+
+    if (data.rw == LatchCommand) {
         counter[sel]->latchCount();
-    else {
+    } else {
         counter[sel]->setRW(data.rw);
         counter[sel]->setMode(data.mode);
         counter[sel]->setBCD(data.bcd);
diff --git a/src/dev/intel_8254_timer.hh b/src/dev/intel_8254_timer.hh
index 9876d13..e02a4cc 100644
--- a/src/dev/intel_8254_timer.hh
+++ b/src/dev/intel_8254_timer.hh
@@ -53,6 +53,16 @@
         Bitfield<0> bcd;
     EndBitUnion(CtrlReg)

+    BitUnion8(ReadBackCommandVal)
+        Bitfield<4> status; // Active low.
+        Bitfield<5> count; // Active low.
+        SubBitUnion(select, 3, 1)
+            Bitfield<3> cnt2;
+            Bitfield<2> cnt1;
+            Bitfield<1> cnt0;
+        EndSubBitUnion(select)
+    EndBitUnion(ReadBackCommandVal)
+
     enum SelectVal
     {
         SelectCounter0,
@@ -152,6 +162,8 @@
       public:
         Counter(Intel8254Timer *p, const std::string &name, unsigned int  
num);

+        unsigned int index() const { return num; }
+
         /** Latch the current count (if one is not already latched) */
         void latchCount();


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Gerrit-Project: public/gem5
Gerrit-Branch: develop
Gerrit-Change-Id: Ic2ad7c73d0c521fdd6fe5f62cb478c6718f3b90c
Gerrit-Change-Number: 55283
Gerrit-PatchSet: 1
Gerrit-Owner: Gabe Black <gabe.bl...@gmail.com>
Gerrit-MessageType: newchange
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