arch-x86: Plumb up more of the i8237 DMA controller.

The device still can't actually do any DMAing, but now it's interface is
plumbed up so that it should work as expected up to the point where it's
asked to DMA something. Then it will panic as before.

Change-Id: I06a163a9a963bf87405e24fc5ceebe14f186adfd
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/55248
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/dev/x86/i8237.cc

@@ -99,31 +99,52 @@ I8237::I8237(const Params &p) : BasicPioDevice(p, 16), latency(p.pio_latency),
     // Add the other registers individually.
     regs.addRegisters({
         statusCommandReg.
-            reader(readUnimpl("status register")).
-            writer(writeUnimpl("command register")),
+            reader([this](auto &reg) -> uint8_t { return statusVal; }).
+            writer([this](auto &reg, const uint8_t &value) {
+                        commandVal = value;
+                    }),
 
         requestReg.
-            writer(writeUnimpl("request register")),
+            writer(this, &I8237::setRequestBit),
 
         setMaskBitReg.
             writer(this, &I8237::setMaskBit),
 
         modeReg.
-            writer(writeUnimpl("mode register")),
+            writer([this](auto &reg, const uint8_t &value) {
+                        channels[bits(value, 1, 0)].mode = value;
+                    }),
 
         clearFlipFlopReg.
-            writer(writeUnimpl("clear LSB/MSB flip-flop register")),
+            writer([this](auto &reg, const uint8_t &value) {
+                        highByte = false;
+                    }),
 
         temporaryMasterClearReg.
-            reader(readUnimpl("temporary register")).
-            writer(writeUnimpl("master clear register")),
+            reader([this](auto &reg) ->uint8_t { return tempVal; }).
+            writer([this](auto &reg, const uint8_t &value) { reset(); }),
 
         clearMaskReg.
-            writer(writeUnimpl("clear mask register")),
+            writer([this](auto &reg, const uint8_t &value) { maskVal = 0x0; }),
 
         writeMaskReg.
-            writer(writeUnimpl("write all mask register bits"))
+            writer([this](auto &reg, const uint8_t &value) {
+                        maskVal = bits(value, 3, 0);
+                    })
     });
+
+    reset();
+}
+
+void
+I8237::reset()
+{
+    maskVal = 0xf;
+    requestVal = 0x0;
+    commandVal = 0x0;
+    statusVal = 0x0;
+    tempVal = 0x0;
+    highByte = false;
 }
 
 void
@@ -131,9 +152,17 @@ I8237::setMaskBit(Register &reg, const uint8_t &command)
 {
     uint8_t select = bits(command, 1, 0);
     uint8_t bitVal = bits(command, 2);
-    if (!bitVal)
-        panic("Turning on i8237 channels unimplemented.");
-    replaceBits(maskReg, select, bitVal);
+    panic_if(!bitVal, "Turning on i8237 channels unimplemented.");
+    replaceBits(maskVal, select, bitVal);
+}
+
+void
+I8237::setRequestBit(Register &reg, const uint8_t &command)
+{
+    uint8_t select = bits(command, 1, 0);
+    uint8_t bitVal = bits(command, 2);
+    panic_if(bitVal, "Requesting i8237 DMA transfers is unimplemented.");
+    replaceBits(requestVal, select, bitVal);
 }
 
 Tick
@@ -155,13 +184,13 @@ I8237::write(PacketPtr pkt)
 void
 I8237::serialize(CheckpointOut &cp) const
 {
-    SERIALIZE_SCALAR(maskReg);
+    paramOut(cp, "maskReg", maskVal);
 }
 
 void
 I8237::unserialize(CheckpointIn &cp)
 {
-    UNSERIALIZE_SCALAR(maskReg);
+    paramIn(cp, "maskReg", maskVal);
 }
 
 } // namespace X86ISA

src/dev/x86/i8237.hh

@@ -48,7 +48,13 @@ class I8237 : public BasicPioDevice
 
   protected:
     Tick latency;
-    uint8_t maskReg = 0;
+    uint8_t maskVal;
+    //XXX These should be serialized.
+    uint8_t requestVal;
+    uint8_t commandVal;
+    uint8_t statusVal;
+    uint8_t tempVal;
+    bool highByte;
 
     RegisterBankLE regs;
 
@@ -68,6 +74,9 @@ class I8237 : public BasicPioDevice
 
         int number;
 
+        //XXX These should be serialized.
+        uint8_t mode = 0x0;
+
         ChannelAddrReg addrReg;
         ChannelRemainingReg remainingReg;
 
@@ -92,7 +101,9 @@ class I8237 : public BasicPioDevice
     WriteOnlyReg clearMaskReg;
     WriteOnlyReg writeMaskReg;
 
+    void reset();
     void setMaskBit(Register &reg, const uint8_t &command);
+    void setRequestBit(Register &reg, const uint8_t &command);
 
   public:
     using Params = I8237Params;