Add functionality to set Write Allocate register.

Takes into account 15-16M hole too.

Provides "setWriteAllocateManual", a function to set manual range
+ Hole flag for later when we allow custom parameters.

Also provides "setWriteAllocateForSystemRAM", which finds
the total system memory size and sets write allocate for it.
It interprets the result of the Int15h call to find out if the 15-
16M hole needs to be respected.

The underlying assembly function called
"k6_setWriteAllocate" takes care of the
actual WHCR MSR.

K6.H

@@ -28,6 +28,8 @@ typedef struct {
 
 extern unsigned short k6_getMemorySize(unsigned long _far *memorySizeBelow16M, unsigned long _far *memorySizeAbove16M);
 
+extern void k6_setWriteAllocate(unsigned long value);
+
 extern void k6_getCPUIdentifier(char _far *cpuidString);
 extern cpuidProcessorType k6_getCPUProcessorType(void);
 
@@ -47,8 +49,14 @@ int checkSupportedCPU(void);
 
 int enableWriteCombiningForLFBs(void);
 
-// Memory stuff
+// Memory / Write Allocate stuff
 
 void showMemoryInfo(void);
 
+void setWriteAllocateManual(unsigned long writeAllocateMemorySize,
+                            int enableForMemoryHole);
+
+void setWriteAllocateForSystemRAM(void);
+
+
 #endif

K6CPU.ASM

@@ -7,6 +7,8 @@
 
 k6_getMemorySize        PROTO C memSizeBelow16M:FAR PTR DWORD, memSizeAbove16M:FAR PTR DWORD
 
+k6_setWriteAllocate        PROTO C whcrValue:DWORD
+
 k6_getCPUIdentifier     PROTO C cpuidString:FAR PTR CHAR
 k6_getCPUProcessorType  PROTO C
 
@@ -20,8 +22,8 @@ k6_getVBEModeInfo       PROTO C videoMode:WORD, vbeModeInfoPtr:FAR PTR BYTE
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ; getMemorySize
 ;
-; Parameters: pointer to DWORD to put the size below 16M in bytes in 
-;             pointer to DWORD to put the size above 16M in bytes in 
+; Parameters: pointer to DWORD to put the size below 16M in bytes in
+;             pointer to DWORD to put the size above 16M in bytes in
 ; Returns: 1 in ax on success, 0 if not.
 
 k6_getMemorySize PROC C uses ebx ecx edx es di,memSizeBelow16M:FAR PTR DWORD, memSizeAbove16M:FAR PTR DWORD
@@ -75,6 +77,44 @@ done:
 k6_getMemorySize ENDP
 
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+; setWriteAllocate
+;
+; Parameters: DWORD containing the register value.
+
+k6_setWriteAllocate PROC C USES eax ebx ecx edx, whcrValue:DWORD
+
+k6_MSR_WHCR        EQU 0C0000082h
+
+    ; MSR register ID needs to go in ecx
+
+    mov ecx, k6_MSR_WHCR ; Write Handling Control Register (WHCR)
+
+    ; 31-00 = eax
+    ; 63-32 = edx
+
+    ; we only write eax since that's what we need.
+
+    mov eax, whcrValue
+    xor edx, edx
+
+    ; since we're messing with caching stuff, we need to
+    ; write back and invalidate the cache first
+
+    pushf
+    cli
+    wbinvd
+
+    ; write the WHCR value
+
+    wrmsr
+    popf
+
+    ret
+
+
+k6_setWriteAllocate ENDP
+
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ; getCPUIdentifier
 ;

K6INIT.C

@@ -402,4 +402,55 @@ void showMemoryInfo(void)
 
     printf("\n");
 
+}
+
+void setWriteAllocateManual(unsigned long writeAllocateMemorySize,
+                            int enableForMemoryHole)
+{
+    // Sets write allocation for the given parameters
+    // The size is in bytes.
+
+    // 4 MiB mask: 0xFFC00000
+    // Memory hole bit: 0x00010000
+
+    // We need to increment this value by 1 or rather 0x0040000,
+    // else the last 4MB won't be inside the range!
+
+
+    unsigned long writeAllocateReg = (writeAllocateMemorySize + 1)
+                                      & 0xFFC00000UL;
+
+    if (enableForMemoryHole) {
+        writeAllocateReg = writeAllocateReg | 0x00010000UL;
+    }
+
+    printf("Enabling Write Allocate for 1 - %lu MiB\n",
+        writeAllocateReg >> 20UL);
+    printf("Setting Write Allocate WHCR Register: %08lx\n", writeAllocateReg);
+
+    k6_setWriteAllocate(writeAllocateReg);
+
+}
+
+void setWriteAllocateForSystemRAM(void)
+{
+    unsigned long writeAllocateMemorySize;
+    int systemHasMemoryHole;
+
+    writeAllocateMemorySize = getMemorySize();
+    systemHasMemoryHole = hasMemoryHole();
+
+    // Leave if we have an error in detection
+
+    if ((writeAllocateMemorySize == 0) || (systemHasMemoryHole < 0)) {
+        printf("ERROR getting memory info! Not setting Write allocate.\n");
+        return;
+    }
+
+    // Make sure to negate the memory hole var, since it needs to be 1 if
+    // we DON'T have a memory hole to enable write allocate for the 15-16M
+    // region!!
+
+    setWriteAllocateManual(writeAllocateMemorySize, !systemHasMemoryHole);
+
 }

MAIN.C

@@ -63,6 +63,8 @@ int main (int argc, char **argv)
         goto cleanup;
     }
 
+    setWriteAllocateForSystemRAM();
+
     /*  Parse the command line.  */
 
     signal(SIGINT, SIG_IGN);

README.MD

@@ -34,10 +34,14 @@ NO! I'm still learning.
   * yes
 * Set MTRR to enable Write combining for LFB
   * yes
-* Detect total available system memory and set WA mode
-  * No
-* Detect 15-16M Memory hole for WA
-  * No
+* Set Write Combine Mode
+  * no, need to do more research
+* Detect total available system memory 
+  * yes 
+* Detect 15-16M Memory hole 
+  * yes
+* Set write allocate for system memory
+  * yes (not verified yet, it's late)
 * Set K6-3 Multiplier
   * I don't actually own this CPU. ETA: When the cows come home