Add memory map functions

src/apple2.mem.c

@@ -0,0 +1,94 @@
+/*
+ * apple2.mem.c
+ */
+
+#include "apple2.h"
+
+/*
+ * Return a byte of memory from a bank-switchable address. This may be
+ * from ROM, from main memory, or from the "extra" 4k bank of RAM.
+ */
+vm_8bit
+apple2_mem_read_bank(vm_segment *segment, size_t address, void *_mach)
+{
+    apple2 *mach;
+
+    mach = (apple2 *)_mach;
+    
+    switch (mach->memory_mode) {
+        // Return memory from the rom bank
+        case MEMORY_BANK_ROM:
+            // We need to account for the difference in address location
+            // before we can successfully get any data from ROM.
+            return vm_segment_get(mach->rom, address - APPLE2_BANK_OFFSET);
+
+        // If the address is $D000..$DFFF, then we need to get the byte
+        // from the ram2 bank. Otherwise, we break to use default
+        // behavior.
+        case MEMORY_BANK_RAM2:
+            if (address < 0xE000) {
+                // The same caution holds for getting data from the
+                // second RAM bank.
+                return vm_segment_get(mach->ram2, 
+                                      address - APPLE2_BANK_OFFSET);
+            }
+            
+            break;
+
+        case MEMORY_BANK_RAM1:
+        default:
+            break;
+    }
+
+    // The "default" behavior as referred-to above is simply to return
+    // the value as held in our primary memory bank.
+    return segment->memory[address];
+}
+
+/*
+ * Write a byte into bank-switchable memory. Many of the same cautions,
+ * notes, etc. written for the read function apply here as well.
+ */
+void
+apple2_mem_write_bank(vm_segment *segment, 
+                      size_t address, vm_8bit value, void *_mach)
+{
+    apple2 *mach;
+
+    mach = (apple2 *)_mach;
+
+    switch (mach->memory_mode) {
+        case MEMORY_BANK_ROM:
+            vm_segment_set(mach->rom,
+                           address - APPLE2_BANK_OFFSET, value);
+            return;
+
+        case MEMORY_BANK_RAM2:
+            if (address < 0xE000) {
+                vm_segment_set(mach->ram2,
+                               address - APPLE2_BANK_OFFSET, value);
+                return;
+            }
+
+        case MEMORY_BANK_RAM1:
+        default:
+            break;
+    }
+
+    // Just set the value in main memory
+    segment->memory[address] = value;
+}
+
+/*
+ * Set the memory map functions for main memory in an apple2 machine
+ */
+void
+apple2_mem_map(apple2 *mach)
+{
+    size_t addr;
+
+    for (addr = APPLE2_BANK_OFFSET; addr < 0x10000; addr++) {
+        vm_segment_read_map(mach->memory, addr, apple2_mem_read_bank);
+        vm_segment_write_map(mach->memory, addr, apple2_mem_write_bank);
+    }
+}