Begin implementing VDP

1 files changed, 64 insertions, 0 deletions

diff --git a/vdp.cpp b/vdp.cpp
new file mode 100644
index 0000000..632429d
--- /dev/null
+++ b/vdp.cpp
@@ -0,0 +1,64 @@
+/* SPDX-License-Identifier: Unlicense
+ */
+
+#include "vdp.hpp"
+
+uint32_t VDP::Read(const uint32_t offset, const enum bitness bitness)
+{
+    const uint32_t res{};
+    if (DEBUG_TRACE_VDP_ACCESS) {
+        printf(
+                "VDP r%d%s @0x%08x 0x%0*x\n",
+                bitness * 8,
+                (bitness <= 1 ? " " : ""),
+                base_address + offset,
+                bitness * 2,
+                res);
+    }
+    if (bitness == BITNESS_32) {
+        // TODO
+    } else if (bitness == BITNESS_16) {
+        // TODO
+    }
+    // Ignore 8-bit reads for now
+    return 0;
+}
+
+void VDP::Write(const uint32_t offset, const enum bitness bitness, const uint32_t value)
+{
+    if (DEBUG_TRACE_VDP_ACCESS) {
+        printf(
+                "VDP w%d%s @0x%08x 0x%0*x",
+                bitness * 8,
+                (bitness <= 1 ? " " : ""),
+                base_address + offset,
+                bitness * 2,
+                value);
+    }
+    if (bitness == BITNESS_32) {
+        if (offset == 4 || offset == 6) {
+            writeControl((value >> 16) & 0xffff);
+            writeControl(value & 0xffff);
+        }
+    } else if (bitness == BITNESS_16) {
+        if (offset == 4 || offset == 6) {
+            writeControl(value & 0xffff);
+        }
+    }
+    if (DEBUG_TRACE_VDP_ACCESS) {
+        printf("\n");
+    }
+    // Ignore 8-bit writes for now
+}
+
+void VDP::writeControl(const uint16_t value)
+{
+    if (((value >> 13) & 0x7) == 4) {
+        const uint8_t reg_num = (value >> 8) & 0x1f;
+        const uint8_t reg_val = value & 0xff;
+        if (DEBUG_TRACE_VDP_ACCESS) {
+            printf(": reg 0x%02x w 0x%02x", reg_num, reg_val);
+        }
+        _reg[reg_num] = reg_val;
+    }
+}