io: add display unit

added rendering for modes 3,4,5
also changed how memory structuring works

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

include/io/dma.hh

@@ -0,0 +1,39 @@
+#include <bit>
+#include <cstdint>
+
+namespace matar {
+// NOLINTBEGIN(cppcoreguidelines-avoid-c-arrays)
+struct DmaControl {
+    struct {
+        int : 4; // this is supposed to be 5 bits, however, to align the struct
+                 // to 16 bits, we will adjust for the first LSB in the
+                 // read/write
+        uint8_t dst_adjustment : 2;
+        uint8_t src_adjustment : 2;
+        bool repeat : 1;
+        bool transfer_32 : 1;
+        int : 1;
+        uint8_t start_timing : 2;
+        bool irq_enable : 1;
+        bool enable : 1;
+    } value;
+
+    uint16_t read() const { return std::bit_cast<uint16_t>(value) << 1; };
+    void write(uint16_t raw) {
+        value = std::bit_cast<decltype(value)>(static_cast<uint16_t>(raw >> 1));
+    };
+};
+
+struct Dma {
+    using u16 = uint16_t;
+
+    struct {
+        u16 source[2];
+        u16 destination[2];
+        u16 word_count;
+        DmaControl control;
+    } channels[4];
+};
+// NOLINTEND(cppcoreguidelines-avoid-c-arrays)
+
+}