1 files changed, 111 insertions, 0 deletions
diff --git a/drivers/cga.cc b/drivers/cga.cc
new file mode 100644
index 0000000..79facee
--- /dev/null
+++ b/drivers/cga.cc
@@ -0,0 +1,111 @@
+#include "cga.h"
+#include <string.h>
+
+static_assert(sizeof(CGA::Entry) == 2);
+
+/* cga registers, see https://www.lowlevel.eu/wiki/Color_Graphics_Adapter */
+constexpr uint8_t cursor_start = 10;   // 0xa
+constexpr uint8_t cursor_end = 11;     // 0xb
+constexpr uint8_t cursor_addr_h = 14;  // 0xe
+constexpr uint8_t cursor_addr_l = 15;  // 0xf
+
+/* cursor format
+ * register | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
+ *   start  |   | e | t |     scanline      |
+ *   end    |           |     scanline      |
+ * e = enable; t = timing
+ *  e t | effect
+ *  0 0 | no blinking
+ *  0 1 | hide cursor
+ *  1 0 | blink normally
+ *  1 1 | blink fast
+ */
+constexpr uint8_t cursor_hide = 0b00100000;
+
+CGA::CGA(Colour fg, Colour bg, uint32_t address) : colour_fg(fg), colour_bg(bg) {
+  buffer = reinterpret_cast<Entry*>(address);
+
+  // clear buffer
+  for (size_t y = 0; y < max_rows; y++) {
+    for (size_t x = 0; x < max_columns; x++) {
+      const size_t index = y * max_columns + x;
+      buffer[index].c = ' ';
+      buffer[index].fg = colour_fg;
+      buffer[index].bg = colour_bg;
+    }
+  }
+
+  enable_cursor(14, 15);
+  update_cursor();
+}
+
+void CGA::set_colour(Colour fg, Colour bg) {
+  colour_fg = fg;
+  colour_bg = bg;
+  for (size_t y = 0; y < max_rows; y++) {
+    for (size_t x = 0; x < max_columns; x++) {
+      const size_t index = y * max_columns + x;
+      buffer[index].fg = colour_fg;
+      buffer[index].bg = colour_bg;
+    }
+  }
+}
+
+void CGA::enable_cursor(uint8_t start, uint8_t end) {
+  p_idx.write(cursor_start);
+  p_dat.write((p_dat.read() & 0xc0) | start);
+
+  p_idx.write(cursor_end);
+  p_dat.write((p_dat.read() & 0xe0) | end);
+}
+void CGA::disable_cursor() {
+  p_idx.write(cursor_start);
+  p_dat.write(cursor_hide);
+}
+void CGA::update_cursor() {
+  const uint16_t pos = row * max_columns + column;
+
+  p_idx.write(cursor_addr_l);
+  p_dat.write(static_cast<uint8_t>(pos & 0xff));
+
+  p_idx.write(cursor_addr_h);
+  p_dat.write(static_cast<uint8_t>((pos >> 8) & 0xff));
+}
+
+void CGA::write(char c) {
+  switch (c) {
+    case '\n':
+      column = 0;
+      ++row;
+      break;
+    default: {
+      const size_t index = row * max_columns + column;
+      buffer[index].c = c;
+      ++column;
+    }
+  }
+
+  if (column == max_columns) {
+    column = 0;
+    ++row;
+  }
+
+  if (row == max_rows) {
+    // scroll up - move rows 1~25 up by one
+    for (size_t y = 1; y < max_rows; y++) {
+      const auto prev_y = y - 1;
+      for (size_t x = 0; x < max_columns; ++x) {
+        const auto prev = prev_y * max_columns + x;
+        const auto idx = y * max_columns + x;
+        buffer[prev] = buffer[idx];
+      }
+    }
+    --row;
+  }
+}
+
+void CGA::write(ViewIterator& iter) {
+  while (iter) {
+    write(iter.next());
+  }
+}