Handout

kernel/arch/cga.cc

@@ -0,0 +1,78 @@
+#include "cga.h"
+
+#include "../utils/math.h"
+#include "ioport.h"
+
+namespace CGA {
+// I/O Ports required for hardware cursor
+constexpr IOPort index_port(0x3d4);	 ///< Graphic card register selection
+constexpr IOPort data_port(0x3d5);	 ///< Read/Write selected register
+
+/*! \brief Helper structure for the hardware cursor
+ */
+union Cursor {
+	uint16_t value;
+	struct {
+		uint16_t low : 8;
+		uint16_t high : 6;
+		uint16_t : 2;
+	} __attribute__((packed));
+} __attribute__((packed));
+
+/*! \brief Register (for index_port)
+ */
+enum RegisterIndex {
+	CURSOR_START =
+		10,			  ///< Control the cursor (blink timing and start scanline)
+	CURSOR_END = 11,  ///< Control the cursors end scanline
+	START_ADDRESS_HIGH = 12,  ///< Base offset address for output (high)
+	START_ADDRESS_LOW = 13,	  ///< Base offset address for output (low)
+	CURSOR_HIGH = 14,		  ///< Cursor offset address (high)
+	CURSOR_LOW = 15,		  ///< Cursor offset address (low)
+};
+
+void setCursor(unsigned abs_x, unsigned abs_y) {
+	// Using the hardware cursor is quite important:
+	// The access to the IO Ports is rather slow and -- if interrupted by
+	// another output -- it will result in a strange word jumble.
+	// Hence this helps in a quite visible manner to understand the
+	// necessity of correct synchronization (and its performance impact).
+	if (abs_x < COLUMNS && abs_y < ROWS) {
+		Cursor pos = {static_cast<uint16_t>((abs_y * COLUMNS) + abs_x)};
+
+		// Select index 14 / CURSOR_HIGH register
+		index_port.outb(CURSOR_HIGH);
+		// Write high part of value to selected register (cursor high)
+		data_port.outb(pos.high);
+		// Select index 15 / CURSOR_LOW register
+		index_port.outb(CURSOR_LOW);
+		// Write low part of value to selected register (cursor low)
+		data_port.outb(pos.low);
+	}
+}
+
+void getCursor(unsigned& abs_x, unsigned& abs_y) {
+	Cursor pos = {.value = 0};
+
+	// Select index 14 / CURSOR_HIGH register
+	index_port.outb(CURSOR_HIGH);
+	// Read high part part of value from selected register (cursor high)
+	pos.high = data_port.inb();
+	// Select index 15 / CURSOR_LOW register
+	index_port.outb(CURSOR_LOW);
+	// Read low part of value from selected register (cursor low)
+	pos.low = data_port.inb();
+
+	// Calculate absolute position
+	abs_x = pos.value % COLUMNS;
+	abs_y = Math::min(pos.value / COLUMNS, ROWS - 1);
+}
+
+void show(unsigned abs_x, unsigned abs_y, char character, Attribute attrib) {
+	// Output only on current page
+	if (abs_x < COLUMNS && abs_y < ROWS) {
+		Cell cell(character, attrib);
+		TEXT_BUFFER_BASE[(abs_y * COLUMNS) + abs_x] = cell;
+	}
+}
+};	// namespace CGA