sprites!!!!!!

1 files changed, 53 insertions, 0 deletions

diff --git a/nes/controller.go b/nes/controller.go
new file mode 100644
index 0000000..51afe20
--- /dev/null
+++ b/nes/controller.go
@@ -0,0 +1,53 @@
+package nes
+
+// bit order matches the order the console reads them out in
+const (
+	ButtonA uint8 = 1 << iota
+	ButtonB
+	ButtonSelect
+	ButtonStart
+	ButtonUp
+	ButtonDown
+	ButtonLeft
+	ButtonRight
+)
+
+// standard controller, it is just an 8 bit shift register
+// https://www.nesdev.org/wiki/Standard_controller
+type controller struct {
+	buttons uint8 // what is held right now
+	shift   uint8 // what the cpu is reading out
+	strobe  bool
+}
+
+// while strobe is high the shift register keeps copying the buttons
+func (c *controller) setStrobe(on bool) {
+	c.strobe = on
+	if on {
+		c.shift = c.buttons
+	}
+}
+
+func (c *controller) setButtons(b uint8) {
+	c.buttons = b
+	if c.strobe {
+		c.shift = b
+	}
+}
+
+// returns one button per read, A first. with strobe high it stays on A
+func (c *controller) read() uint8 {
+	bit := c.shift & 1
+	if !c.strobe {
+		// ones get shifted in, so reads after the 8th return 1
+		c.shift = c.shift>>1 | 0x80
+	}
+	// upper bits are open bus, which is $40 here since that is the high byte
+	// of the address that was read
+	return 0x40 | bit
+}
+
+// port is 0 for controller 1 and 1 for controller 2
+func (n *Console) SetButtons(port int, buttons uint8) {
+	n.controllers[port].setButtons(buttons)
+}