From 0d9978228b9226d16ba8272a03dd7e6c9ad83b3d Mon Sep 17 00:00:00 2001
From: Ben Bridle <ben@derelict.engineering>
Date: Mon, 16 Dec 2024 14:52:54 +1300
Subject: Implement a toggleable keyboard on the lower screen

---
 arm9/source/types/circbuf.c | 20 ++++++++++++++++++++
 arm9/source/types/circbuf.h | 16 ++++++++++++++++
 2 files changed, 36 insertions(+)
 create mode 100644 arm9/source/types/circbuf.c
 create mode 100644 arm9/source/types/circbuf.h

(limited to 'arm9/source/types')

diff --git a/arm9/source/types/circbuf.c b/arm9/source/types/circbuf.c
new file mode 100644
index 0000000..532a5a0
--- /dev/null
+++ b/arm9/source/types/circbuf.c
@@ -0,0 +1,20 @@
+#include "circbuf.h"
+
+u8 cb_read_byte(CircBuf *buf) {
+    if (buf->front != buf->back) {
+        return buf->mem[buf->front++];
+    } else {
+        return 0;
+    }
+}
+
+void cb_write_byte(CircBuf *buf, u8 byte) {
+    if (((buf->back+1)&0xff) != buf->front) {
+        buf->mem[buf->back++] = byte;
+    }
+}
+
+void cb_clear(CircBuf *buf) {
+    buf->front = 0;
+    buf->back = 0;
+}
diff --git a/arm9/source/types/circbuf.h b/arm9/source/types/circbuf.h
new file mode 100644
index 0000000..305f8bf
--- /dev/null
+++ b/arm9/source/types/circbuf.h
@@ -0,0 +1,16 @@
+#include <nds.h>
+
+#ifndef CIRCBUF_H_
+    #define CIRCBUF_H_
+
+    typedef struct {
+        u8 mem[256];
+        u8 front;      // start of buffer, read from here until back
+        u8 back;       // end of buffer, write past here until front
+    } CircBuf;
+
+    u8 cb_read_byte(CircBuf *buf);
+    void cb_write_byte(CircBuf *buf, u8 byte);
+    void cb_clear(CircBuf *buf);
+
+#endif
-- 
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