kfs: implemented the onscreen printing system

the function is prototyped this way:

int printk(const char *string);

the code has not been tested yet

Signed-off-by: Olivier Gayot <duskcoder@gmail.com>

1 files changed, 43 insertions, 0 deletions

diff --git a/kernel.c b/kernel.c
new file mode 100644
index 0000000..8e59664
--- /dev/null
+++ b/kernel.c
@@ -0,0 +1,43 @@
+#define NB_COLS 80
+#define NB_ROWS 25
+
+/* XXX doest not always handle memory overlaps */
+static void my_memmove(void *dest, const void *src, size_t n)
+{
+    for (size_t i = 0; i < n; ++i) {
+        dest[i] = src[i];
+    }
+}
+
+static void my_memset(void *dest, int c, size_t n)
+{
+    for (size_t i = 0; i < n; ++i) {
+        dest[i] = c;
+    }
+}
+
+int printk(const char *str)
+{
+    static char *offset = (char *) 0xb8000;
+    static char *addr = offset;
+    int count = 0;
+
+    for (int i = 0; str[i]; ++i) {
+        if ((long)addr >= 0xb8000 + NB_COLS * NB_ROWS) {
+            /* shift up */
+            addr -= NB_COLS;
+            my_memmove(offset, offset + NB_COLS, NB_COLS * (NB_ROWS - 1));
+            my_memset(offset + NB_COLS * (NB_ROWS - 1), ' ', NB_ROWS);
+        }
+
+        *addr++ = str[i]
+        ++count;
+
+    }
+
+    return count;
+}
+
+int main(void)
+{
+}