dprintf: a generic debug-to-serial infrastructure

Actually provide real infrastructure for debug-to-serial.  Very
useful when debugging fullscreen applications, especially under an
emulator like Qemu.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 43 insertions, 0 deletions

diff --git a/com32/lib/vdprintf.c b/com32/lib/vdprintf.c
new file mode 100644
index 00000000..46a4b00d
--- /dev/null
+++ b/com32/lib/vdprintf.c
@@ -0,0 +1,43 @@
+/*
+ * vdprintf.c
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <stdarg.h>
+#include <unistd.h>
+#include <inttypes.h>
+#include <sys/io.h>
+
+#define BUFFER_SIZE	32768
+
+struct file_info;
+extern ssize_t __serial_write(struct file_info *, const void *, size_t);
+
+static const uint16_t debug_base = 0x03f8; /* I/O base address */
+
+int vdprintf(const char *format, va_list ap)
+{
+    int rv;
+    char buffer[BUFFER_SIZE];
+    char *p;
+
+    rv = vsnprintf(buffer, BUFFER_SIZE, format, ap);
+
+    if (rv < 0)
+	return rv;
+
+    if (rv > BUFFER_SIZE - 1)
+	rv = BUFFER_SIZE - 1;
+
+    /*
+     * This unconditionally outputs to a serial port at 0x3f8 regardless of
+     * if one is enabled or not (this means we don't have to enable the real
+     * serial console and therefore get conflicting output.)
+     */
+    while (rv--) {
+	while ((inb(debug_base+5) & 0x20) == 0)
+	    ;
+	outb(*p++, debug_base);
+    }
+}