sandbox: Improve sandbox serial port keyboard interface

Implements the tstc() interface for the serial driver.  Multiplexing
the console between the serial port and a keyboard uses a polling
method of checking if characters are available; this means that the
serial console must be non-blocking when attempting to read
characters.

Signed-off-by: Taylor Hutt <thutt@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>

1 files changed, 38 insertions, 6 deletions

diff --git a/drivers/serial/sandbox.c b/drivers/serial/sandbox.c
index cb19401df6..b73520ca94 100644
--- a/drivers/serial/sandbox.c
+++ b/drivers/serial/sandbox.c
@@ -30,6 +30,19 @@
 #include <serial.h>
 #include <linux/compiler.h>
 
+/*
+ *
+ *   serial_buf: A buffer that holds keyboard characters for the
+ *		 Sandbox U-boot.
+ *
+ * invariants:
+ *   serial_buf_write		 == serial_buf_read -> empty buffer
+ *   (serial_buf_write + 1) % 16 == serial_buf_read -> full buffer
+ */
+static char serial_buf[16];
+static unsigned int serial_buf_write;
+static unsigned int serial_buf_read;
+
 static int sandbox_serial_init(void)
 {
 	os_tty_raw(0);
@@ -50,18 +63,37 @@ static void sandbox_serial_puts(const char *str)
 	os_write(1, str, strlen(str));
 }
 
-static int sandbox_serial_getc(void)
+static unsigned int increment_buffer_index(unsigned int index)
+{
+	return (index + 1) % ARRAY_SIZE(serial_buf);
+}
+
+static int sandbox_serial_tstc(void)
 {
-	char buf;
+	const unsigned int next_index =
+		increment_buffer_index(serial_buf_write);
 	ssize_t count;
 
-	count = os_read(0, &buf, 1);
-	return count == 1 ? buf : 0;
+	os_usleep(100);
+	if (next_index == serial_buf_read)
+		return 1;	/* buffer full */
+
+	count = os_read_no_block(0, &serial_buf[serial_buf_write], 1);
+	if (count == 1)
+		serial_buf_write = next_index;
+	return serial_buf_write != serial_buf_read;
 }
 
-static int sandbox_serial_tstc(void)
+static int sandbox_serial_getc(void)
 {
-	return 0;
+	int result;
+
+	while (!sandbox_serial_tstc())
+		;	/* buffer empty */
+
+	result = serial_buf[serial_buf_read];
+	serial_buf_read = increment_buffer_index(serial_buf_read);
+	return result;
 }
 
 static struct serial_device sandbox_serial_drv = {