From efecbee7c0c265b0b2fe956f308e1a73cc63eda6 Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Mon, 3 Jun 2019 17:49:27 -0400
Subject: [PATCH] xx

---
 defs.h |  1 +
 uart.c | 10 +++++++---
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/defs.h b/defs.h
index 2a6c47a..1adbf78 100644
--- a/defs.h
+++ b/defs.h
@@ -174,6 +174,7 @@ void            usertrapret(void);
 void            uartinit(void);
 void            uartintr(void);
 void            uartputc(int);
+int             uartgetc(void);
 
 // vm.c
 void            kvminit(void);
diff --git a/uart.c b/uart.c
index 659c574..b6271c1 100644
--- a/uart.c
+++ b/uart.c
@@ -49,11 +49,15 @@ uartputc(int c)
   *R(0) = c;
 }
 
-uint
+int
 uartgetc(void)
 {
-  // XXX this isn't right, must check there's data in the FIFO.
-  return *R(0);
+  if(*(5) & 0x01){
+    // input data is ready.
+    return *R(0);
+  } else {
+    return -1;
+  };
 }
 
 void