altos: Make stdio 8-bit clean by making pollchar return int

We were stealing one value (0xff) in the return value from pollchar to
indicate 'not ready yet'. Instead of doing that, use the integer value
-1 and have pollchar return an int instead of a char. That
necessitated cleaning a few other bits to make sure that 0xff wouldn't
get promoted to -1 on accident.

Signed-off-by: Keith Packard <keithp@keithp.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/src/core/ao.h b/src/core/ao.h
index 1aff3d49..54018b37 100644
--- a/src/core/ao.h
+++ b/src/core/ao.h
@@ -599,10 +599,10 @@ ao_monitor_init(void) __reentrant;
  * ao_stdio.c
  */
 
-#define AO_READ_AGAIN	((char) -1)
+#define AO_READ_AGAIN	(-1)
 
 struct ao_stdio {
-	char	(*pollchar)(void);
+	int	(*pollchar)(void);
 	void	(*putchar)(char c) __reentrant;
 	void	(*flush)(void);
 	uint8_t	echo;
@@ -621,7 +621,7 @@ uint8_t
 ao_echo(void);
 
 int8_t
-ao_add_stdio(char (*pollchar)(void),
+ao_add_stdio(int (*pollchar)(void),
 	     void (*putchar)(char) __reentrant,
 	     void (*flush)(void)) __reentrant;