Avoid a race condition with the last bytes of an S88 read

[model-railway-devices.git] / arducontrol / s88.c

diff --git a/arducontrol/s88.c b/arducontrol/s88.c
index bce0a2a090bc69ddea12eb0663962ee3cf32f900..bd53deb72f55e252e2c88db1ed609e42fa896bae 100644 (file)
--- a/arducontrol/s88.c
+++ b/arducontrol/s88.c
@@ -11,12 +11,12 @@
 #define DATA PIN7
 #define BIT(x) (1<<(x))
 
-volatile uint8_t s88_read_count = 0;
-uint8_t s88_read_bit = 0;
-volatile uint8_t s88_read_phase = 0;
-uint8_t s88_data = 0;
-RINGBUFFER(s88_buffer, 8);
-uint8_t s88_out_index = 0;
+static volatile uint8_t s88_read_count = 0;
+static uint8_t s88_read_bit = 0;
+static volatile uint8_t s88_read_phase = 0;
+static uint8_t s88_data = 0;
+static RINGBUFFER(s88_buffer, 8);
+static uint8_t s88_out_index = 0;
 
 void s88_init(void)
 {
@@ -28,15 +28,17 @@ void s88_init(void)
 
 void s88_check(void)
 {
+       /* Check remaining read count before ringbuffer fill.  If it is zero, no
+       more bytes are arriving in the buffer and the contents can be sent out. */
+       uint8_t rc = s88_read_count;
        uint8_t count = ringbuffer_fill(s88_buffer);
-       if(count>=4 || (count>0 && !s88_read_count))
+       if(count>=4 || (count>0 && !rc))
        {
                uint8_t reply[10];
-               uint8_t i;
 
                reply[0] = S88_DATA;
                reply[1] = s88_out_index;
-               for(i=0; i<count; ++i)
+               for(uint8_t i=0; i<count; ++i)
                        reply[2+i] = ringbuffer_pop(s88_buffer);
                interface_send(reply, 2+count);
                s88_out_index += count;