int __retval; \
                \
                __retval = ioctl(device_handle, PPSETMODE, &addr_mode); \
+               assert(__retval >= 0); \
                __retval = write(device_handle, &val, 1); \
+               assert(__retval >= 0); \
        } while (0)
 #define AMT_AR(val) \
        do { \
                int __retval; \
                \
                __retval = ioctl(device_handle, PPSETMODE, &addr_mode); \
+               assert(__retval >= 0); \
                __retval = read(device_handle, &val, 1); \
+               assert(__retval >= 0); \
        } while (0)
 
 static const int data_mode = IEEE1284_MODE_EPP | IEEE1284_DATA;
                int __retval; \
                \
                __retval = ioctl(device_handle, PPSETMODE, &data_mode); \
+               assert(__retval >= 0); \
                __retval = write(device_handle, &val, 1); \
+               assert(__retval >= 0); \
        } while (0)
 #define AMT_DR(val) \
        do { \
                int __retval; \
                \
                __retval = ioctl(device_handle, PPSETMODE, &data_mode); \
+               assert(__retval >= 0); \
                __retval = read(device_handle, &val, 1); \
+               assert(__retval >= 0); \
        } while (0)
 
 #else