Hi, Oliver:
I found the function at file u8g_ll_api.c and the syntax are:
void u8g_SleepOn(u8g_t *u8g)
{
u8g_call_dev_fn(u8g, u8g->dev, U8G_DEV_MSG_SLEEP_ON, NULL);
}
void u8g_SleepOff(u8g_t *u8g)
{
u8g_call_dev_fn(u8g, u8g->dev, U8G_DEV_MSG_SLEEP_OFF, NULL);
}
In te reference we have SleepOn and SleepOff not u8g_SleepOn and u8g_SleepOff. Maybe this is the matter?
I'll try later at home and i'll say you something.