In my timeline fleet of Viking ships reached South Africa in 10th century, and settled there. They defeated indigenous tribes and created a Viking kingdom. They also stopped the Bantu expansion in the 12th century, but they are unable to go further North due to their low tolerance of high heat and tropical parasites.
The Vikings were cut off from Europe since their arrival, but there is some trade with Arab, Indian and Chinese merchants similarly to Mapungubwe
What kind of technology should they have when the Portuguese arrive in 1488?