r.cost producing no data!

I'm trying to use r.cost (GRASS 4.1, update 1), and I must be doing
something obvious very wrong, because I'm getting nothing but 0s
in my output.

I've created a general cost surface for the region I'm working on
based on topographic features. I'm trying to create a cost surface
for travel from point A to point B on this surface. I'm using
the following command:

r.cost -v input=slope125 output=Eub.cost2 coordinate=797612,4211130 stop_coordinate=790915,4215562

where slope125 is my general cost surface, Eub.cost2 is a map that does
not exist yet, and the coordinate and stop_coordinate values are the
points I want to work with (from point and to point).

Can anyone help with this?

Neel Smith
nsmith@abacus.bates.edu