Put oven rack in middle position; preheat oven to 350 degrees F.
Have pineapple lengthwise, core and peel it. Cut pineapple crosswise into 1/4-inch thick wedges. Break two eggs into a small bowl. Sift together flour, baking powder, soda, salt, and spices into a bowl.
To prepare the topping: Use 1/4 cup margarine to grease a 9-inch round, 1.5 inch or 2 inch deep cake pan, lightly on the sides and generously on the bottom. Sprinkle all of the brown sugar evenly over the bottom of the pan. Sprinkle all of the pecans evenly over the brown sugar. Arrange the pineapple in a single layer over the nuts, starting in the center of the pan (in a decorative pattern if desired); overlap a second layer of pineapple.
To prepare the batter: Place 1/2 cup margarine, granulated sugar, and vanilla in mixing bowl. Beat together with an electric mixer at medium speed until light and fluffy (about 2 minutes). Add eggs one at a time, beating well after each addition. Reduce mixing speed to low and (beginning and ending with flour) alternately add flour mixture and buttermilk, in batches. Mix just until batter is smooth; don't over-mix.
Spread batter evenly over the pineapple; bake until a wooden toothpick inserted in the center of the cake comes out clean (about 40-45 minutes). Cool 5 minutes in pan, on a rack.
Invert a plate over cake pan and (keeping plate and pan firmly pressed together) invert cake onto plate. Remove the pan, and restore pineapple/caramel that stuck to the pan bottom (if any), putting it back onto the cake. Cool to room temperature.