Under the scenario you described the minimum punishment would be 20 years.
This is because Robbery I is a class A felony punishable by a sentence of 10 years to life. However, there is an enhancement due to the use of a firearm, making the minimum sentence 20 years and the maximum punishment life in prison.
Traditionally, Alabama law prohibited probation for anyone sentenced to more than 15 years. However, since the Soles decision there is the possibility for probation on a 20 year sentence, but not on any sentence over 20. It is extremely rare however. I am familiar with all Dothan judges and can help if needed.