Note 3 - Stock-based Compensation - Information Related to Stock Options (Details) - $ / shares	6 Months Ended
	Mar. 27, 2021	Dec. 26, 2020	Sep. 26, 2020
Number of shares (in shares)	154,400
Weighted-average remaining contractual life (Year)	6 years 65 days
Weighted average exercise price (in dollars per share)	$ 4.38	$ 4.38	$ 4.54
Exercisable number of shares (in shares)	89,100
Exercisable weighted-average exercise price (in dollars per share)	$ 5.28
Range 1 [Member]
Lower range limit (in dollars per share)	1.01
Upper range limit (in dollars per share)	$ 2
Number of shares (in shares)	20,000
Weighted-average remaining contractual life (Year)	8 years 255 days
Weighted average exercise price (in dollars per share)	$ 1.87
Exercisable number of shares (in shares)	4,000
Exercisable weighted-average exercise price (in dollars per share)	$ 1.87
Range 2 [Member]
Lower range limit (in dollars per share)	2.01
Upper range limit (in dollars per share)	$ 3
Number of shares (in shares)	34,300
Weighted-average remaining contractual life (Year)	6 years 332 days
Weighted average exercise price (in dollars per share)	$ 2.61
Exercisable number of shares (in shares)	18,200
Exercisable weighted-average exercise price (in dollars per share)	$ 2.72
Range 3 [Member]
Lower range limit (in dollars per share)	3.01
Upper range limit (in dollars per share)	$ 4
Number of shares (in shares)	46,500
Weighted-average remaining contractual life (Year)	8 years 14 days
Weighted average exercise price (in dollars per share)	$ 3.61
Exercisable number of shares (in shares)	17,700
Exercisable weighted-average exercise price (in dollars per share)	$ 3.63
Range 4 [Member]
Lower range limit (in dollars per share)	4.01
Upper range limit (in dollars per share)	$ 5
Number of shares (in shares)	16,600
Weighted-average remaining contractual life (Year)	3 years 87 days
Weighted average exercise price (in dollars per share)	$ 4.34
Exercisable number of shares (in shares)	16,400
Exercisable weighted-average exercise price (in dollars per share)	$ 4.33
Range 5 [Member]
Lower range limit (in dollars per share)	5.01
Upper range limit (in dollars per share)	$ 10
Number of shares (in shares)	30,000
Weighted-average remaining contractual life (Year)	3 years 222 days
Weighted average exercise price (in dollars per share)	$ 7.92
Exercisable number of shares (in shares)	25,800
Exercisable weighted-average exercise price (in dollars per share)	$ 8.03
Range 6 [Member]
Lower range limit (in dollars per share)	10.01
Upper range limit (in dollars per share)	$ 15
Number of shares (in shares)	7,000
Weighted-average remaining contractual life (Year)	1 year 36 days
Weighted average exercise price (in dollars per share)	$ 10.20
Exercisable number of shares (in shares)	7,000
Exercisable weighted-average exercise price (in dollars per share)	$ 10.20