Note 3 - Stock-based Compensation - Information Related to Stock Options (Details) - $ / shares	6 Months Ended
	Mar. 28, 2020	Dec. 28, 2019	Sep. 28, 2019
Number of shares (in shares)	230,500
Weighted-average remaining contractual life (Year)	4 years 120 days
Weighted average exercise price (in dollars per share)	$ 7.28	$ 7.28	$ 8.36
Exercisable number of shares (in shares)	157,400
Exercisable weighted-average exercise price (in dollars per share)	$ 9.10
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)	9 years 251 days
Weighted average exercise price (in dollars per share)	$ 1.87
Exercisable number of shares (in shares)
Exercisable weighted-average exercise price (in dollars per share)
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)	20,300
Weighted-average remaining contractual life (Year)	6 years 142 days
Weighted average exercise price (in dollars per share)	$ 2.69
Exercisable number of shares (in shares)	14,000
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)	9 years 10 days
Weighted average exercise price (in dollars per share)	$ 3.61
Exercisable number of shares (in shares)	8,400
Exercisable weighted-average exercise price (in dollars per share)	$ 3.64
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)	4 years 87 days
Weighted average exercise price (in dollars per share)	$ 4.34
Exercisable number of shares (in shares)	14,200
Exercisable weighted-average exercise price (in dollars per share)	$ 4.37
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)	4 years 219 days
Weighted average exercise price (in dollars per share)	$ 7.75
Exercisable number of shares (in shares)	23,700
Exercisable weighted-average exercise price (in dollars per share)	$ 8.10
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)	97,100
Weighted-average remaining contractual life (Year)	175 days
Weighted average exercise price (in dollars per share)	$ 11.43
Exercisable number of shares (in shares)	97,100
Exercisable weighted-average exercise price (in dollars per share)	$ 11.43