Note 3 - Stock-based Compensation - Summary of Stock Option Activity (Details) - Employee Stock Purchase Plan ESPP [Member] - $ / shares	12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2018
Balance, July 1, 2017 (in shares)	87,133	70,515	77,285
Balance, July 1, 2017 (in dollars per share)
Options granted (in shares)	86,946	55,227	63,607
Options granted, Weighted Average Exercise Price (in dollars per share)	$ 3.63	$ 5.45	$ 6.35
Shares Available for Grant, Options Granted (in shares)	(86,946)	(55,227)	(63,607)
Options exercised (in shares)	(20,615)	(11,981)	(17,561)
Options exercised, Weighted Average Exercise Price (in dollars per share)	$ 3.52	$ 5.72	$ 6.69
Options canceled (in shares)	(54,271)	(26,628)	(52,816)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period (in shares)	54,271	26,628	52,816
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)	86,946	55,227	63,607
Balance (in shares)	99,193	87,133	70,515
Balance , Weighted Average Exercise Price (in dollars per share)
Shares Available For Grant [Member]
Balance, July 1, 2017 (in shares)	412,867	450,007	365,581
Shares Available for Grant, Plan Expired (in shares)			(365,581)
Shares Available for Grant, Plan Authorized (in shares)			500,000
Options granted (in shares)	86,946	55,227	63,607
Shares Available for Grant, Options Granted (in shares)	(86,946)	(55,227)	(63,607)
Options canceled (in shares)	(54,271)	(18,087)	(13,614)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period (in shares)	54,271	18,087	13,614
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)	86,946	55,227	63,607
Shares Available for Grant (in shares)	380,192	412,867	450,007