Note 8 - Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Net operating loss carryforwards	$ 19,230	$ 18,141
Research and development credit carryforwards	2,747	3,058
Stock-based compensation	382	449
Accrued expenses and reserves	58	137
Depreciation and amortization	0	38
Deferred revenue	107	253
Right of use liability	318	357
Other	7	23
Gross deferred tax assets	22,849	22,456
Less: valuation allowance	(22,544)	(22,121)
Net deferred tax assets	305	335
Depreciation and amortization	(16)	0
Right of use asset	(289)	(328)
Net deferred tax assets	0	7
Deferred tax assets, non-current	0	7
Deferred tax liability, non-current	$ 0	$ 0