Note 5 - Share-based Compensation - Stock Options (Details) - USD ($)		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021
2018 Equity Incentive Plan [Member]
Options outstanding, balance (in shares)		23,186,142	18,865,525
Balance (in dollars per share)		$ 0.19	$ 0.19
Options granted (in shares)		6,322,233	4,320,617
Granted (in dollars per share)		$ 0.22	$ 0.19
Options Exercised (in shares)		(290,243)
Exercised (in dollars per share)		$ 0.16
Options expired (in shares)		(733,583)
Expired (in dollars per share)		$ 0.33
Options outstanding, balance (in shares)		28,484,549	23,186,142
Balance (in dollars per share)		$ 0.19	$ 0.19
Options Non-vested (in shares)		(3,746,708)
Non-vested (in dollars per share)		$ 0.19
Options Vested (in shares)		24,737,841
Vested, December 31, 2022 (in dollars per share)		$ 0.19
Vested, December 31, 2022	[1]	$ 596,000
2018 Equity Incentive Plan [Member] | Minimum [Member]
Exercise price per share, balance (in dollars per share)		$ 0.12	0.12
Exercise price per share, granted (in dollars per share)		0.18	0.13
Exercise price per share, Exercised (in dollars per share)		0.13
Exercise price per share, Expired (in dollars per share)		0.12
Exercise price per share, balance (in dollars per share)		0.12	0.12
Exercise price per share, Non-vested (in dollars per share)		0.18
Exercise price per share, Vested (in dollars per share)		0.12
2018 Equity Incentive Plan [Member] | Maximum [Member]
Exercise price per share, balance (in dollars per share)		0.43	0.43
Exercise price per share, granted (in dollars per share)		0.27	0.23
Exercise price per share, Exercised (in dollars per share)		0.23
Exercise price per share, Expired (in dollars per share)		0.40
Exercise price per share, balance (in dollars per share)		0.43	$ 0.43
Exercise price per share, Non-vested (in dollars per share)		0.27
Exercise price per share, Vested (in dollars per share)		$ 0.43
The 2007 Equity Incentive Plan [Member]
Options outstanding, balance (in shares)		2,879,246	5,689,363
Balance (in dollars per share)		$ 0.49	$ 0.44
Options expired (in shares)		(975,161)	(2,810,117)
Expired (in dollars per share)		$ 0.36	$ 0.38
Options outstanding, balance (in shares)		1,904,085	2,879,246
Balance (in dollars per share)		$ 0.56	$ 0.49
The 2007 Equity Incentive Plan [Member] | Minimum [Member]
Balance (in dollars per share)		0.23	0.23
Expired (in dollars per share)		0.35	0.34
Balance (in dollars per share)		0.23	0.23
The 2007 Equity Incentive Plan [Member] | Maximum [Member]
Balance (in dollars per share)		0.94	0.94
Expired (in dollars per share)		0.40	0.51
Balance (in dollars per share)		$ 0.94	$ 0.94
Non Plan [Member]
Options outstanding, balance (in shares)		20,119,207	20,749,583
Balance (in dollars per share)			$ 0.41
Options granted (in shares)		571,358	169,624
Granted (in dollars per share)		$ 0.19
Options expired (in shares)		(1,666,736)	(800,000)
Expired (in dollars per share)		$ 0.31	$ 1.00
Options outstanding, balance (in shares)		19,023,829	20,119,207
Options Non-vested (in shares)		(507,500)
Non-vested (in dollars per share)		$ 0.45
Options Vested (in shares)		18,516,329
Vested, December 31, 2022 (in dollars per share)		$ 0.39
Vested, December 31, 2022		$ 77,000
Non Plan [Member] | Minimum [Member]
Exercise price per share, balance (in dollars per share)		$ 0.12	$ 0.12
Exercise price per share, granted (in dollars per share)		0.17	0.17
Exercise price per share, Expired (in dollars per share)		0.30	1.00
Exercise price per share, balance (in dollars per share)			0.12
Exercise price per share, Non-vested (in dollars per share)		0.45
Exercise price per share, Vested (in dollars per share)		0.12
Non Plan [Member] | Maximum [Member]
Exercise price per share, balance (in dollars per share)		0.83	1.00
Balance (in dollars per share)		0.39
Exercise price per share, granted (in dollars per share)		0.27	0.23
Exercise price per share, Expired (in dollars per share)		0.40
Exercise price per share, balance (in dollars per share)			0.83
Balance (in dollars per share)		0.39	$ 0.39
Exercise price per share, Vested (in dollars per share)		$ 0.83

[1] Aggregate intrinsic value based on closing common stock price of $0.20 at December 31, 2022.