Note 5 - Share-based Compensation - Stock Options (Details) - USD ($)		9 Months Ended
		Sep. 30, 2022	Sep. 30, 2021
2018 Equity Incentive Plan [Member]
Options outstanding, balance (in shares)		23,186,142	18,865,525
Exercise price per share, balance (in dollars per share)		$ 0.43	$ 0.40
Options granted (in shares)		4,748,212	3,686,462
Exercise price per share, granted (in dollars per share)		$ 0.27	$ 0.23
Options outstanding, balance (in shares)		27,934,354	22,591,987
Exercise price per share, balance (in dollars per share)		$ 0.43	$ 0.43
Options Non-vested (in shares)		(4,449,874)
Exercise price per share, Non-vested (in dollars per share)		$ 0.40
Options Vested (in shares)		23,484,480
Exercise price per share, Vested (in dollars per share)		$ 0.43
Vested, September 30, 2022 (in dollars per share)	[1]	1,893,000
2018 Equity Incentive Plan [Member] | Minimum [Member]
Exercise price per share, balance (in dollars per share)		0.12	0.16
Exercise price per share, granted (in dollars per share)		0.18	0.13
Exercise price per share, balance (in dollars per share)		0.12	0.12
Exercise price per share, Non-vested (in dollars per share)		0.12
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)		0.19	0.19
Exercise price per share, granted (in dollars per share)		0.22	0.19
Exercise price per share, balance (in dollars per share)		0.19	$ 0.19
Exercise price per share, Non-vested (in dollars per share)		0.22
Exercise price per share, Vested (in dollars per share)		$ 0.19
The 2007 Equity Incentive Plan [Member]
Options outstanding, balance (in shares)		2,879,246	5,689,363
Options outstanding, balance (in shares)		1,904,085	3,920,355
Weighted average exercise price per share, balance (in dollars per share)		$ 0.49	$ 0.44
Options outstanding, Expired (in shares)		(975,161)	(1,769,008)
Weighted average exercise price per share, Expired (in dollars per share)		$ 0.36	$ 0.40
Weighted average exercise price per share, balance (in dollars per share)		0.56	0.45
The 2007 Equity Incentive Plan [Member] | Minimum [Member]
Weighted average exercise price per share, balance (in dollars per share)		0.28	0.28
Weighted average exercise price per share, Expired (in dollars per share)		0.28	0.39
Weighted average exercise price per share, balance (in dollars per share)		0.28	0.28
The 2007 Equity Incentive Plan [Member] | Maximum [Member]
Weighted average exercise price per share, balance (in dollars per share)		0.94	0.94
Weighted average exercise price per share, Expired (in dollars per share)		0.35	0.51
Weighted average exercise price per share, balance (in dollars per share)		$ 0.94	$ 1.65
Non Plan [Member]
Options outstanding, balance (in shares)		20,119,207	20,749,583
Options granted (in shares)		105,797	43,956
Exercise price per share, granted (in dollars per share)			$ 0.23
Options outstanding, balance (in shares)		20,225,004	19,993,539
Options Non-vested (in shares)		(1,050,000)
Options Vested (in shares)		19,175,004
Vested, September 30, 2022 (in dollars per share)		$ 0.38
Weighted average exercise price per share, balance (in dollars per share)		0.41	$ 0.41
Options outstanding, Expired (in shares)			(800,000)
Weighted average exercise price per share, Expired (in dollars per share)			$ 1.00
Weighted average exercise price per share, balance (in dollars per share)		0.39	0.39
Weighted average exercise price per share, granted (in dollars per share)		0.26	0.23
Weighted average exercise price per share, Non-vested (in dollars per share)		$ 0.45
Vested, aggregate intrinsic value	[1]	$ 274,000
Exercise price per share, Expired (in dollars per share)			1.00
Non Plan [Member] | Minimum [Member]
Exercise price per share, balance (in dollars per share)		$ 0.17	0.17
Exercise price per share, balance (in dollars per share)		0.17	0.17
Exercise price per share, Non-vested (in dollars per share)		0.17
Exercise price per share, Vested (in dollars per share)		0.17
Non Plan [Member] | Maximum [Member]
Exercise price per share, balance (in dollars per share)		1.00	1.00
Exercise price per share, granted (in dollars per share)		0.27
Exercise price per share, balance (in dollars per share)		1.00	$ 1.00
Exercise price per share, Non-vested (in dollars per share)		0.45
Exercise price per share, Vested (in dollars per share)		$ 1.00

[1] Aggregate intrinsic value based on closing common stock price of $0.27 at September 30, 2022.