Note 5 - Share-based Compensation - Stock Options (Details) - USD ($)		6 Months Ended
		Jun. 30, 2022	Jun. 30, 2021
2018 Equity Incentive Plan [Member]
Options outstanding, balance (in shares)		23,186,142	18,865,525
Weighted average exercise price per share, balance (in dollars per share)		$ 0.19	$ 0.19
Options granted (in shares)		3,782,923	2,483,691
Weighted average exercise price per share, granted (in dollars per share)		$ 0.22	$ 0.19
Options expired (in shares)		0
Weighted average exercise price per share, Expired (in dollars per share)		$ 0
Options outstanding, balance (in shares)		26,969,065	21,349,216
Options Non-vested (in shares)		(4,974,581)
Weighted average exercise price per share, Non-vested (in dollars per share)		$ 0.22
Options Vested (in shares)		21,994,484
Vested, June 30, 2022 (in dollars per share)		$ 0.19
Vested, aggregate intrinsic value	[1]	$ 378,000
Weighted average exercise price per share, balance (in dollars per share)		$ 0.19	$ 0.19
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, Non-vested (in dollars per share)		0.12
Exercise price per share, Vested (in dollars per share)		0.12
Exercise price per share, balance (in dollars per share)		0.12	0.12
2018 Equity Incentive Plan [Member] | Maximum [Member]
Exercise price per share, balance (in dollars per share)		0.43	0.40
Exercise price per share, granted (in dollars per share)		0.24	0.23
Exercise price per share, Non-vested (in dollars per share)		0.40
Exercise price per share, Vested (in dollars per share)		0.43
Exercise price per share, balance (in dollars per share)		$ 0.43	$ 0.43
The 2007 Equity Incentive Plan [Member]
Options outstanding, balance (in shares)		2,879,246	5,689,363
Weighted average exercise price per share, balance (in dollars per share)		$ 0.49	$ 0.44
Options expired (in shares)		(300,000)	(1,453,508)
Weighted average exercise price per share, Expired (in dollars per share)		$ 0.35	$ 0.40
Options outstanding, balance (in shares)		2,579,246	4,235,508
Weighted average exercise price per share, balance (in dollars per share)		$ 0.50	$ 0.45
The 2007 Equity Incentive Plan [Member] | Minimum [Member]
Weighted average exercise price per share, balance (in dollars per share)		0.23	0.23
Weighted average exercise price per share, Expired (in dollars per share)			0.39
Weighted average exercise price per share, balance (in dollars per share)		0.23	0.23
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)			0.51
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
Weighted average exercise price per share, balance (in dollars per share)		$ 0.41	$ 0.41
Options granted (in shares)		39,130	43,956
Exercise price per share, granted (in dollars per share)		$ 0.23
Weighted average exercise price per share, granted (in dollars per share)		$ 0.23	$ 0.23
Options outstanding, balance (in shares)		20,158,337	20,793,539
Options Non-vested (in shares)		(1,086,684)
Weighted average exercise price per share, Non-vested (in dollars per share)		$ 0.45
Options Vested (in shares)		19,071,653
Vested, June 30, 2022 (in dollars per share)		$ 0.41
Vested, aggregate intrinsic value	[1]	$ 44,000
Weighted average exercise price per share, balance (in dollars per share)		$ 0.41	$ 0.41
Non Plan [Member] | Minimum [Member]
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
Exercise price per share, balance (in dollars per share)		0.17	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)			0.23
Exercise price per share, Non-vested (in dollars per share)		0.45
Exercise price per share, Vested (in dollars per share)		1.00
Exercise price per share, balance (in dollars per share)		$ 1.00	$ 1.00

[1] Aggregate intrinsic value based on closing common stock price of $0.18 at June 30, 2022.