Note 5 - Share-based Compensation - Stock Options (Details) - $ / shares	6 Months Ended		12 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
2018 Equity Incentive Plan [Member]
Options outstanding, balance (in shares)	28,484,549	23,186,142	23,186,142
Weighted average exercise price per share, balance (in dollars per share)
Options granted (in shares)	2,636,712	3,782,923
Weighted average exercise price per share, granted (in dollars per share)
Options Unvested (in shares)	(4,121,892)
Weighted average exercise price per share, unvested (in dollars per share)
Options Vested (in shares)	26,999,369
Weighted average exercise price per share, vested (in dollars per share)	$ 402,000
Options outstanding, balance (in shares)	31,121,261	26,969,065	28,484,549
Weighted average exercise price per share, balance (in dollars per share)
2018 Equity Incentive Plan [Member] | Minimum [Member]
Exercise price per share, balance (in dollars per share)	0.12	0.16	0.16
Exercise price per share, granted (in dollars per share)	0.18	0.18
Exercise price per share, Unvested (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	0.12
2018 Equity Incentive Plan [Member] | Maximum [Member]
Exercise price per share, balance (in dollars per share)	0.43	0.43	0.43
Exercise price per share, granted (in dollars per share)	0.20	0.24
Exercise price per share, Unvested (in dollars per share)	0.32
Exercise price per share, Vested (in dollars per share)	0.43
Exercise price per share, balance (in dollars per share)	0.43	0.43	0.43
2018 Equity Incentive Plan [Member] | Weighted Average [Member]
Exercise price per share, balance (in dollars per share)	0.19	0.19	0.19
Exercise price per share, granted (in dollars per share)	0.19	0.22
Exercise price per share, Unvested (in dollars per share)	0.19
Exercise price per share, Vested (in dollars per share)	0.19
Exercise price per share, balance (in dollars per share)	$ 0.19	$ 0.19	$ 0.19
The 2007 Equity Incentive Plan [Member]
Options outstanding, balance (in shares)	1,904,085	2,879,246	2,879,246
Weighted average exercise price per share, balance (in dollars per share)	$ 0.56	$ 0.49	$ 0.49
Options outstanding, balance (in shares)	1,864,085	2,579,246	1,904,085
Weighted average exercise price per share, balance (in dollars per share)	$ 0.56	$ 0.49	$ 0.56
Options outstanding, Expired (in shares)	(40,000)	(300,000)
Weighted average exercise price per share, Expired (in dollars per share)	$ 0.28	$ 0.35
The 2007 Equity Incentive Plan [Member] | Minimum [Member]
Weighted average exercise price per share, balance (in dollars per share)	0.28	0.23	0.23
Weighted average exercise price per share, balance (in dollars per share)	0.28	0.23	0.28
The 2007 Equity Incentive Plan [Member] | Maximum [Member]
Weighted average exercise price per share, balance (in dollars per share)	0.69	0.94	0.94
Weighted average exercise price per share, balance (in dollars per share)	$ 0.69	$ 0.94	$ 0.69
Non Plan [Member]
Options outstanding, balance (in shares)	19,023,829	20,119,207	20,119,207
Options granted (in shares)	60,040	39,130
Exercise price per share, granted (in dollars per share)		$ 0.23
Options Unvested (in shares)	(507,500)
Exercise price per share, Unvested (in dollars per share)	$ 0.45
Options Vested (in shares)	18,576,369
Weighted average exercise price per share, vested (in dollars per share)	$ 46,000
Options outstanding, balance (in shares)	19,083,869	20,158,337	19,023,829
Non Plan [Member] | Minimum [Member]
Exercise price per share, balance (in dollars per share)	$ 0.12	$ 0.12	$ 0.12
Exercise price per share, granted (in dollars per share)	0.18
Exercise price per share, Vested (in dollars per share)	0.12
Exercise price per share, balance (in dollars per share)	0.12	0.12	0.12
Non Plan [Member] | Maximum [Member]
Exercise price per share, balance (in dollars per share)	0.83	0.83	0.83
Exercise price per share, granted (in dollars per share)	0.20
Exercise price per share, Vested (in dollars per share)	0.83
Exercise price per share, balance (in dollars per share)	0.83	0.83	0.83
Non Plan [Member] | Weighted Average [Member]
Exercise price per share, balance (in dollars per share)	0.39	0.39	0.39
Exercise price per share, granted (in dollars per share)	0.20	0.23
Exercise price per share, Vested (in dollars per share)	0.38
Exercise price per share, balance (in dollars per share)	$ 0.39	$ 0.39	$ 0.39