Stock-based compensation expense included in the Company's consolidated financial statements for the three and six months ended June 28, 2020 and June 30, 2019 was as follows (in thousands):

	Three Months Ended				Six Months Ended
	June 28, 2020		June 30, 2019		June 28, 2020		June 30, 2019
Cost of revenue	$	31	$	18	$	43	$	44
Research and development		486		532		22		1,187
Selling, general and administrative		224		241		278		511
Total costs and expenses	$	741	$	791	$	343	$	1,742

During the six months ended June 28, 2020, the Company reversed stock-based compensation expense related to the cancellation of certain unvested performance based RSUs and restructuring related terminations. During the second quarter of 2020, the Company issued fully vested RSUs in lieu of cash for variable compensation to certain employees.

No stock options were granted during the three and six months ended June 28, 2020 and June 30, 2019.

The following table summarizes the activity in the shares available for grant under the 2019 Plan during the six months ended June 28, 2020 (in thousands):

	Shares Available for Grants
	2019 Plan
Balance at December 29, 2019		272
Authorized shares		550
RSUs granted		(289	)
PRSU's granted		(129	)
Options cancelled		49
RSUs forfeited or expired		163
PRSUs forfeited or expired		42
Balance at June 28, 2020		658

The following table summarizes stock options outstanding and stock option activity under the 2009 Plan and the 2019 Plan, and the related weighted average exercise price, for the six months ended June 28, 2020:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Term		Aggregate Intrinsic Value
	(in thousands)					(in years)		(in thousands)
Balance outstanding at December 29, 2019		185		$	32.09	3.32			—
Forfeited or expired		(48	)		—
Exercised		—			—
Balance outstanding at June 28, 2020		137		$	29.51		3.81	$	—
Exercisable at June 28, 2020		134		$	29.93		3.75	$	—
Vested and expected to vest at June 28, 2020		137		$	29.52		3.81	$	—

There was no intrinsic value for the stock options based on the Company’s closing stock price of $3.16 per share as of June 28, 2020, which would have been received by the option holders had all option holders exercised their options as of that date.

The total intrinsic value of options exercised during the six months ended June 28, 2020 and June 30, 2019 was $0. Total cash received from employees as a result of employee stock option exercises during the six months ended June 28, 2020 and June 30, 2019 was $0 and $3,600, respectively. The Company settles employee stock option exercises with newly issued common shares. In connection with these exercises, there was no tax benefit realized by the Company due to the Company's current loss position.

Total stock-based compensation related to stock options was approximately $14,000 and $24,000 for the three months ended June 28, 2020 and June 30, 2019, respectively, and $28,000 and $49,000 for the six months ended June 28, 2020 and June 30, 2018, respectively. As of June 28, 2020, the fair value of unvested stock options, net of forfeitures, was approximately $11,000. This unrecognized stock-based compensation expense is expected to be recorded over a weighted average period of 2.4 months.

The Company grants restricted stock units (“RSUs”) to employees and directors with various vesting terms. RSUs entitle the holder to receive, at no cost, one common share for each RSU as it vests. In general, the Company's policy is to withhold shares in settlement of employee tax withholding obligations upon the vesting of RSUs. The stock-based compensation related to RSUs was approximately $719,000 and $756,000 for the three months ended June 28, 2020 and June 30, 2019 and $306,000 and $1.6 million for the six months ended June 28, 2020 and June 30, 2019, respectively. Due to the cancellation of certain performance based RSUs and cancellations relating to restructuring, which was implemented in January 2020, the Company reversed stock-based compensation previously recorded resulting in a credit to the stock based compensation during the six months ended June 28, 2020. As of June 28, 2020 and June 30, 2019, there was approximately $1.7 million and $3.1 million, respectively, in unrecognized compensation expense related to RSUs. The remaining unrecognized stock-based compensation expense is expected to be recorded over a weighted average period of 1.0 year.

A summary of activity for the Company's RSUs for the six months ended June 28, 2020 is as follows:

	RSUs & PRSUs Outstanding
	Number of Shares			Weighted Average Grant Date Fair Value
	(in thousands)
Nonvested at December 29, 2019		377		$	12.55
Granted		418			4.50
Vested		(119	)		10.21
Forfeited		(205	)		—
Nonvested at June 28, 2020		471		$	7.99

As of June 28, 2020, 362,335 shares remained available for issuance under the 2009 ESPP. For the three months ended June 28, 2020 and June 30, 2019, the Company recorded stock-based compensation expense related to the 2009 ESPP of approximately $8,000 and $11,000, respectively. For the six months ended June 28, 2020 and June 30, 2019, the Company recorded stock-based compensation expense related to the 2009 ESPP of $8,000 and $60,000, respectively. The weighted average estimated fair value, as defined by the amended authoritative guidance, of rights issued pursuant to the Company's 2009 ESPP during the quarter ended June 28, 2020 and June 30, 2019, was $1.83 and $.0.31, respectively, per right, respectively.

The fair value of rights issued pursuant to the Company's 2009 ESPP was estimated on the commencement date of each offering period using the following weighted average assumptions:

	Three Months Ended						Six Months Ended
	June 28, 2020			June 30, 2019			June 28, 2020			June 30, 2019
Expected term (months)		6.08			6.00			6.08			6.00
Risk-free interest rate		0.15	%		2.40	%		0.15	%		2.40	%
Volatility		88.35	%		53.77	%		88.35	%		53.77	%
Dividend yield		—			—			—			—

As of June 28, 2020, there was $25,000 an unrecognized stock-based compensation expense relating to the Company's 2009 ESPP, which is expected to be recognized over a period of 4.7 months.