Selected Quarterly Financial Data (Unaudited) - Quarterly Financial Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Jul. 31, 2012	Apr. 28, 2012	Jan. 28, 2012	Oct. 29, 2011	Jul. 31, 2011	Apr. 30, 2011	Jan. 29, 2011	Oct. 30, 2010	Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2010
Condensed Financial Statements, Captions [Line Items]
Revenue	$ 16,799	$ 11,922	$ 13,184	$ 15,380	$ 12,959	$ 11,863	$ 12,157	$ 11,709	$ 57,285	$ 48,688	$ 68,617
Cost of revenue	7,179	5,455	5,435	6,262	5,627	4,881	5,117	6,885	24,331	22,510	30,954
Gross profit	9,620	6,467	7,749	9,118	7,332	6,982	7,040	4,824	32,954	26,178	37,663
Operating expenses:
Research and development	6,470	7,187	7,048	6,485	6,635	6,434	6,239	7,311	27,190	26,619	31,685
Sales and marketing	2,752	2,465	2,557	2,670	2,614	2,898	2,643	2,600	10,444	10,755	10,942
General and administrative	2,568	2,066	2,140	1,985	1,932	2,106	2,030	2,126	8,759	8,194	9,098
Asset Impairment	790								790		1,076
Restructuring				(271)					(271)		5,625
Total operating expenses	12,580	11,718	11,745	10,869	11,181	11,438	10,912	12,037	46,912	45,568	58,426
Loss from operations	(2,960)	(5,251)	(3,996)	(1,751)	(3,849)	(4,456)	(3,872)	(7,213)	(13,958)	(19,390)	(20,763)
Interest and other income, net	233	240	391	234	312	400	470	768	1,098	1,950	5,592
Loss before income taxes	(2,727)	(5,011)	(3,605)	(1,517)	(3,537)	(4,056)	(3,402)	(6,445)	(12,860)	(17,440)	(15,171)
Income tax expense	(202)	80	89	97	81	80	103	94	64	358	(366)
Net loss	$ (2,525)	$ (5,091)	$ (3,694)	$ (1,614)	$ (3,618)	$ (4,136)	$ (3,505)	$ (6,539)	$ (12,924)	$ (17,798)	$ (14,805)
Basic and diluted net loss per share	$ (0.09)	$ (0.18)	$ (0.13)	$ (0.06)	$ (0.13)	$ (0.14)	$ (0.12)	$ (0.23)