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Documentation / bus-devices / ti-gpmc.txt




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Based on kernel version 3.13. Page generated on 2014-01-20 22:00 EST.

1	GPMC (General Purpose Memory Controller):
2	=========================================
3	
4	GPMC is an unified memory controller dedicated to interfacing external
5	memory devices like
6	 * Asynchronous SRAM like memories and application specific integrated
7	   circuit devices.
8	 * Asynchronous, synchronous, and page mode burst NOR flash devices
9	   NAND flash
10	 * Pseudo-SRAM devices
11	
12	GPMC is found on Texas Instruments SoC's (OMAP based)
13	IP details: http://www.ti.com/lit/pdf/spruh73 section 7.1
14	
15	
16	GPMC generic timing calculation:
17	================================
18	
19	GPMC has certain timings that has to be programmed for proper
20	functioning of the peripheral, while peripheral has another set of
21	timings. To have peripheral work with gpmc, peripheral timings has to
22	be translated to the form gpmc can understand. The way it has to be
23	translated depends on the connected peripheral. Also there is a
24	dependency for certain gpmc timings on gpmc clock frequency. Hence a
25	generic timing routine was developed to achieve above requirements.
26	
27	Generic routine provides a generic method to calculate gpmc timings
28	from gpmc peripheral timings. struct gpmc_device_timings fields has to
29	be updated with timings from the datasheet of the peripheral that is
30	connected to gpmc. A few of the peripheral timings can be fed either
31	in time or in cycles, provision to handle this scenario has been
32	provided (refer struct gpmc_device_timings definition). It may so
33	happen that timing as specified by peripheral datasheet is not present
34	in timing structure, in this scenario, try to correlate peripheral
35	timing to the one available. If that doesn't work, try to add a new
36	field as required by peripheral, educate generic timing routine to
37	handle it, make sure that it does not break any of the existing.
38	Then there may be cases where peripheral datasheet doesn't mention
39	certain fields of struct gpmc_device_timings, zero those entries.
40	
41	Generic timing routine has been verified to work properly on
42	multiple onenand's and tusb6010 peripherals.
43	
44	A word of caution: generic timing routine has been developed based
45	on understanding of gpmc timings, peripheral timings, available
46	custom timing routines, a kind of reverse engineering without
47	most of the datasheets & hardware (to be exact none of those supported
48	in mainline having custom timing routine) and by simulation.
49	
50	gpmc timing dependency on peripheral timings:
51	[<gpmc_timing>: <peripheral timing1>, <peripheral timing2> ...]
52	
53	1. common
54	cs_on: t_ceasu
55	adv_on: t_avdasu, t_ceavd
56	
57	2. sync common
58	sync_clk: clk
59	page_burst_access: t_bacc
60	clk_activation: t_ces, t_avds
61	
62	3. read async muxed
63	adv_rd_off: t_avdp_r
64	oe_on: t_oeasu, t_aavdh
65	access: t_iaa, t_oe, t_ce, t_aa
66	rd_cycle: t_rd_cycle, t_cez_r, t_oez
67	
68	4. read async non-muxed
69	adv_rd_off: t_avdp_r
70	oe_on: t_oeasu
71	access: t_iaa, t_oe, t_ce, t_aa
72	rd_cycle: t_rd_cycle, t_cez_r, t_oez
73	
74	5. read sync muxed
75	adv_rd_off: t_avdp_r, t_avdh
76	oe_on: t_oeasu, t_ach, cyc_aavdh_oe
77	access: t_iaa, cyc_iaa, cyc_oe
78	rd_cycle: t_cez_r, t_oez, t_ce_rdyz
79	
80	6. read sync non-muxed
81	adv_rd_off: t_avdp_r
82	oe_on: t_oeasu
83	access: t_iaa, cyc_iaa, cyc_oe
84	rd_cycle: t_cez_r, t_oez, t_ce_rdyz
85	
86	7. write async muxed
87	adv_wr_off: t_avdp_w
88	we_on, wr_data_mux_bus: t_weasu, t_aavdh, cyc_aavhd_we
89	we_off: t_wpl
90	cs_wr_off: t_wph
91	wr_cycle: t_cez_w, t_wr_cycle
92	
93	8. write async non-muxed
94	adv_wr_off: t_avdp_w
95	we_on, wr_data_mux_bus: t_weasu
96	we_off: t_wpl
97	cs_wr_off: t_wph
98	wr_cycle: t_cez_w, t_wr_cycle
99	
100	9. write sync muxed
101	adv_wr_off: t_avdp_w, t_avdh
102	we_on, wr_data_mux_bus: t_weasu, t_rdyo, t_aavdh, cyc_aavhd_we
103	we_off: t_wpl, cyc_wpl
104	cs_wr_off: t_wph
105	wr_cycle: t_cez_w, t_ce_rdyz
106	
107	10. write sync non-muxed
108	adv_wr_off: t_avdp_w
109	we_on, wr_data_mux_bus: t_weasu, t_rdyo
110	we_off: t_wpl, cyc_wpl
111	cs_wr_off: t_wph
112	wr_cycle: t_cez_w, t_ce_rdyz
113	
114	
115	Note: Many of gpmc timings are dependent on other gpmc timings (a few
116	gpmc timings purely dependent on other gpmc timings, a reason that
117	some of the gpmc timings are missing above), and it will result in
118	indirect dependency of peripheral timings to gpmc timings other than
119	mentioned above, refer timing routine for more details. To know what
120	these peripheral timings correspond to, please see explanations in
121	struct gpmc_device_timings definition. And for gpmc timings refer
122	IP details (link above).
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