Based on kernel version 4.3. Page generated on 2015-11-02 12:44 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).