| GPMC (General Purpose Memory Controller): |
| ========================================= |
| |
| GPMC is an unified memory controller dedicated to interfacing external |
| memory devices like |
| * Asynchronous SRAM like memories and application specific integrated |
| circuit devices. |
| * Asynchronous, synchronous, and page mode burst NOR flash devices |
| NAND flash |
| * Pseudo-SRAM devices |
| |
| GPMC is found on Texas Instruments SoC's (OMAP based) |
| IP details: http://www.ti.com/lit/pdf/spruh73 section 7.1 |
| |
| |
| GPMC generic timing calculation: |
| ================================ |
| |
| GPMC has certain timings that has to be programmed for proper |
| functioning of the peripheral, while peripheral has another set of |
| timings. To have peripheral work with gpmc, peripheral timings has to |
| be translated to the form gpmc can understand. The way it has to be |
| translated depends on the connected peripheral. Also there is a |
| dependency for certain gpmc timings on gpmc clock frequency. Hence a |
| generic timing routine was developed to achieve above requirements. |
| |
| Generic routine provides a generic method to calculate gpmc timings |
| from gpmc peripheral timings. struct gpmc_device_timings fields has to |
| be updated with timings from the datasheet of the peripheral that is |
| connected to gpmc. A few of the peripheral timings can be fed either |
| in time or in cycles, provision to handle this scenario has been |
| provided (refer struct gpmc_device_timings definition). It may so |
| happen that timing as specified by peripheral datasheet is not present |
| in timing structure, in this scenario, try to correlate peripheral |
| timing to the one available. If that doesn't work, try to add a new |
| field as required by peripheral, educate generic timing routine to |
| handle it, make sure that it does not break any of the existing. |
| Then there may be cases where peripheral datasheet doesn't mention |
| certain fields of struct gpmc_device_timings, zero those entries. |
| |
| Generic timing routine has been verified to work properly on |
| multiple onenand's and tusb6010 peripherals. |
| |
| A word of caution: generic timing routine has been developed based |
| on understanding of gpmc timings, peripheral timings, available |
| custom timing routines, a kind of reverse engineering without |
| most of the datasheets & hardware (to be exact none of those supported |
| in mainline having custom timing routine) and by simulation. |
| |
| gpmc timing dependency on peripheral timings: |
| [<gpmc_timing>: <peripheral timing1>, <peripheral timing2> ...] |
| |
| 1. common |
| cs_on: t_ceasu |
| adv_on: t_avdasu, t_ceavd |
| |
| 2. sync common |
| sync_clk: clk |
| page_burst_access: t_bacc |
| clk_activation: t_ces, t_avds |
| |
| 3. read async muxed |
| adv_rd_off: t_avdp_r |
| oe_on: t_oeasu, t_aavdh |
| access: t_iaa, t_oe, t_ce, t_aa |
| rd_cycle: t_rd_cycle, t_cez_r, t_oez |
| |
| 4. read async non-muxed |
| adv_rd_off: t_avdp_r |
| oe_on: t_oeasu |
| access: t_iaa, t_oe, t_ce, t_aa |
| rd_cycle: t_rd_cycle, t_cez_r, t_oez |
| |
| 5. read sync muxed |
| adv_rd_off: t_avdp_r, t_avdh |
| oe_on: t_oeasu, t_ach, cyc_aavdh_oe |
| access: t_iaa, cyc_iaa, cyc_oe |
| rd_cycle: t_cez_r, t_oez, t_ce_rdyz |
| |
| 6. read sync non-muxed |
| adv_rd_off: t_avdp_r |
| oe_on: t_oeasu |
| access: t_iaa, cyc_iaa, cyc_oe |
| rd_cycle: t_cez_r, t_oez, t_ce_rdyz |
| |
| 7. write async muxed |
| adv_wr_off: t_avdp_w |
| we_on, wr_data_mux_bus: t_weasu, t_aavdh, cyc_aavhd_we |
| we_off: t_wpl |
| cs_wr_off: t_wph |
| wr_cycle: t_cez_w, t_wr_cycle |
| |
| 8. write async non-muxed |
| adv_wr_off: t_avdp_w |
| we_on, wr_data_mux_bus: t_weasu |
| we_off: t_wpl |
| cs_wr_off: t_wph |
| wr_cycle: t_cez_w, t_wr_cycle |
| |
| 9. write sync muxed |
| adv_wr_off: t_avdp_w, t_avdh |
| we_on, wr_data_mux_bus: t_weasu, t_rdyo, t_aavdh, cyc_aavhd_we |
| we_off: t_wpl, cyc_wpl |
| cs_wr_off: t_wph |
| wr_cycle: t_cez_w, t_ce_rdyz |
| |
| 10. write sync non-muxed |
| adv_wr_off: t_avdp_w |
| we_on, wr_data_mux_bus: t_weasu, t_rdyo |
| we_off: t_wpl, cyc_wpl |
| cs_wr_off: t_wph |
| wr_cycle: t_cez_w, t_ce_rdyz |
| |
| |
| Note: Many of gpmc timings are dependent on other gpmc timings (a few |
| gpmc timings purely dependent on other gpmc timings, a reason that |
| some of the gpmc timings are missing above), and it will result in |
| indirect dependency of peripheral timings to gpmc timings other than |
| mentioned above, refer timing routine for more details. To know what |
| these peripheral timings correspond to, please see explanations in |
| struct gpmc_device_timings definition. And for gpmc timings refer |
| IP details (link above). |
