Hi
I need to configure a device tree (dts) for AM335x ( BeagleBone Black ) GPMC to access a 16 bits data, 1Mbytes SRAM ( Static RAM memory ), with NO multiplexed address with data. Where can I find information about device tree codification for this GPMC configuration?
Thank you
Sergio
Hi Sergio,
I am not aware of a TI example code for this specific use case.
However you can see what each of the parameters in the GPMC dts nodes is used for in Documentation/devicetree/bindings/memory-controller/omap-gpmc.txt (I am attaching the file here:
Device tree bindings for OMAP general purpose memory controllers (GPMC)
The actual devices are instantiated from the child nodes of a GPMC node.
Required properties:
- compatible: Should be set to one of the following:
ti,omap2420-gpmc (omap2420)
ti,omap2430-gpmc (omap2430)
ti,omap3430-gpmc (omap3430 & omap3630)
ti,omap4430-gpmc (omap4430 & omap4460 & omap543x)
ti,am3352-gpmc (am335x devices)
- reg: A resource specifier for the register space
(see the example below)
- ti,hwmods: Should be set to "ti,gpmc" until the DT transition is
completed.
- #address-cells: Must be set to 2 to allow memory address translation
- #size-cells: Must be set to 1 to allow CS address passing
- gpmc,num-cs: The maximum number of chip-select lines that controller
can support.
- gpmc,num-waitpins: The maximum number of wait pins that controller can
support.
- ranges: Must be set up to reflect the memory layout with four
integer values for each chip-select line in use:
<cs-number> 0 <physical address of mapping> <size>
Currently, calculated values derived from the contents
of the per-CS register GPMC_CONFIG7 (as set up by the
bootloader) are used for the physical address decoding.
As this will change in the future, filling correct
values here is a requirement.
GPMC DMA information.
- dmas GPMC dma channel
- dma-names Must be set to "rxtx"
Timing properties for child nodes. All are optional and default to 0.
- gpmc,sync-clk-ps: Minimum clock period for synchronous mode, in picoseconds
Chip-select signal timings (in nanoseconds) corresponding to GPMC_CONFIG2:
- gpmc,cs-on-ns: Assertion time
- gpmc,cs-rd-off-ns: Read deassertion time
- gpmc,cs-wr-off-ns: Write deassertion time
ADV signal timings (in nanoseconds) corresponding to GPMC_CONFIG3:
- gpmc,adv-on-ns: Assertion time
- gpmc,adv-rd-off-ns: Read deassertion time
- gpmc,adv-wr-off-ns: Write deassertion time
WE signals timings (in nanoseconds) corresponding to GPMC_CONFIG4:
- gpmc,we-on-ns Assertion time
- gpmc,we-off-ns: Deassertion time
OE signals timings (in nanoseconds) corresponding to GPMC_CONFIG4:
- gpmc,oe-on-ns: Assertion time
- gpmc,oe-off-ns: Deassertion time
Access time and cycle time timings (in nanoseconds) corresponding to
GPMC_CONFIG5:
- gpmc,page-burst-access-ns: Multiple access word delay
- gpmc,access-ns: Start-cycle to first data valid delay
- gpmc,rd-cycle-ns: Total read cycle time
- gpmc,wr-cycle-ns: Total write cycle time
- gpmc,bus-turnaround-ns: Turn-around time between successive accesses
- gpmc,cycle2cycle-delay-ns: Delay between chip-select pulses
- gpmc,clk-activation-ns: GPMC clock activation time
- gpmc,wait-monitoring-ns: Start of wait monitoring with regard to valid
data
Boolean timing parameters. If property is present parameter enabled and
disabled if omitted:
- gpmc,adv-extra-delay: ADV signal is delayed by half GPMC clock
- gpmc,cs-extra-delay: CS signal is delayed by half GPMC clock
- gpmc,cycle2cycle-diffcsen: Add "cycle2cycle-delay" between successive
accesses to a different CS
- gpmc,cycle2cycle-samecsen: Add "cycle2cycle-delay" between successive
accesses to the same CS
- gpmc,oe-extra-delay: OE signal is delayed by half GPMC clock
- gpmc,we-extra-delay: WE signal is delayed by half GPMC clock
- gpmc,time-para-granularity: Multiply all access times by 2
The following are only applicable to OMAP3+ and AM335x:
- gpmc,wr-access-ns: In synchronous write mode, for single or
burst accesses, defines the number of
GPMC_FCLK cycles from start access time
to the GPMC_CLK rising edge used by the
memory device for the first data capture.
- gpmc,wr-data-mux-bus-ns: In address-data multiplex mode, specifies
the time when the first data is driven on
the address-data bus.
GPMC chip-select settings properties for child nodes. All are optional.
- gpmc,burst-length Page/burst length. Must be 4, 8 or 16.
- gpmc,burst-wrap Enables wrap bursting
- gpmc,burst-read Enables read page/burst mode
- gpmc,burst-write Enables write page/burst mode
- gpmc,device-width Total width of device(s) connected to a GPMC
chip-select in bytes. The GPMC supports 8-bit
and 16-bit devices and so this property must be
1 or 2.
- gpmc,mux-add-data Address and data multiplexing configuration.
Valid values are 1 for address-address-data
multiplexing mode and 2 for address-data
multiplexing mode.
- gpmc,sync-read Enables synchronous read. Defaults to asynchronous
is this is not set.
- gpmc,sync-write Enables synchronous writes. Defaults to asynchronous
is this is not set.
- gpmc,wait-pin Wait-pin used by client. Must be less than
"gpmc,num-waitpins".
- gpmc,wait-on-read Enables wait monitoring on reads.
- gpmc,wait-on-write Enables wait monitoring on writes.
Example for an AM33xx board:
gpmc: gpmc@50000000 {
compatible = "ti,am3352-gpmc";
ti,hwmods = "gpmc";
reg = <0x50000000 0x2000>;
interrupts = <100>;
dmas = <&edma 52>;
dma-names = "rxtx";
gpmc,num-cs = <8>;
gpmc,num-waitpins = <2>;
#address-cells = <2>;
#size-cells = <1>;
ranges = <0 0 0x08000000 0x10000000>; /* CS0 @addr 0x8000000, size 0x10000000 */
/* child nodes go here */
};
You can use this example as a reference to create your custom dts node.
There is a gpmc-nor.txt & gpmc-nand.txt examples as well. They are located in Documentation/devicetree/bindings/mtd/
Also, if you search for GPMC in this forum, you will find plenty of discussions, which will be of use to you, like:
Hope this helps.
Best Regards,
Yordan
