atmel,sam-smc

Vendor: Atmel Corporation

Description

Atmel Static Memory Controller (SMC).

The SMC allows to interface with static-memory mapped external devices such as
SRAM, PSRAM, PROM, EPROM, EEPROM, LCD Module, NOR Flash and NAND Flash.

The SMC is clocked through the Master Clock (MCK) which is controlled by the
Power Management Controller (PMC).

The SMC controller can have up to 4 children defining the connected external
memory devices. The reg property is set to the device's Chip Select.
Device Tree example taken from the sam4_xplained board:

&smc {
  status = "okay";
  pinctrl-0 = <&smc_default>;
  pinctrl-names = "default";

  is66wv51216dbll@0 {
    reg = <0>;

    atmel,smc-write-mode = "nwe";
    atmel,smc-read-mode = "nrd";
    atmel,smc-setup-timing = <1 1 1 1>;
    atmel,smc-pulse-timing = <6 6 6 6>;
    atmel,smc-cycle-timing = <7 7>;
  };
};

The above example configures a is66wv51216dbll-55 device. The device is a
low power static RAM which uses NWE and NRD signals connected to the WE
and OE inputs respectively. Assuming that MCK is 120MHz (cpu at full speed)
each MCK cycle will be equivalent to 8ns. Since the memory full cycle is
55ns, as per specification, it requires atmel,smc-cycle-timing of at least
7 pulses (56ns). The atmel,smc-cycle-timing is composed of three parts:
setup, pulse and hold. The setup is used to address the memory. The pulse
is the time used to read/write. The hold is used to release memory. For the
is66wv51216dbll-55 a minimum setup of 5ns (1 cycle) with at least 45ns
(6 cycles) for CPU read/write and no hold time is required.
Note: Since no hold parameter is available at SMC the atmel,smc-cycle-timing
should have additional cycles to accommodate for hold values.

  No Hold Time:
  cycle-timing (7) = setup (1) + pulse (6) + hold (0)

  With 3 Hold Times:
  cycle-timing (10) = setup (1) + pulse (6) + hold (3)

Finally, in order to make the memory available you will need to define new
memory device/s in DeviceTree:

sram1: sram@60000000 {
    compatible = "zephyr,memory-region", "mmio-sram";
    device_type = "memory";
    reg = <0x60000000 DT_SIZE_K(512)>;
    zephyr,memory-region = "SRAM1";
};

Properties

Top level properties

These property descriptions apply to “atmel,sam-smc” nodes themselves. This page also describes child node properties in the following sections.

Properties not inherited from the base binding file.

Name

Type

Details

pinctrl-0

phandles

 
Pin configuration/s for the first state. Content is specific to the
selected pin controller driver implementation.

pinctrl-1

phandles

 
Pin configuration/s for the second state. See pinctrl-0.

pinctrl-2

phandles

 
Pin configuration/s for the third state. See pinctrl-0.

pinctrl-3

phandles

 
Pin configuration/s for the fourth state. See pinctrl-0.

pinctrl-4

phandles

 
Pin configuration/s for the fifth state. See pinctrl-0.

pinctrl-names

string-array

 
Names for the provided states. The number of names needs to match the
number of states.

Child node properties

Name

Type

Details

reg

int

 
The device's SMC Chip Select number.
Valid range: 0 - 3

This property is required.

See Important properties for more information.

atmel,smc-write-mode

string

 
Select which signal is used for the write operation, either the chip
select (ncs) or a dedicated write enable pin (nwe). The data is put
on the bus during the pulse and hold steps of that signal.
The internal data buffers are switched to output mode after the NCS_WR
or NWE setup time.

This property is required.

Legal values: 'ncs', 'nwe'

atmel,smc-read-mode

string

 
Select which signal is used for the read operation, either the chip
select (ncs) or a dedicated output enable pin (nrd). The data is read
from the bus during the pulse and hold steps of that signal.

This property is required.

Legal values: 'ncs', 'nrd'

atmel,smc-setup-timing

array

 
This value is used to setup memory region (set address). The setup
values is an array of the signals NWE, NCS_WR, NRD and NCS_RD
where each value is configured in terms of MCK cycles. The SMC
controller allows use of setups value of 0 (no delays) when
consecutive reads/writes are used. Each value is encoded in
6 bits where the highest bit adds an offset of 128 cycles.
The effective value for each element is: 128 x setup[5] + setup[4:0]

This property is required.

atmel,smc-pulse-timing

array

 
This value is used to effectivelly read/write at memory region (pulse phase).
The pulse value is an array of the signals NWE, NCS_WR, NRD and NCS_RD where
each value is configured in terms of MCK cycles and a value of 0 is forbidden.
Each value is encoded in 7 bits where the highest bit adds an offset of 256
cycles. The effective value for each element is: 256 x setup[6] + setup[5:0]

This property is required.

atmel,smc-cycle-timing

array

 
SMC timing configurations in cycles for the total write and read
length respectively.
This value describes the entire write/read operation timing which
is defined as: cycle = setup + pulse + hold
Value has to be greater or equal to setup + pulse timing and
is encoded in 9 bits where the two highest bits are multiplied
with an offset of 256.
Effective value for each element: 256 x cycle[8:7] + cycle[6:0]

This property is required.