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SPI/QSPI Dual flash connection modes:
=====================================
This describes how SPI/QSPI flash memories are connected to a given
controller in a single chip select line.
Current spi_flash framework supports, single flash memory connected
to a given controller with single chip select line, but there are some
hw logics(ex: xilinx zynq qspi) that describes two/dual memories are
connected with a single chip select line from a controller.
"dual_flash" from include/spi.h describes these types of connection mode
Possible connections:
--------------------
SF_SINGLE_FLASH:
- single spi flash memory connected with single chip select line.
+------------+ CS +---------------+
| |----------------------->| |
| Controller | I0[3:0] | Flash memory |
| SPI/QSPI |<======================>| (SPI/QSPI) |
| | CLK | |
| |----------------------->| |
+------------+ +---------------+
SF_DUAL_STACKED_FLASH:
- dual spi/qspi flash memories are connected with a single chipselect
line and these two memories are operating stacked fasion with shared buses.
- xilinx zynq qspi controller has implemented this feature [1]
+------------+ CS +---------------+
| |---------------------->| |
| | I0[3:0] | Upper Flash |
| | +=========>| memory |
| | | CLK | (SPI/QSPI) |
| | | +---->| |
| Controller | CS | | +---------------+
| SPI/QSPI |------------|----|---->| |
| | I0[3:0] | | | Lower Flash |
| |<===========+====|====>| memory |
| | CLK | | (SPI/QSPI) |
| |-----------------+---->| |
+------------+ +---------------+
- two memory flash devices should has same hw part attributes (like size,
vendor..etc)
- Configurations:
on LQSPI_CFG register, Enable TWO_MEM[BIT:30] on LQSPI_CFG
Enable U_PAGE[BIT:28] if U_PAGE flag set - upper memory
Disable U_PAGE[BIT:28] if U_PAGE flag unset - lower memory
- Operation:
accessing memories serially like one after another.
by default, if U_PAGE is unset lower memory should accessible,
once user wants to access upper memory need to set U_PAGE.
Note: Technically there is only one CS line from the controller, but
zynq qspi controller has an internal hw logic to enable additional CS
when controller is configured for dual memories.
[1] http://www.xilinx.com/support/documentation/user_guides/ug585-Zynq-7000-TRM.pdf
--
Jagannadha Sutradharudu Teki <jaganna@xilinx.com>
05-01-2014.
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