OPOS6UL SP Interfaces description

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This article describe the bus interface communication between the i.MX6UL(L) and the spartan6. In i.MX6UL(L) the bus used to make communication with the FPGA is named EIM for External Interface Module. All description of this bus can be found under the i.MX6UL(L) reference manual in chapter 21 (page 821).

FPGA used on board is an XC6SLX9-2CSG225.

Simplified view

figure 1 - i.MX6UL(L)-Spartan6 bus description

Normal communication between i.MX6UL(L) processor and Spartan6 fpga is done with black following signals :

  • EIM_BCLK : Clock
  • EIM_DA[15:0]: 16bits data and address bus
  • EIM_LBA (ADV): Signal used for data/address muxing
  • EIM_RW: Read/Write control signal
  • EIM_CS0: Chip select

Gray following signals can be used by EIM (External Interface Memory), but not used in default configuration :

  • EIM_EB0: Select byte 0 on bus
  • EIM_EB1: Select byte 1 on bus
  • OE : Output enable
  • EIM_CLK0: second clock (EIM_ACLK)

Blue following signals are used for FPGA configuration from imx. Some EIM (black) signals are also used for it.

  • FPGA_INITB: Initialize FPGA
  • FPGA_PROGRAM : Program (configure) FPGA
  • FPGA_DONE: FPGA configuration is done.


Default configuration on CSx


The clock used to clock the FPGA is EIM_BCLK (IO_L1P_CCLK_2(N12) and IO_L29P_GCLK3_2(N8)) and is configured to 99 MHz.

Chip Select

The EIM memory space is mapped into 128 MB total memory space in the processor memory. This memory space begin at address 0x50000000.

Start address End address Size Name
0x5000_0000 0x57FF_FFFF 128 MB EIM (NOR/SRAM)

The total 128 MB of memory can be divided among the EIM four chip selects. See reference manual of i.MX6ULL for more information.



  • U-Boot: To read one 16 bits value in 0 (0x50000000 in i.MX) do :
BIOS> md.w 50000000 1
  • Linux: To read one 16 bits value in 0 (0x50000000 in i.MX) do :
# devmem 0x50000000 16
  • Bus timings are following :


  • U-Boot: To write one 16 bits value in 0 (0x50000000 in i.MX) do :
BIOS> mw.w 50000000 CAFE
  • Linux: To write one 16 bits value in 0 (0x50000000 in i.MX) do :
# devmem 0x50000000 16 0xCAFE
  • Bus timings are following :

code & mapping


Schematics interfaces is given here :

Opos6ul sp sch int.jpg

UCF example for interface generated by POD is given here :

NET "rstgen_syscon00_ext_clk" LOC="N8" | IOSTANDARD=LVCMOS33; # EIM_BCLK
NET "rstgen_syscon00_ext_clk" TNM_NET = "rstgen_syscon00_ext_clk";
TIMESPEC "TS_rstgen_syscon00_ext_clk" = PERIOD "rstgen_syscon00_ext_clk" 10.101 ns HIGH 50 %;
NET "imx6ul_wb16_wrapper00_imx_da<0>" LOC="P11" | IOSTANDARD=LVCMOS33; # EIM_DA0
NET "imx6ul_wb16_wrapper00_imx_cs_n" LOC="R11" | IOSTANDARD=LVCMOS33; # EIM_CS0
NET "imx6ul_wb16_wrapper00_imx_da<1>" LOC="M11" | IOSTANDARD=LVCMOS33; # EIM_DA1
NET "imx6ul_wb16_wrapper00_imx_da<2>" LOC="N11" | IOSTANDARD=LVCMOS33; # EIM_DA2
NET "imx6ul_wb16_wrapper00_imx_da<10>" LOC="R10" | IOSTANDARD=LVCMOS33; # EIM_DA10
NET "imx6ul_wb16_wrapper00_imx_da<11>" LOC="L9" | IOSTANDARD=LVCMOS33; # EIM_DA11
NET "imx6ul_wb16_wrapper00_imx_da<12>" LOC="M10" | IOSTANDARD=LVCMOS33; # EIM_DA12
NET "imx6ul_wb16_wrapper00_imx_da<13>" LOC="M8" | IOSTANDARD=LVCMOS33; # EIM_DA13
NET "imx6ul_wb16_wrapper00_imx_da<14>" LOC="K8" | IOSTANDARD=LVCMOS33; # EIM_DA14
NET "imx6ul_wb16_wrapper00_imx_da<15>" LOC="L8" | IOSTANDARD=LVCMOS33; # EIM_DA15
NET "imx6ul_wb16_wrapper00_imx_adv" LOC="R7" | IOSTANDARD=LVCMOS33; # EIM_LBA
NET "imx6ul_wb16_wrapper00_imx_da<7>" LOC="N6" | IOSTANDARD=LVCMOS33; # EIM_DA7
NET "imx6ul_wb16_wrapper00_imx_rw" LOC="R6" | IOSTANDARD=LVCMOS33; # EIM_RW
NET "imx6ul_wb16_wrapper00_imx_da<3>" LOC="P5" | IOSTANDARD=LVCMOS33; # EIM_DA3
NET "imx6ul_wb16_wrapper00_imx_da<4>" LOC="R5" | IOSTANDARD=LVCMOS33; # EIM_DA4
NET "imx6ul_wb16_wrapper00_imx_da<5>" LOC="L6" | IOSTANDARD=LVCMOS33; # EIM_DA5
NET "imx6ul_wb16_wrapper00_imx_da<6>" LOC="L5" | IOSTANDARD=LVCMOS33; # EIM_DA6
NET "imx6ul_wb16_wrapper00_imx_da<8>" LOC="M5" | IOSTANDARD=LVCMOS33; # EIM_DA8
NET "imx6ul_wb16_wrapper00_imx_da<9>" LOC="N5" | IOSTANDARD=LVCMOS33; # EIM_DA9
NET "irq_mngr00_gls_irq" LOC="P3" | IOSTANDARD=LVCMOS33; # FPGA_INITB

Simulation model

Some simulation model has been written to test eim in VHDL and in python with cocotb.


imx_read and imx_write simulation fonctions are included in POD (Peripheral On Demand) library. Available in platform/opos6ulsp directory.


It's possible to simulate eim access with cocotb module named cocotbext-imxeim.

HDL bus wrapper

Bus wrapper has been written in VHDL and chisel to convert EIM protocol to Wishbone bus protocol.


A 16 bits multiplexed EIM to 16bits wishbone master bus is available in POD library. The VHDL sources are available following this link.


A chisel package is available in module chisArmadeus to drive Wishbone master bus with EIM bus here.

FPGA Interrupt

To generate an IRQ from the FPGA to the i.MX, the pin FPGA_INITB is used by default. It correspond to GPIO4_IO16 on i.MX.

FPGA J2 connector mapping

Mapping of FPGA pin is given in following csv file.

FPGA configuration protocol



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