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Altera_Forum's avatar
Altera_Forum
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12 years ago

Issue with the application layer from NIOS II IDE while accessing a custom instructio

Hello,

I have implemented a custom instruction for full adder (just a basic one) in verilog for NIOS II.

However when my application code (C) from NIOS II tries to access the macro for the custom instruction, I

see one input operand value being tried up to a strange value, 2047 (!). Any guess what might be causing the issue?

I have checked almost all the sides, however I could not find the issue.

I am attaching the verilog modules with this email, I have tested in Modelsim and there it works good.

I am pasting the valid instructions from the file custom_add_hw.tcl below:

"add_interface nios_custom_instruction_slave_0 nios_custom_instruction end

set_interface_property nios_custom_instruction_slave_0 clockCycle 0https://www.alteraforum.com/forum/attachment.php?attachmentid=6957

set_interface_property nios_custom_instruction_slave_0 operands 2

set_interface_property nios_custom_instruction_slave_0 ENABLED true

add_interface_port nios_custom_instruction_slave_0 clk clk Input 1

add_interface_port nios_custom_instruction_slave_0 reset reset Input 1

add_interface_port nios_custom_instruction_slave_0 dataa dataa Input 32

add_interface_port nios_custom_instruction_slave_0 datab datab Input 32

add_interface_port nios_custom_instruction_slave_0 n n Input 3

add_interface_port nios_custom_instruction_slave_0 clk_en clk_en Input 1

add_interface_port nios_custom_instruction_slave_0 start start Input 1

add_interface_port nios_custom_instruction_slave_0 done done Output 1

add_interface_port nios_custom_instruction_slave_0 result result Output 32"https://www.alteraforum.com/forum/attachment.php?attachmentid=6957 https://www.alteraforum.com/forum/attachment.php?attachmentid=6958 https://www.alteraforum.com/forum/attachment.php?attachmentid=6959

Now from the NIOS II IDE, I am trying to call the custom instruction using the macro

sumOutput = ALT_CI_CUSTOM_ADD_INST(4,1,10); as shown in the attached .c file.

However the output I am getting is,

Hello from Nios II!

The sum is 2057

which is 2047 (for dataa, I donno why) + 10 (for datab, which gets proper value).

Please help me in solving this issue.

Thank You,

Akhil

3 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    12 years ago

    Hello,

    Can someone be of assistance to this post please? I am struck at this point in the simulation, appreciate any inputs.

    If the post is not clear, I can explain the scenario once again.

    Thank You,

    Akhil
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    12 years ago

    Hello,

    Sorry, it had been my fault in the verilog and the fault was with respect to the timing.

    Earlier, I had been trying to do the ADD operation and read the result output port in the same clock cycle which was making the module confused

    and I guess the dataa port had been getting unknown value (like 2047) because of that timing issue. I really appreciate for BadOmen who made me

    to look into the custom instruction timing diagram once again (I am just a beginner).

    See what I did now is having separate 'write' and 'read' instructions and added the lines of code in verilog module custom_Component.v

    if(write && chipselect) begin

    cin = 0;

    {cout, output_value} = writedataa + writedatab + cin;

    end

    else if((read == 1) && (chipselect == 1))

    begin

    readdata <= output_value;

    end

    so that before reading a result port, there will be a write latency.

    I tried to access from the application code (in NIOS II IDE) like this:

    /* Write Sum */ dataa = 0XFFFFFFFF;

    datab = 0XFFFFFFFF;

    sumOutput = ALT_CI_CUSTOM_ADD_INST(1,dataa,datab);

    printf("\nThe result line value is %lu",sumOutput); // Expect some unknown value to print

    /* Read Sum */

    sumOutput = ALT_CI_CUSTOM_ADD_INST(4,dataa,datab); // Expect the earlier SUM value to print

    printf("\nThe SUM of %lu and %lu is %lu",dataa,datab,sumOutput);

    And the sumOutput variable printed an expected value!.

    I appreciate the effort taken by forum admins to sort this out.

    Thank You,

    Akhil