Forum Discussion

fogl's avatar
fogl
Icon for Occasional Contributor rankOccasional Contributor
6 years ago

Soft LVDS Serdes

I am reading the Soft LVDS documentation (UG-M10LVDS | 2017.12.15) and some things seems strange:

  1. The block diagram on Figure2 shows that two clock sources (slow and fast) should be connected to soft serdes block. But i was not able to generate such a block. The generated block always requires fast clock only.

2. The waveform for x8 deserializer shows 10 bit RX_OUT[9:0], but the data is 8bit only. FCLK frequency is the same as data rate frequency, but when you generate the Soft LVDS block in Quartus, it shows a massage that the FCLK should be data rate frequency/2. 3. I am having problems setting the Soft LVDS for the fixed bit slip. I read one similar thread ( https://forums.intel.com/s/feed/0D50P00004YONUiSAP?language=en_US ), but i was not able to find a working solution. Can I write my own Soft LVDS block, do i have the access to all the hardware blocks - i was not able to find the HLD library for Max10 device to instantiate basic hardware blocks ( something similar to xilinx https://www.xilinx.com/support/documentation/sw_manuals/xilinx2012_2/ug953-vivado-7series-libraries.pdf ).

Regards

Klemen

4 Replies

  • Rahul_S_Intel1's avatar
    Rahul_S_Intel1
    Icon for Frequent Contributor rankFrequent Contributor
    6 years ago

    Hi ,

    Kindly find the inline answers

    Point no: 1 >> Those fast and slow clocks can be seen from the timing report not from the from the parameter setting of the serdes IP

    Reference page no: 33

    https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/hb/max-10/ug_m10_lvds.pdf

    Point no:2 > FCLK should be data rate frequency/2 , Where do you find the information.

    Point no:3 > Intel FPGA does not recommend to write own logic for serdes, so do not have any documentation for the reference.

  • fogl's avatar
    fogl
    Icon for Occasional Contributor rankOccasional Contributor
    6 years ago

    Thank you for your reply.

    1: Still it is no clear to me - is the slow clock required for the soft LVDS to function properly or not? I could not find the slow clock also on the Technology Map Viewer. From the block diagram one would assume the serdes can be synchronized to slow clock, but as i understand it, this is not possible to acommplish. The proper synchronization can be achieved with bitslip function and test data only?

    2. When you generate a Soft LVDS block you get some info:

    Info: lvdstest: Using the external PLL mode requires that:

    Info: lvdstest: (i) The fast clock (running at data rate /2) from the PLL feeds rx_inclock

    Info: lvdstest: (ii) The outputs be registered in the logic fed by the receiver

    Info: lvdstest: The receiver starts capturing the LVDS stream at the fast clock edge

    3. I just tried a simple code and it seems it works just fine.

    read_serdes_manual : process(clkfast_serdes)

    begin

    if rising_edge(clkfast_serdes) then

    clkslow_serdes_last <= clkslow_serdes; -- edge detection

    rx_dv <= '0'; -- default

    rx_serdes_data <= rx_serdes_data(6 downto 0) & rx_serdes_i;

    serdes_bit_cnt <= std_logic_vector(unsigned(serdes_bit_cnt) + 1);

    if clkslow_serdes = '1' and clkslow_serdes_last = '0' then -- rising edge on slow clock

    serdes_bit_cnt <= x"0";

    end if;

    if serdes_bit_cnt = x"1" then -- set fixed offset

    rx_data <= rx_serdes_data;

    rx_dv <= '1';

    end if;

    end if;

    end process;

    Regards

  • Rahul_S_Intel1's avatar
    Rahul_S_Intel1
    Icon for Frequent Contributor rankFrequent Contributor
    5 years ago

    Hi ,

    To answer your question , training pattern is required for synchronization