Entity: Gtx7RecClkMonitor

File: Gtx7RecClkMonitor.vhd

Diagram

Description

//////////////////////////////////////////////////////////////////////////////// // _ // / /\/ / // // \ / Vendor: Xilinx // \ \ \/ Version : 2.2 // \ \ Application : 7 Series FPGAs Transceivers Wizard // / / Filename : kintexgtxlowlat_recclk_monitor.vhd // // /\ // \ \ / \ // __\/___\ // // Description : This module is the ppm monitor between the GT RxRecClk and the reference clock

               This module will declare that the Rx RECCLK is stable if the                recovered clock is within +/-5000PPM of the reference clock.
                There are 3 counters running on local clocks for both                recovered clocks and one for the reference clock.  The                COUNTER_UPPER_VALUE parameter is the width of these                counters. The PPM offset is checked when these counters                roll over.
                There is also a counter running on the system clock.                This can be running at a much lower frequency and is                running on a BUFG.
                To set the parameters correctly here is what you need to                do.  Lets assume taht the reference and recovered                clocks are running at 156MHz and the system clock is                running at 50MHz.
                To ensure that the interval is long enough we want to                to make the COUNTER_UPPER_VALUE to be reasonable.  The                CLOCK_PULSES is the number of sytem clock cycles we can                expect to be off based on these frequencies:
                Example: Rec Clk and Ref Clk 156MHz, System clock 50MHz                         PPM Offset to tolerate +/- 5000PPM
                COUNTER_UPPER_VALUE = 15 -> 2^15 counter = 32768                GCLK_COUNTER_UPPER_VALUE = 15 -> 2^15 counter = 32768
                PPM OFFSET = 5000 => 32768 * 5000/1000000 = 164
                Now we are using the system clock to do the                calculations, therfore we need to scale the PPM_OFFSET                accordingly.
                CLOCK_PULSES = PPM_OFFSET * sysclk_freq/refclk_freq                             = 164 * 50/156 = 52
                When the counters are checked if they are off by less                than 52, we can delcare that the particular RECCLK is                stable.
                All FFs that have the _meta are metastability FFs and                can be ignored from a timing perspective. The following                constraint can be added to the UCF to ensure that they                are ignored:
                INST "*_meta" TNM = "METASTABILITY_FFS";                TIMESPEC "TS_METASTABILITY" = FROM FFS TO "METASTABILITY_FFS" TIG;

Module KintexGtxLowLat_RECCLK_MONITOR Generated by Xilinx 7 Series FPGAs Transceivers Wizard

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Generics

Generic name	Type	Value	Description
COUNTER_UPPER_VALUE	integer	20	ppm counter. For 2^20 cntr.
GCLK_COUNTER_UPPER_VALUE	integer	20	ppm counter. For 2^20 cntr.
CLOCK_PULSES	integer	5000
EXAMPLE_SIMULATION	integer	0	The simulation-only constructs are not used but the

Ports

Port name	Direction	Type	Description
GT_RST	in	std_logic
REF_CLK	in	std_logic
RX_REC_CLK0	in	std_logic
SYSTEM_CLK	in	std_logic	This would be your System Clock;
PLL_LK_DET	in	std_logic	This signal is verified in the Rx-FSM,
RECCLK_STABLE	out	std_logic	it can be tied high as the PLL-LK has already beenverified in the previous state.
EXEC_RESTART	out	std_logic

Signals

Name	Type	Description
state	FSM
ref_clk_cnt	std_logic_vector (COUNTER_UPPER_VALUE-1 downto 0)
rec_clk0_cnt	std_logic_vector (COUNTER_UPPER_VALUE-1 downto 0)
rec_clk0_msb	std_logic_vector (2 downto 1)
ref_clk_msb	std_logic_vector (2 downto 1)
rec_clk_0_msb_meta	std_logic
ref_clk_msb_meta	std_logic
sys_clk_counter	std_logic_vector (GCLK_COUNTER_UPPER_VALUE-1 downto 0)
rec_clk0_compare_cnt_latch	std_logic_vector (GCLK_COUNTER_UPPER_VALUE-1 downto 0)
ref_clk_compare_cnt_latch	std_logic_vector (GCLK_COUNTER_UPPER_VALUE-1 downto 0)
g_clk_rst_meta	std_logic
g_clk_rst_sync	std_logic
gt_pll_locked_meta	std_logic
gt_pll_locked_sync	std_logic
reset_logic_rec0_meta	std_logic
reset_logic_rec0_sync	std_logic
reset_logic_ref_meta	std_logic
reset_logic_ref_sync	std_logic
rec_clk0_edge_event	std_logic
ref_clk_edge_event	std_logic_vector (1 downto 0)
ppm0	std_logic_vector (GCLK_COUNTER_UPPER_VALUE-1 downto 0)
recclk_stable0	std_logic
reset_logic	std_logic_vector (3 downto 0)
ref_clk_edge_rt	std_logic_vector (1 downto 0)
g_clk_rst	std_logic
gt_pll_locked	std_logic
rec_clk0_edge	std_logic
ref_clk_edge	std_logic
recclk_stable0_int	std_logic

Constants

Name	Type	Value	Description
simulation	boolean	simulation_func

Types

Name	Type	Description
FSM	(WAIT_FOR_LOCK, REFCLK_EVENT, CALC_PPM_DIFF, CHECK_SIGN, COMP_CNTR, RESTART)

Functions

simulation_func () return boolean