Can I use the locked output of pll to generate a reset signal for my design? And what is the best reset mode for max10 ?using a input reset or generating a reset signal just in FPGA ？For my board,there is no input signal, how can I generate a internal reset ,can you give me a example for that ,or where I can find the reference?

Can I use the locked output of pll to generate a reset signal for my design?Yes , you can use it , but you have to be careful since when clock fails or skew or jitter or any issue related to the clock; PLL will lose it lock and it will reset your system. what is the best reset mode for max10 ? I am not following you , what you really menat by reset mode of max 10 ?For my board,there is no input signal, how can I generate a internal reset ,can you give me a example for that ,or where I can find the reference?Can you refer to your another post , I replied to thathttps://forums.intel.com/s/question/0D50P00004YEdCR/i-do-not-have-the-input-reset-signal-from-the-outside-of-the-altera-fpgaand-want-to-generate-reset-internallycan-i-do-like-below-Thank you, Regards,Sree

Very simple to do. Init a register to '0' and have it drive the RESET~ signal (ie, an active low reset).Then have a counter that starts at '0' and counts up for some number of bits (width depends on clock period and desired reset pulse width).When the counter overflows (or hits some predetermined value) set the register driving RESET~ to a '1', which deasserts reset.I have used this technique on various parts to, for example, generate a fixed 500ms reset pulse on FPGA powerup/configuration.No external reset input signal required.I used the onboard PLL to generate my system clock from the external 50MHz crystal oscillator input. I also used the 50MHz clock input to drive the reset generation logic (so it operates independent of the PLL).

oh,thanks very much!what about use the output of the pll to driver the reset generation logic ?Can the code below generate a reset correctly?always@(posedge sys_clk ) //sys_clk is a output of the pll and is 200Mhzbegin if(~locked_sig) reset_cnt <= 30'd0; else if(reset_cnt < 30'd200_000_005 ) // 1second to configure reset_cnt <= reset_cnt + 30'd1;end assign rst_n = (reset_cnt == 30'd200_000_001)?1'b0:1'b1;

Nope, I don't like that approach. Can't rely on SYS_CLK being valid if PLL is not locked.Here is what I do. I generate an async reset at powerup ONLY. Sync to PLL clock via dual rank sync circuit if sync reset is desired instead.// PowerUP Reset Logic // generate a 500ms reset pulse on initial powerup `ifdef SIMULATION reg [24:0] pup_count = 25'd24999900; `else reg [24:0] pup_count = 25'd0; `endif reg pup_reset = 1'b1; always @(posedge CLOCK_50) begin pup_count <= #TPD pup_count + 1'd1; if (pup_count == 25'd25000000) pup_reset <= #TPD 1'b0; end wire reset = pup_reset; PLL logic looks like this: // Altera PLL Clock module // Transform external crystal clock to our internal CPU clock wire pll_locked; wire CLOCK_CPU; pll pll ( .inclk0 (CLOCK_50), // input clock .locked (pll_locked), // status output .c0 (CLOCK_CPU) // output clock ); wire clk = CLOCK_CPU;

Sure ....but my only cocnern is what is the initial value of the counter register PUP_count ?Thank you , Regards,Sree

I design a board with max10,and do not design the reset input for max10, how can I generate a internal reset ?

13 Replies

SreekumarR_G_Intel
Frequent Contributor
6 years ago
Hello all,
Sorry i was caught up into different stuff ,
Actually in synthesis world reg [24:0] pup_count = 25'd0; is doesnt mean anything. if you think how you infer this as hardware i am not sure how to design or i can say there should be some define state to make sure it is set to Logic 0 or 1.
I have to check the LRM and Quartus synthesis tool to confrim by deafult the state of the reg type signal.
Also reg [24:0] pup_count = 25'd0; only used in Simulation not use in synthesis.
Hence if you want your design have valid state at reset kindly consider to use external Reset.
Sorry delay in repsonse again.
Thank you,
Regards,
Sree
ak6dn
Regular Contributor
6 years ago
Sorry Intel support person Sree you are misinformed and do not know what you are talking about.
I have been using the construct reg [24:0] pup_count = 25'd0; for YEARS now in the Quartus synthesis tools (at least since 11.0sp1) to assign the default initial powerup configuration of a register.
Using the external reset pin to feed into the async reset of a register is NOT necessary. The above construct works just fine for an initial powerup configuration.
Using the async reset pin is ONLY necessary if you want to perform that function AFTER initial powerup configuration.

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I design a board with max10,and do not design the reset input for max10, how can I generate a internal reset ?

13 Replies

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