Glitch free clock mux

Zerodelay glitchfree clock multiplexer mds 58101, 58102 b 1 revision 062602 integrated circuit systems, inc. Glitchfree clock transition is required in modern electronic systems because a low frequency clock such as 25 mhz is typically distributed, and thereafter multiplied with phase lock loops plls. And thats right about when they get blindsided by a glitch. Using bufgmux ensures glitchfree switching between the clocks. At chip startup time, both flip flops dff0 and dff1 should be reset to the zero state so. In this paper nand based dcdl present the glitch free circuits by the control switching of the delay. Many approaches are known to avoid glitching in mux based dcdls 2123. In addition, a unique failsafe input protection prevents metastable conditions when the selected input clock fails to a dc voltage voltage between the pins of the differential input drops below 200mv.

Apr 04, 2017 if the selected clock becomes disabled, techniques described herein can be used to automatically switch to an active clock, in a glitch free manner, to prevent interruption of the system operation. But even the circuit can switch to it, it is just static and not much different from current way. In most common application dcdl is used to process the clock signal, therefore glitch free dcdl operation is required. Free shifting circuit timing and power challenges are also felt in the emerging market of pc computer. Within the metastability recovery imposed flip flop speed limit it should be glitch free. Refer to your ip core user guide for information about specific ip core parameters. During synthesis i faced several problems with this module which gave some bad performance in terms of clock timing. The device is designed to switch between two clocks, whether running or not. Proposed dcdls have been designed in a 90nm cmos technology. The ics58101 is a glitch free, phase locked loop pll based clock multiplexer mux with zero delay from input to output. If you use a fabricbased mux rather than bufgmux, switchover between clock sources will not be clean. By combining the clocks with an or gate and gating all clocks off before switching from one clock to another, a glitch free train of clock pulses can be created from individual clock inputs. The proper driving circuits are also designed to drive the control bits to the dcdl with the timing constrain for the delay control code. This component contains the verified rtl code of the clock switch as well as documentation and timing and.

A glitch free clock switching circuit includes a first enable synchronization logic that generates a first clock enable in response to a first enable from a first enable generation logic. Sy89841u clock and timing clock and data distribution. Figure 3 you can map a simple, glitch free multiplexer a with and and or gates that can create glitches b. Techniques to make clock switching glitch free with more and more multifrequency clocks being used in todays chips, especially in the communications field, it is often necessary to switch the source of a clock line while the chip is running. I have it implemented and it works well except two potential issues. Rhoney has a good intro about glitch free clock mux ing. Glitchfree clock multiplexer amazon technologies, inc. The hazard of generating a glitch on a clock line while switching between clock sources can be avoided with very little overhead by using the design techniques presented in this article. As long as source clock toggles, clock muxing output will be 0 in this case since source clock path is turned off. Zero delay glitchfree clock multiplexer ics5810102 idt zero delay glitchfree clock multiplexer 1 ics5810102 rev m 110216 description the ics5810102 are glitch free, phase locked loop pll based clock multiplexers mux with zero delay from input to output. When clk0 is off, enb0 becomes 1 and this will turn on clk1 path. Free frequency shifting simplifies timing design silicon labs.

Each clock depends on the other clock being disabled before enabling. Glitch free strobe control based digitally controlled delay lines. Sample clock mux circuits and how to constrain them in the timing analyzer. Other designs are tree based mux delay unit, inverter based. This circuit is supposed to be glitch free but its. A clock multiplexer switches the clock without any glitches as the glitch in clock will. Only one input clock signal will be select as output clock according to these tree select signals. The input are three clocksclk1,clk2,clk3, and three select signalssel1, sel2, sel3. A glitchfree mux is a state machine, which means that one way or another, it must have internal feedback, creating latches. Clock switching is commonly used in asic and fpga design. To comprehend these risks, consider a simple example of a glitch free multiplexer. Clock mux for allowing glitchfree muxing of asynchronous. Glitch free frequency shifting simplifies timing design in. The following shows three example circuits and the appropriate sdc commands to constrain them.

When selb changes, the output clock goes low after 3 cycles of the output clock. The ics58101 and ics58102 are glitch free, phase locked loop pll based clock multiplexers mux with zero delay from input to output. An improved glitchfree clock switching circuit is proposed, which introduces fault tolerant function that is able to switch away from a failed clock, and adds. Actually above circuit is flawed or has limitation. Clock gating checks on multiplexers design and reuse. Glitch free clock multiplexer mds 58001 b 3 revision 011602 integrated circuit systems, inc. The ics58001 is a clock multiplexer mux designed to switch between 2 clock sources with no glitches or short pulses. A fully digital glitch free clock multiplexer includes a monitoring circuit that automatically switches to a newly selected clock, after a defined time period, from a currently selected clock, when the currently selected clock is absent.

Clock mux for allowing glitchfree muxing of asynchronous clocks. Glitch free clock transition is required in modern electronic systems because a low frequency clock such as 25 mhz is typically. Techniques to make clock switching glitch free ee times. The circuit facilitates glitch free clock multiplexing. Newest vhdl questions feed to subscribe to this rss feed, copy and paste this url into your rss reader. Glitchfree clock mulitplexer clock multiplexer idt ics glitchfree clock mulitplexer 4 ics58001 rev k 092509 device operation the ics58001 consists of a glitch free mux between ina and inb controlled by selb.

Clock mux maximum possible frequency at the output is 200 mhz. Is it possible to generated a combinational clock mux that. Control circuitry going to the individual clock gaters provides the ability to shut all clocks off for a period of time equal to the longest clock period. Actually, i do not intend to discuss all the details of glitchfree clock muxing, a nice and very. How to verify glitch free mux verification academy. Us9360883b1 clock multiplexer for generating glitchfree. Trydeman posts two issues about this glitch free clk switching circuit at two potential issues with glitch free clock muxing good thinking. Downstream tools, such as synthesis, optimization, and technology mapping, can transform the circuit and introduce. Clock mux for allowing glitch free muxing of asynchronous clocks.

The clocking architecture of a design needs to be modified to support scan operation. Two potential issues with glitch free clock muxing valpont. A necessary condition to avoid glitching is designing a dcdl which have no glitch in presence of a delay controlcode switching. Glitches in synchronous paths are momentary and mostly harmless. They do not last long enough to meet the setuphold requirement of the next active synchronous clock edge, and static timing. Glitch free strobe control based digitally controlled. The proposed glitch free strobecontrol based digitally controlled delay lines maintains the same resolution and minimum delay of previously proposed glitch free nandbased dcdl. Clock control block altclkctrl ip core april 2018 altera corporation user guide 3. The output of mux is glitch free clock the select signal is toggling at different time. Blindsided by a glitch tech design forum techniques.

Also, in clock gating checks at a multiplexer, we discussed the conditions wherein a normal multiplexer can be used to propagate. The assertion of the common hold signal precedes a chance in state of the selection signal and endures at least until all the hold signals have been asserted and a change in state of the selection signal has occurred. A clock glitchfree clock multiplexer serves to switch between two asynchronous clocks while protecting downstream logic from clock glitches. The last patch is a small improvement for the vpu clock so we utilize the glitch free mux on socs which support it and avoid problems by changing the live clock tree at runtime with the mali clock this resulted in system hangsfreezes. A clock multiplexer clock mux selects one of the several inputs and propagates that signal forward. Datasheet zero delay glitchfree clock multiplexer ics5810102 idt ics zero delay glitchfree clock multiplexer 1 ics5810102 rev l 0510 description the ics5810102 are glitch free, phase locked loop pll based clock multiplexers mux with zero delay from. The 58001 is a clock multiplexer mux designed to switch between two clock sources with no glitches or short pulses. The deglitch clock mux also enables switching when one or both of the clocks are not toggling. Embodiments of the disclosed technologies provide methods for clock multiplexing which can perform glitch free clock switching between two clocks. As can be seen, the key idea to do glitch free clock switching is to turn off one clock before turning on the other one. Glitchfree clock multiplexer mds 58001 b 3 revision 011602 integrated circuit systems, inc.

About me i work as an ip design engineer in a product based semiconductor. Since the fsm controlling the select pin of clock mux will be part of scan chains, it will toggle during testing. If wed like to switch from clk1 to clk0, clk1 can not be off. A clock glitch free clock multiplexer serves to switch between two asynchronous clocks while protecting downstream logic from clock glitches. Figure 3 glitch free clock switching for unrelated clocks. How to write a glitchfree clock multiplexer by verilog language.

Bind interface uvm issue functional verification cadence. These clock frequencies can be totally unrelated or they may be multiples of each other. The idea is to switch the clock when the orginally selected clock line are at logic 0, wait for 2 clock cycle or so, then ramp up to the newly. Unlike standard multiplexers, the sy89841u unique 2. The timing analyzer makes it easy to use synopsys design constraint sdc commands to constrain complex clock structures, such as multiplexed clocks. In the first example, clocks are running on both ina and inb. The two frequencies may be related to each other, or may to totally unrelated.

While it is possible to build asynchronous state machines using luts only, the tools will complain mightily, and the performance will be worse than if you use actual registers ffs. Hence the clock at the output of the clock mux becomes unpredictable and can be any one of its input at any instance. Idt offers several types of clock multiplexers that not only include a multiplexing function, but also clock divider and fanout buffer functions integrated on the same device. Device operation and applications the ics58001 consists of a glitch free mux between ina. How to verify whether the output clock has really glitch free or not using automation. Maybe i missed this thread the other day when i was responding to other posts. Glitch free clock switching techniques in modern microcontrollers borisav jovanovic, milunka damnjanovic abstract multifrequency clock signals are being widely used in chips, especially in the communications area. In this paper nand based dcdl present the glitch free circuits by the control switching of the delay control codes. Mar 11, 2016 glitch free clock gating verilog good clock gating by unknown at friday, march 11, 2016 good clock gating, verilog clock gating, verilog codes, vlsi 3 comments clock gating is a popular technique used in many synchronous circuits for reducing dynamic power dissipation. Glitchfree nandbased digitally controlled delaylines. Digitally controlled delay lines based on nand gate for. Proceedings of the 5th small systems simulation symposium.

Ics58101, 02 zerodelay glitchfree clock multiplexer. The si535051 supports an innovative glitchfree frequency switching feature that eliminates glitches and runt pulses during output clock frequency transition. How to write a glitch free clock multiplexer by verilog language. It has have four low skew outputs which can be configured as a single output, three outputs. Glitch free clock gating verilog good clock gating elecdude. How to verify whether the output clock has really glitch free.

Device operation and applications the ics58001 consists of a glitch free mux between ina and inb controlled by selb. Glitch free clock multiplexer circuit 3com corporation. There are two directions of operation of glitch free multiplexer 20 in switching from an active clock currently in service to a clock being switched into service. In this article we will take an example of a very generic functional clocking architecture as shown in figure 1 and modify it. When select becomes 1, enb00 will hold clk1 turned off. Specify the parameters and options for your ip variation in the parameter editor, including one or more of the following. Rafey mahmud had an article talking about glitch free clock switching at.

Following this analysis, three driving circuits for the delay controlbits are also proposed. Oct 18, 1994 the operation of glitch free multiplexer 20 is best understood with reference to the schematic diagram of fig. The great thing about the bufgctrl is that it allows you to switch between clocks glitch free. The device is designed to switch between 2 clocks, whether running or not. The input are three clocks clk1,clk2,clk3, and three select signalssel1, sel2, sel3. Ics58001 glitchfree clock multiplexer datasheet catalog. Is it possible to generated a combinational clock mux that is. Sy89838u clock and timing clock and data distribution.

Also, in clock gating checks at a multiplexer, we discussed the conditions wherein a normal multiplexer can be used to propagate a clock without any glitches. The sy89838u distributes clock frequencies from 1khz to 1. Zero delay glitchfree clock multiplexer the ics58101 is a glitch free, phase locked. The si535051 is the industrys most flexible cmos clock generator capable of supporting any. Apparatus for glitchfree switching between multiple asynchronous clock sources on an integrated circuit. Timing analyzer clock multiplexer examples the timing analyzer makes it easy to use synopsys design constraint sdc commands to constrain complex clock structures, such as multiplexed clocks. A glitch free mux is a state machine, which means that one way or another, it must have internal feedback, creating latches. So this clock is turned on after all the other clocks are turned off. Clock multiplexer for glitchfree clock switching vlsi universe. Using bufgmux ensures glitch free switching between the clocks. Clock domain crossing coming soon reset domain crossing coming soon a top view of vlsi design flow coming soon. Youll just hafta take into account the delay through the syncronizer. I found a good paper some weeks ago for this topic, but currently i cant find the online source.