Hi, I'm designing a pretty horrible board (33 page schematic!) that will use an Altera Arria II GX in the 572BGA package. There are 240 pure I/O pins in this package, and 12 dedicated clock pins. I'm getting close to using up all the i/o pins, and starting to do silly things to save a pin here and there. Don't blame me, blame customer feature creep! So, is it possible to use clock pins as general-purpose inputs? The documentation doesn't say so, but it does imply somewhere that clock nets can be used for non-clock functions like async resets, so there should be some not-too-disgusting way to used them as slow static inputs. Pity they didn't dual-purpose the clock pins. It's not often you need 12 clocks. Any thoughts/experience here? Thanks John
cheating Arria FPGA i/o count
Started by ●August 27, 2011
Reply by ●August 27, 20112011-08-27
On 28 Aug., 00:58, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> Hi, > > I'm designing a pretty horrible board (33 page schematic!) that will > use an Altera Arria II GX in the 572BGA package. There are 240 pure > I/O pins in this package, and 12 dedicated clock pins. I'm getting > close to using up all the i/o pins, and starting to do silly things to > save a pin here and there. Don't blame me, blame customer feature > creep! > > So, is it possible to use clock pins as general-purpose inputs? The > documentation doesn't say so, but it does imply somewhere that clock > nets can be used for non-clock functions like async resets, so there > should be some not-too-disgusting way to used them as slow static > inputs. > > Pity they didn't dual-purpose the clock pins. It's not often you need > 12 clocks. > > Any thoughts/experience here? > > Thanks > > Johnnever used altera, but I'd think it is in here somewhere: www.altera.com/download/board-layout-test/schematic-review-ws/worksheets/Arria_GX_Schematic_Review_Worksheet.doc -Lasse
Reply by ●August 27, 20112011-08-27
"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message news:3jsi579k5mhhectd2ej80jhme53h348ib5@4ax.com...> Hi, > > I'm designing a pretty horrible board (33 page schematic!) that will > use an Altera Arria II GX in the 572BGA package. There are 240 pure > I/O pins in this package, and 12 dedicated clock pins. I'm getting > close to using up all the i/o pins, and starting to do silly things to > save a pin here and there. Don't blame me, blame customer feature > creep! > > So, is it possible to use clock pins as general-purpose inputs? The > documentation doesn't say so, but it does imply somewhere that clock > nets can be used for non-clock functions like async resets, so there > should be some not-too-disgusting way to used them as slow static > inputs. > > Pity they didn't dual-purpose the clock pins. It's not often you need > 12 clocks. > > Any thoughts/experience here? > > Thanks > > John > >I don�t see why not, dedicated clocks mean that propagation time is minimized across the chip. But Quartus may balk at the idea. see <http://www.altera.com/literature/lit-dpcg.jsp> Some pins could be used as I/O , some can't. Cheers
Reply by ●August 27, 20112011-08-27
On Aug 27, 11:58=A0pm, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> Hi, > > I'm designing a pretty horrible board (33 page schematic!) that will > use an Altera Arria II GX in the 572BGA package. There are 240 pure > I/O pins in this package, and 12 dedicated clock pins. I'm getting > close to using up all the i/o pins, and starting to do silly things to > save a pin here and there. Don't blame me, blame customer feature > creep! > > So, is it possible to use clock pins as general-purpose inputs? The > documentation doesn't say so, but it does imply somewhere that clock > nets can be used for non-clock functions like async resets, so there > should be some not-too-disgusting way to used them as slow static > inputs. > > Pity they didn't dual-purpose the clock pins. It's not often you need > 12 clocks. > > Any thoughts/experience here? > > Thanks > > JohnJust did a test design using an Arria II GX and assigned an input pin to a dedicated clock input and it compiled OK.
Reply by ●August 27, 20112011-08-27
On Aug 28, 12:43=A0am, davew <david.wo...@gmail.com> wrote:> On Aug 27, 11:58=A0pm, John Larkin > > > > > > <jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > > Hi, > > > I'm designing a pretty horrible board (33 page schematic!) that will > > use an Altera Arria II GX in the 572BGA package. There are 240 pure > > I/O pins in this package, and 12 dedicated clock pins. I'm getting > > close to using up all the i/o pins, and starting to do silly things to > > save a pin here and there. Don't blame me, blame customer feature > > creep! > > > So, is it possible to use clock pins as general-purpose inputs? The > > documentation doesn't say so, but it does imply somewhere that clock > > nets can be used for non-clock functions like async resets, so there > > should be some not-too-disgusting way to used them as slow static > > inputs. > > > Pity they didn't dual-purpose the clock pins. It's not often you need > > 12 clocks. > > > Any thoughts/experience here? > > > Thanks > > > John > > Just did a test design using an Arria II GX and assigned an input pin > to a dedicated clock input and it compiled OK.If you're not sure, assign the pin and run the I/O Assignment Analysis. This validates all your I/O assignments without having to compile any code.
Reply by ●August 27, 20112011-08-27
On Sat, 27 Aug 2011 16:43:03 -0700 (PDT), davew <david.wooff@gmail.com> wrote:>On Aug 27, 11:58�pm, John Larkin ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> Hi, >> >> I'm designing a pretty horrible board (33 page schematic!) that will >> use an Altera Arria II GX in the 572BGA package. There are 240 pure >> I/O pins in this package, and 12 dedicated clock pins. I'm getting >> close to using up all the i/o pins, and starting to do silly things to >> save a pin here and there. Don't blame me, blame customer feature >> creep! >> >> So, is it possible to use clock pins as general-purpose inputs? The >> documentation doesn't say so, but it does imply somewhere that clock >> nets can be used for non-clock functions like async resets, so there >> should be some not-too-disgusting way to used them as slow static >> inputs. >> >> Pity they didn't dual-purpose the clock pins. It's not often you need >> 12 clocks. >> >> Any thoughts/experience here? >> >> Thanks >> >> John > >Just did a test design using an Arria II GX and assigned an input pin >to a dedicated clock input and it compiled OK.Cool! I'll have one of my FPGA guys try it, maybe on a real eval board (I don't drive the FPGA software myself.) This very weekend, I'll assume it works and get on with my life. Thanks John
Reply by ●August 28, 20112011-08-28
On Sat, 27 Aug 2011 22:44:14 -0700, Robert Baer <robertbaer@localnet.com> wrote:>davew wrote: >> On Aug 27, 11:58 pm, John Larkin >> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >>> Hi, >>> >>> I'm designing a pretty horrible board (33 page schematic!) that will >>> use an Altera Arria II GX in the 572BGA package. There are 240 pure >>> I/O pins in this package, and 12 dedicated clock pins. I'm getting >>> close to using up all the i/o pins, and starting to do silly things to >>> save a pin here and there. Don't blame me, blame customer feature >>> creep! >>> >>> So, is it possible to use clock pins as general-purpose inputs? The >>> documentation doesn't say so, but it does imply somewhere that clock >>> nets can be used for non-clock functions like async resets, so there >>> should be some not-too-disgusting way to used them as slow static >>> inputs. >>> >>> Pity they didn't dual-purpose the clock pins. It's not often you need >>> 12 clocks. >>> >>> Any thoughts/experience here? >>> >>> Thanks >>> >>> John >> >> Just did a test design using an Arria II GX and assigned an input pin >> to a dedicated clock input and it compiled OK. > Just because a program compiles does not mean it will work...It does mean the I/O assignment meets the chip's specs, which is all that was asked.
Reply by ●August 28, 20112011-08-28
davew wrote:> On Aug 27, 11:58 pm, John Larkin > <jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> Hi, >> >> I'm designing a pretty horrible board (33 page schematic!) that will >> use an Altera Arria II GX in the 572BGA package. There are 240 pure >> I/O pins in this package, and 12 dedicated clock pins. I'm getting >> close to using up all the i/o pins, and starting to do silly things to >> save a pin here and there. Don't blame me, blame customer feature >> creep! >> >> So, is it possible to use clock pins as general-purpose inputs? The >> documentation doesn't say so, but it does imply somewhere that clock >> nets can be used for non-clock functions like async resets, so there >> should be some not-too-disgusting way to used them as slow static >> inputs. >> >> Pity they didn't dual-purpose the clock pins. It's not often you need >> 12 clocks. >> >> Any thoughts/experience here? >> >> Thanks >> >> John > > Just did a test design using an Arria II GX and assigned an input pin > to a dedicated clock input and it compiled OK.Just because a program compiles does not mean it will work...
Reply by ●August 28, 20112011-08-28
"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message news:3jsi579k5mhhectd2ej80jhme53h348ib5@4ax.com...> Hi, > > I'm designing a pretty horrible board (33 page schematic!) that will > use an Altera Arria II GX in the 572BGA package. There are 240 pure > I/O pins in this package, and 12 dedicated clock pins. I'm getting > close to using up all the i/o pins, and starting to do silly things to > save a pin here and there. Don't blame me, blame customer feature > creep! > > So, is it possible to use clock pins as general-purpose inputs? The > documentation doesn't say so, but it does imply somewhere that clock > nets can be used for non-clock functions like async resets, so there > should be some not-too-disgusting way to used them as slow static > inputs. > > Pity they didn't dual-purpose the clock pins. It's not often you need > 12 clocks. > > Any thoughts/experience here? > > Thanks > > John > >Does PS boot mode save a pin or two ?..
Reply by ●August 28, 20112011-08-28
> So, is it possible to use clock pins as general-purpose inputs?For Altera Cyclone X, you can use clock-inputs as general-purpose inputs with some restrictions, most important: - No internal pullups possible - No fast I/O-register It is not possible to use them as output. I guess, the same applies also for the Arria-parts, but I have not double-checked. Regards, Thomas www.entner-electronics.com
