| Number | 547
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| Category | enhancement
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| Synopsis | define size zero replication constant
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| State | lrmdraft
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| Class | enhancement
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| Arrival-Date | Feb 19 2004
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| Originator | Shalom.Bresticker@motorola.com
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| Release | 2001c: 4.1.14
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| Description |
In 1364-2001, we have defined a replication constant of zero to be illegal. In my company, using parameters for various values, we have repeatedly found that it would be useful for a replication constant of zero to be defined. Typically it is used as part of a larger concatenation. I would expect a zero replication to be null, that is, {1'b1, {0{1'b0}}, 1'b1} would give me 2'b11. -- Shalom Bresticker Shalom.Bresticker@motorola.com Design & Reuse Methodology Tel: +972 9 9522268 Motorola Semiconductor Israel, Ltd. Fax: +972 9 9522890 POB 2208, Herzlia 46120, ISRAEL Cell: +972 50 441478 [x]Motorola General Business Information [ ]Motorola Internal Use Only [ ]Motorola Confidential Proprietary |
| Fix |
In 4.1.14 (Concatenations): CHANGE "An operator that can be applied only to concatenations is replication, which is expressed by a concatenation preceded by a positive, non-x and non-z constant expression, enclosed together within brace characters, and which indicates a joining together of that many copies of the concatenation." TO "An operator that can be applied only to concatenations is replication, which is expressed by a concatenation preceded by a non-negative, non-x and non-z constant expression, called a replication constant, enclosed together within brace characters, and which indicates a joining together of that many copies of the concatenation." DELETE the example {0{1'b0}} // illegal At the end of 4.1.14, ADD the following: A replication operation may have a replication constant with a value of zero. This is useful in parameterized code. A replication with a zero replication constant is considered to have a size of zero and is ignored. Such a replication shall appear only within a concatenation in which at least one of the operands of the concatenation has a positive size. Examples: parameter P = 32; // The following is legal for all P from 1 to 32 assign b[31:0] = { {32-P{1'b1}}, a[P-1:0] } ; // The following is illegal for P=32, // because the zero replication appears alone within a concatenation assign c[31:0] = { {{32-P{1'b1}}}, a[P-1:0] } ; // The following is illegal for P=32 initial $displayb({32-P{1'b1}}, a[P-1:0]); |
| Audit-Trail |
From: Shalom.Bresticker@freescale.com To: btf-bugs@boyd.com Cc: Subject: Re: enhancement/547: define size zero replication constant Date: Sun, 30 May 2004 08:24:43 +0300 (IDT) An independent development of the same enhancement: ---------- Forwarded message ---------- Date: 28 May 2004 23:03:05 GMT From: Steve Meyer <sjmeyer@www.tdl.com> Reply-To: sjmeyer@pragmatic-c.com Newsgroups: comp.lang.verilog Subject: Re: Repeat concatenation and Modelsim GPL Cver allows 0 width concats because a user we were not matching XL. The algorithm is that a 0 repeat count removes the element. It is then an error if the entire concatenate disappers (i.e. becomes zero width). Here is the bug report test: ============ module top; reg [10:0] rf_addr_ext; reg [10:0] rf_addr; parameter AW = 5; parameter DW = 5; initial begin rf_addr_ext = {{AW - DW{1'b0}}, rf_addr}; end endmodule ============ On Tue, 25 May 2004 16:18:38 +0100, DW <dave_wooff@hotmail.com> wrote: > Hello, > Can anyone confirm that the Verilog language definition rules out a repeat > concatenation of 0. i.e. > {0{1'b1}} is NOT allowed. > > Modelsim Altera v5.7e seems to let this pass and produces invalid code. > Quartus II version 3.0 seems to reject the use of this, although I have been > informed that a later release (version 4.0 I believe) allows it (when it > apparently should not). > > Although the example given is simplistic, I had used a combination of > defparam'd parameters which produced the 0 repeat. I do not have a complete > language reference (could be a good investment). From: Shalom.Bresticker@freescale.com To: etf-bugs@boyd.com Cc: Subject: Re: enhancement/547: define size zero replication constant Date: Fri, 22 Oct 2004 11:44:11 +0200 (IST) On Thu, 19 Feb 2004, Shalom Bresticker wrote: > In 1364-2001, we have defined a replication constant of zero to be illegal. > > In my company, using parameters for various values, we have repeatedly > found that it would be useful for a replication constant of zero to be > defined. Typically it is used as part of a larger concatenation. > > I would expect a zero replication to be null, that is, > {1'b1, {0{1'b0}}, 1'b1} would give me 2'b11. PROPOSAL: In 4.1.14 (Concatenations): In the paragraph beginning, "Another form of concatenation is the replication operation. The first expression shall be a constant expression with a positive integral value," CHANGE "positive" to "non-negative". At the end of 4.1.14, ADD the following: A replication operation may have a replication constant with a value of zero. This is useful in parameterized code. A replication with a zero replication constant is considered to have a size of zero and is ignored. A zero replication shall appear only within a concatenation in which at least one of the operands of the concatenation has a positive size. Examples: parameter P = 8; reg[31:0] r ; reg[P-1:0] a ; r = { {16{1'b1}}, 16-P{1'b0}, a[P-1:0]} ; // legal - For P=8, this is {16{1'b1}}, 8{1'b0}, a[7:0]} // legal - For P=16, this is {16{1'b1}}, a[15:0]} -- Shalom Bresticker Shalom.Bresticker @freescale.com Design & Verification Methodology Tel: +972 9 9522268 Freescale Semiconductor Israel, Ltd. Fax: +972 9 9522890 POB 2208, Herzlia 46120, ISRAEL Cell: +972 50 5441478 [ ]Freescale Internal Use Only [ ]Freescale Confidential Proprietary From: Shalom.Bresticker@freescale.com To: etf-bugs@boyd.com Cc: Subject: Re: enhancement/547: define size zero replication constant Date: Fri, 22 Oct 2004 11:47:32 +0200 (IST) Sorry, did not mean to send that yet. I was working on a draft of a proposal. -- Shalom Bresticker Shalom.Bresticker @freescale.com Design & Verification Methodology Tel: +972 9 9522268 Freescale Semiconductor Israel, Ltd. Fax: +972 9 9522890 POB 2208, Herzlia 46120, ISRAEL Cell: +972 50 5441478 [ ]Freescale Internal Use Only [ ]Freescale Confidential Proprietary Fix replaced by Shalom.Bresticker@freescale.com on Mon Oct 25 00:54:45 2004 In 4.1.14 (Concatenations): CHANGE "An operator that can be applied only to concatenations is replication, which is expressed by a concatenation preceded by a positive, non-x and non-z constant expression, enclosed together within brace characters, and which indicates a joining together of that many copies of the concatenation." TO "An operator that can be applied only to concatenations is replication, which is expressed by a concatenation preceded by a non-negative, non-x and non-z constant expression, called a replication constant, enclosed together within brace characters, and which indicates a joining together of that many copies of the concatenation." DELETE the example {0{1'b0}} // illegal At the end of 4.1.14, ADD the following: A replication operation may have a replication constant with a value of zero. This is useful in parameterized code. A replication with a zero replication constant is considered to have a size of zero and is ignored. Such a replication shall appear only within a concatenation in which at least one of the operands of the concatenation has a positive size. Examples: parameter P = 32; // The following is legal for all P from 1 to 32 assign b[31:0] = { {32-P{1'b1}}, a[P-1:0] } ; // The following is illegal for P=32, // because the zero replication appears alone within a concatenation assign c[31:0] = { {{32-P{1'b1}}}, a[P-1:0] } ; // The following is illegal for P=32 initial $displayb({32-P{1'b1}}, a[P-1:0]); |
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