From f76f76c44520e1fc0d15456b8c5eb929f8495b5b Mon Sep 17 00:00:00 2001
From: Yann Herklotz <git@yannherklotz.com>
Date: Tue, 30 Jun 2020 23:31:09 +0100
Subject: Adding more comments

---
 verilog.tex | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

(limited to 'verilog.tex')

diff --git a/verilog.tex b/verilog.tex
index 67f2f4e..f40baf5 100644
--- a/verilog.tex
+++ b/verilog.tex
@@ -2,20 +2,20 @@
 
 Verilog is a hardware description language commonly used to design hardware.  A Verilog design can then be synthesised into more basic logic which describes how different gates connect to each other, called a netlist.  This representation can then be put onto either a field-programmable gate array (FPGA) or turned into an application-specific integrated circuit (ASPIC) to implement the design that was described in Verilog.  The Verilog standard is quite large though, and not all Verilog features are needed to be able to describe hardware.  Many Verilog features are only useful for simulation and do not affect the actual hardware itself, which means that these features do not have to be modelled in the semantics.  In addition to that, as the HLS algorithm dictates which Verilog constructs are generated, meaning the Verilog subset that has to be modelled by the semantics can be reduced even further to only support the constructs that are needed.  Only supporting a smaller subset in the semantics also means that there is less chance that the standard is misunderstood, and that the semantics actually model how the Verilog is simulated.
 
-The Verilog semantics are based on the semantics proposed by \citet{loow19_verif_compil_verif_proces}, which were used to create a formal translation from HOL logic into a Verilog circuit.  These semantics are quite practical as they restrict themselves to a small subset of Verilog, which can nonetheless be used to model all hardware constructs one would want to design.  The main syntax for the Verilog subset is the following: \JW{This verilog syntax looks weird to me. I didn't think there was a `then' keyword, for instance. Perhaps you're aiming more at some sort of abstracted syntax of Verilog? What does the semicolon on its own mean? Some sort of skip statement? The case statement looks weird too -- how do you get multiple cases in a single switch statement, and where is the default case? }\YH{I think I have fixed most cases, yes the single semicolon is a skip statement, should I make that more obvious by naming it? } \JW{It still looks a bit funny to me -- a bit of a halfway-house between `proper' Verilog syntax and `abstract' Verilog syntax. E.g. the way `begin...end' blocks contain exactly two statements, or the way that you get an erroneous double semicolon by combining the `begin...end' rule with the `e=e;' rule. People who are very familiar with C-like syntax will know that this isn't quite right... but then again, it doesn't really matter whether you handle the full syntax, because you only have to pretty-print a subset of it. So, why not stick here with a slightly abstracted Verilog syntax? It would make the operational semantics easier to read, for instance. Basically like you had it before, but explicitly labelled as a simplified syntax, so readers don't get confused!}
+The Verilog semantics are based on the semantics proposed by \citet{loow19_verif_compil_verif_proces}, which were used to create a formal translation from HOL logic into a Verilog circuit.  These semantics are quite practical as they restrict themselves to a small subset of Verilog, which can nonetheless be used to model all hardware constructs one would want to design.  The main syntax for the Verilog subset is the following: \JW{This verilog syntax looks weird to me. I didn't think there was a `then' keyword, for instance. Perhaps you're aiming more at some sort of abstracted syntax of Verilog? What does the semicolon on its own mean? Some sort of skip statement? The case statement looks weird too -- how do you get multiple cases in a single switch statement, and where is the default case? }\YH{I think I have fixed most cases, yes the single semicolon is a skip statement, should I make that more obvious by naming it? } \JW{It still looks a bit funny to me -- a bit of a halfway-house between `proper' Verilog syntax and `abstract' Verilog syntax. E.g. the way `begin...end' blocks contain exactly two statements, or the way that you get an erroneous double semicolon by combining the `begin...end' rule with the `e=e;' rule. People who are very familiar with C-like syntax will know that this isn't quite right... but then again, it doesn't really matter whether you handle the full syntax, because you only have to pretty-print a subset of it. So, why not stick here with a slightly abstracted Verilog syntax? It would make the operational semantics easier to read, for instance. Basically like you had it before, but explicitly labelled as a simplified syntax, so readers don't get confused!}\YH{Yeah, the syntax is a bit funny, mostly because this is actually how it is also encoded in Coq.  The main weird rule is the Seq rule, basically because it actually doesn't have a semicolon in between and no begin and end block, but it looks a bit strange to just put two $s$ next to each other.  We therefore don't really have begin and end blocks, and basically glue them to each statement instead, so in our semantics, the if statement actually looks like: if $e$ begin $s$ end else begin $s$ end, but it gets very verbose for case statements.  I got rid of the sequence for now, so maybe this is better, but this is nearly exactly how we actually encode it.}
 
 \begin{align*}
   v\quad ::=&\; \mathit{sz} \yhkeyword{'d} n\\
   \textit{op}\quad ::=&\; \yhkeyword{+ } | \yhkeywordsp{- } | \yhkeywordsp{* } \cdots \\
   e\quad ::=&\; v\;\; |\;\; x\;\; |\;\; e \yhkeyword{[} e \yhkeyword{]}\;\; |\;\; e\ \mathit{op}\ e\;\; |\;\; \yhkeyword{!} e\;\; |\;\; \yhkeyword{\textasciitilde} e\;\; |\;\; e \yhkeywordsp{? } e \yhkeywordsp{: } e\\
-  s\quad ::=&\; \yhkeyword{begin } s \yhkeyword{; } s \yhkeywordsp{end } |\ \epsilon\\[-2pt]
+  s\quad ::=&\; s s |\ \epsilon\\[-2pt]
   |&\; \yhkeyword{if } e\ s \yhkeywordsp{else } s\\[-2pt]
   |&\; \yhkeyword{case (} e \yhkeyword{) } e : s\ \{\ e : s\ \}\ [\ \yhkeyword{default} : \textit{def}\ ] \yhkeywordsp{endcase}\\[-2pt]
   |&\; e = e \yhkeyword{;}\\[-2pt]
   |&\; e \Leftarrow e \yhkeyword{;}\\
   d\quad ::=&\; \yhkeyword{[n-1:0] } r\ |\ \yhkeyword{[n-1:0] } r \yhkeywordsp{[m-1:0]}\\
   m\quad ::=&\; \yhkeyword{reg } d \yhkeyword{;}\ |\ \yhkeyword{input wire } d \yhkeyword{;}\ |\ \yhkeyword{output reg } d \yhkeyword{;}\\
-|&\; \yhkeywordsp{always @(posedge clk) begin } s \yhkeywordsp{end}\\
+|&\; \yhkeywordsp{always @(posedge clk) } s \\
   m \text{ list}\quad ::=&\; \{ m \}
 \end{align*}
 
@@ -49,17 +49,17 @@ The two main evaluation functions are then \textit{erun}, which takes in the cur
 %
   \inferrule[CondTrue]{\textit{erun}\ \Gamma_{0}\ c\ v_{c} \\ \yhfunction{valToB}\ v_{c} = \yhconstant{true} \\ \textit{srun}\ \sigma_{0}\ \textit{st}\ \sigma_{1}}{\textit{srun}\ \sigma_{0}\ (\yhkeyword{if } c\ \textit{st} \yhkeywordsp{else } \textit{sf})\ \sigma_{1}}\\
 %
-  \inferrule[CondFalse]{\textit{erun}\ \Gamma_{0}\ c\ v_{c} \\ \yhfunction{valToB}\ v_{c} = \yhconstant{false} \\ \textit{srun}\ \sigma_{0}\ \textit{sf}\ \sigma_{1}}{\textit{srun}\ \sigma_{0}\ (\yhkeyword{if } c\ \textit{st} \yhkeywordsp{else } \textit{sf})\ \sigma_{1}}\\
+  \inferrule[CondFalse]{\textit{erun}\ \Gamma_{0}\ c\ v_{\rm c} \\ \yhfunction{valToB}\ v_{\rm c} = \yhconstant{false} \\ \textit{srun}\ \sigma_{0}\ \textit{sf}\ \sigma_{1}}{\textit{srun}\ \sigma_{0}\ (\yhkeyword{if } c\ \textit{st} \yhkeywordsp{else } \textit{sf})\ \sigma_{1}}\\
 %
-  \inferrule[CaseNoMatch]{\textit{srun}\ \sigma_{0}\ (\yhkeyword{case}\ e\ cs\ \textit{def})\ \sigma_{1} \\ \textit{erun}\  \Gamma_{0}\ me\ mve \\ \textit{erun}\  \Gamma_{0}\ e\ ve \\ mve \neq ve}{\textit{srun}\  \sigma_{0}\ (\yhkeyword{case (} e \yhkeyword{) } (me : sc) :: cs) \yhkeywordsp{default} : \textit{def} \yhkeywordsp{endcase})\ \sigma_{1}}\\
+  \inferrule[CaseNoMatch]{\textit{srun}\ \sigma_{0}\ (\yhkeyword{case}\ e\ cs\ \textit{def})\ \sigma_{1} \\ \textit{erun}\  \Gamma_{0}\ me\ mve \\ \textit{erun}\  \Gamma_{0}\ e\ ve \\ mve \neq ve}{\textit{srun}\  \sigma_{0}\ (\yhkeyword{case (} e \yhkeyword{) } ((me : sc) :: cs) \yhkeywordsp{default} : \textit{def} \yhkeywordsp{endcase})\ \sigma_{1}}\\
 %
-  \inferrule[CaseMatch]{\textit{srun}\  \sigma_{0}\ sc\ \sigma_{1} \\ \textit{erun}\  \Gamma_{0}\ e\ ve \\ \textit{erun}\  \Gamma_{0}\ me\ mve \\ mve = ve}{\textit{srun}\  \sigma_{0}\ (\yhkeyword{case (} e \yhkeyword{) } (me : sc) :: cs) \yhkeywordsp{default} : \textit{def} \yhkeywordsp{endcase})\ \sigma_{1}}\\
+  \inferrule[CaseMatch]{\textit{srun}\  \sigma_{0}\ sc\ \sigma_{1} \\ \textit{erun}\  \Gamma_{0}\ e\ ve \\ \textit{erun}\  \Gamma_{0}\ me\ mve \\ mve = ve}{\textit{srun}\  \sigma_{0}\ (\yhkeyword{case (} e \yhkeyword{) } ((me : sc) :: cs) \yhkeywordsp{default} : \textit{def} \yhkeywordsp{endcase})\ \sigma_{1}}\\
 %
   \inferrule[CaseDefault]{\textit{srun}\  \sigma_{0}\ s\ \sigma_{1}}{\textit{srun}\  \sigma_{0}\ (\yhkeyword{case (} e \yhkeyword{) } [] \yhkeywordsp{default} : (\yhkeyword{Some}\ s) \yhkeywordsp{endcase})\ \sigma_{1}}\\
 %
-  \inferrule[Blocking Reg]{\yhfunction{name}\ \textit{lhs} = \yhconstant{OK}\ n \\ \textit{erun}\  \Gamma_{r}\ \Gamma_{a}\ \textit{rhs}\ v_{\textit{rhs}}}{\textit{srun}\  (\Gamma_{r},\Gamma_{a},\Delta_{r},\Delta_{a})\ (\textit{lhs} = \textit{rhs})\ (\Gamma_{r} [n \mapsto v_{\textit{rhs}}], \Gamma_{a}, \Delta_{r}, \Delta_{a})}\\
+  \inferrule[Blocking Reg]{\yhfunction{name}\ \textit{lhs} = \yhconstant{OK}\ n \\ \textit{erun}\  \Gamma_{\rm r}\ \Gamma_{\rm a}\ \textit{rhs}\ v_{\rm rhs}}{\textit{srun}\  (\Gamma_{\rm r},\Gamma_{\rm a},\Delta_{\rm r},\Delta_{\rm a})\ (\textit{lhs} = \textit{rhs})\ (\Gamma_{\rm r} [n \mapsto v_{\rm rhs}], \Gamma_{\rm a}, \Delta_{\rm r}, \Delta_{\rm a})}\\
 %
-  \inferrule[Nonblocking Reg]{\yhfunction{name}\ \textit{lhs} = \yhconstant{OK}\ n \\ \textit{erun}\  \Gamma\ \textit{rhs}\ v_{\textit{rhs}}}{\textit{srun}\  (\Gamma_{r}, \Gamma_{a}, \Delta_{r}, \Delta_{a})\ (\textit{lhs} \Leftarrow \textit{rhs})\ (\Gamma_{r}, \Gamma_{a}, \Delta_{r} [n \mapsto v_{\textit{rhs}}], \Delta_{a})}
+  \inferrule[Nonblocking Reg]{\yhfunction{name}\ \textit{lhs} = \yhconstant{OK}\ n \\ \textit{erun}\  \Gamma\ \textit{rhs}\ v_{\textit{rhs}}}{\textit{srun}\  (\Gamma_{\rm r}, \Gamma_{\rm a}, \Delta_{\rm r}, \Delta_{a})\ (\textit{lhs} \Leftarrow \textit{rhs})\ (\Gamma_{\rm r}, \Gamma_{\rm a}, \Delta_{\rm r} [n \mapsto v_{\rm rhs}], \Delta_{\rm a})}
 %
 %  \inferrule[Blocking Array]{\yhkeyword{name}\ \textit{lhs} = \yhkeyword{OK}\ n \\ \textit{erun}\  \Gamma_{r}\ \Gamma_{a}\ \textit{rhs}\ v_{\textit{rhs}}}{\textit{srun}\  (\Gamma_{r},\Gamma_{a},\Delta_{r},\Delta_{a})\ (\textit{lhs} = \textit{rhs})\ (\Gamma_{r} // \{n \rightarrow v_{\textit{rhs}}\}, \Gamma_{a}, \Delta_{r}, \Delta_{a})}\\
 %
-- 
cgit 

