aboutsummaryrefslogtreecommitdiffstats
path: root/techlibs/common/prep.cc
blob: cdd21c3b328a675070333b58f20a39acc6f66a25 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
/*
 *  yosys -- Yosys Open SYnthesis Suite
 *
 *  Copyright (C) 2012  Clifford Wolf <clifford@clifford.at>
 *
 *  Permission to use, copy, modify, and/or distribute this software for any
 *  purpose with or without fee is hereby granted, provided that the above
 *  copyright notice and this permission notice appear in all copies.
 *
 *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 */

#include "kernel/register.h"
#include "kernel/celltypes.h"
#include "kernel/rtlil.h"
#include "kernel/log.h"

USING_YOSYS_NAMESPACE
PRIVATE_NAMESPACE_BEGIN

struct PrepPass : public ScriptPass
{
	PrepPass() : ScriptPass("prep", "generic synthesis script") { }

	void help() YS_OVERRIDE
	{
		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
		log("\n");
		log("    prep [options]\n");
		log("\n");
		log("This command runs a conservative RTL synthesis. A typical application for this\n");
		log("is the preparation stage of a verification flow. This command does not operate\n");
		log("on partly selected designs.\n");
		log("\n");
		log("    -top <module>\n");
		log("        use the specified module as top module (default='top')\n");
		log("\n");
		log("    -auto-top\n");
		log("        automatically determine the top of the design hierarchy\n");
		log("\n");
		log("    -flatten\n");
		log("        flatten the design before synthesis. this will pass '-auto-top' to\n");
		log("        'hierarchy' if no top module is specified.\n");
		log("\n");
		log("    -ifx\n");
		log("        passed to 'proc'. uses verilog simulation behavior for verilog if/case\n");
		log("        undef handling. this also prevents 'wreduce' from being run.\n");
		log("\n");
		log("    -memx\n");
		log("        simulate verilog simulation behavior for out-of-bounds memory accesses\n");
		log("        using the 'memory_memx' pass.\n");
		log("\n");
		log("    -nomem\n");
		log("        do not run any of the memory_* passes\n");
		log("\n");
		log("    -rdff\n");
		log("        do not pass -nordff to 'memory_dff'. This enables merging of FFs into\n");
		log("        memory read ports.\n");
		log("\n");
		log("    -nokeepdc\n");
		log("        do not call opt_* with -keepdc\n");
		log("\n");
		log("    -run <from_label>[:<to_label>]\n");
		log("        only run the commands between the labels (see below). an empty\n");
		log("        from label is synonymous to 'begin', and empty to label is\n");
		log("        synonymous to the end of the command list.\n");
		log("\n");
		log("\n");
		log("The following commands are executed by this synthesis command:\n");
		help_script();
		log("\n");
	}

	string top_module, fsm_opts;
	bool autotop, flatten, ifxmode, memxmode, nomemmode, nokeepdc, nordff;

	void clear_flags() YS_OVERRIDE
	{
		top_module.clear();

		autotop = false;
		flatten = false;
		ifxmode = false;
		memxmode = false;
		nomemmode = false;
		nokeepdc = false;
		nordff = true;
	}

	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
	{
		string run_from, run_to;

		size_t argidx;
		for (argidx = 1; argidx < args.size(); argidx++)
		{
			if (args[argidx] == "-top" && argidx+1 < args.size()) {
				top_module = args[++argidx];
				continue;
			}
			if (args[argidx] == "-run" && argidx+1 < args.size()) {
				size_t pos = args[argidx+1].find(':');
				if (pos == std::string::npos) {
					run_from = args[++argidx];
					run_to = args[argidx];
				} else {
					run_from = args[++argidx].substr(0, pos);
					run_to = args[argidx].substr(pos+1);
				}
				continue;
			}
			if (args[argidx] == "-auto-top") {
				autotop = true;
				continue;
			}
			if (args[argidx] == "-flatten") {
				flatten = true;
				continue;
			}
			if (args[argidx] == "-ifx") {
				ifxmode = true;
				continue;
			}
			if (args[argidx] == "-memx") {
				memxmode = true;
				continue;
			}
			if (args[argidx] == "-nomem") {
				nomemmode = true;
				continue;
			}
			if (args[argidx] == "-nordff") {
				nordff = true;
				continue;
			}
			if (args[argidx] == "-rdff") {
				nordff = false;
				continue;
			}
			if (args[argidx] == "-nokeepdc") {
				nokeepdc = true;
				continue;
			}
			break;
		}
		extra_args(args, argidx, design);

		if (!design->full_selection())
			log_cmd_error("This command only operates on fully selected designs!\n");

		log_header(design, "Executing PREP pass.\n");
		log_push();

		run_script(design, run_from, run_to);

		log_pop();
	}

	void script() YS_OVERRIDE
	{

		if (check_label("begin"))
		{
			if (help_mode) {
				run("hierarchy -check [-top <top> | -auto-top]");
			} else {
				if (top_module.empty()) {
					if (flatten || autotop)
						run("hierarchy -check -auto-top");
					else
						run("hierarchy -check");
				} else
					run(stringf("hierarchy -check -top %s", top_module.c_str()));
			}
		}

		if (check_label("coarse"))
		{
			if (help_mode)
				run("proc [-ifx]");
			else
				run(ifxmode ? "proc -ifx" : "proc");
			if (help_mode || flatten)
				run("flatten", "(if -flatten)");
			run(nokeepdc ? "opt_expr" : "opt_expr -keepdc");
			run("opt_clean");
			run("check");
			run(nokeepdc ? "opt" : "opt -keepdc");
			if (!ifxmode) {
				if (help_mode)
					run("wreduce -keepdc [-memx]");
				else if (nokeepdc)
					run(memxmode ? "wreduce -memx" : "wreduce");
				else
					run(memxmode ? "wreduce -keepdc -memx" : "wreduce -keepdc");
			}
			if (!nomemmode) {
				run(string("memory_dff") + (help_mode ? " [-nordff]" : nordff ? " -nordff" : ""));
				if (help_mode || memxmode)
					run("memory_memx", "(if -memx)");
				run("opt_clean");
				run("memory_collect");
			}
			run(nokeepdc ? "opt -fast" : "opt -keepdc -fast");
		}

		if (check_label("check"))
		{
			run("stat");
			run("check");
		}
	}
} PrepPass;

PRIVATE_NAMESPACE_END
amber23.ys} \label{aber23.ys} \end{figure} The problem with this core is that it contains no dedicated reset logic. Instead the coding techniques shown in Listing~\ref{glob_arst} are used to define reset values for the global asynchronous reset in an FPGA implementation. This design can not be expressed in BLIF as it is. Instead we need to use a synthesis script that transforms this form to synchronous resets that can be expressed in BLIF. (Note that there is no problem if this coding techniques are used to model ROM, where the register is initialized using this syntax but is never updated otherwise.) \medskip Listing~\ref{aber23.ys} shows the synthesis script for the Amber23 core. In line 17 the {\tt add} command is used to add a 1-bit wide global input signal with the name {\tt globrst}. That means that an input with that name is added to each module in the design hierarchy and then all module instantiations are altered so that this new signal is connected throughout the whole design hierarchy. \begin{figure}[t!] \begin{lstlisting}[language=Verilog] reg [7:0] a = 13, b; initial b = 37; \end{lstlisting} \renewcommand{\figurename}{Listing} \caption{Implicit coding of global asynchronous resets} \label{glob_arst} \end{figure} \begin{figure}[b!] \begin{lstlisting}[language=Verilog] (* techmap_celltype = "$adff" *) module adff2dff (CLK, ARST, D, Q); parameter WIDTH = 1; parameter CLK_POLARITY = 1; parameter ARST_POLARITY = 1; parameter ARST_VALUE = 0; input CLK, ARST; input [WIDTH-1:0] D; output reg [WIDTH-1:0] Q; wire [1023:0] _TECHMAP_DO_ = "proc"; wire _TECHMAP_FAIL_ = !CLK_POLARITY || !ARST_POLARITY; always @(posedge CLK) if (ARST) Q <= ARST_VALUE; else Q <= D; endmodule \end{lstlisting} \renewcommand{\figurename}{Listing} \caption{\tt adff2dff.v} \label{adff2dff.v} \end{figure} In line 18 the {\tt proc} command is called. But in this script the signal name {\tt globrst} is passed to the command as a global reset signal for resetting the registers to their assigned initial values. Finally in line 19 the {\tt techmap} command is used to replace all instances of flip-flops with asynchronous resets with flip-flops with synchronous resets. The map file used for this is shown in Listing~\ref{adff2dff.v}. Note how the {\tt techmap\_celltype} attribute is used in line 1 to tell the techmap command which cells to replace in the design, how the {\tt \_TECHMAP\_FAIL\_} wire in lines 15 and 16 (which evaluates to a constant value) determines if the parameter set is compatible with this replacement circuit, and how the {\tt \_TECHMAP\_DO\_} wire in line 13 provides a mini synthesis-script to be used to process this cell. \begin{figure*} \begin{lstlisting}[language=C] #include <stdint.h> #include <stdbool.h> #define BITMAP_SIZE 64 #define OUTPORT 0x10000000 static uint32_t bitmap[BITMAP_SIZE/32]; static void bitmap_set(uint32_t idx) { bitmap[idx/32] |= 1 << (idx % 32); } static bool bitmap_get(uint32_t idx) { return (bitmap[idx/32] & (1 << (idx % 32))) != 0; } static void output(uint32_t val) { *((volatile uint32_t*)OUTPORT) = val; } int main() { uint32_t i, j, k; output(2); for (i = 0; i < BITMAP_SIZE; i++) { if (bitmap_get(i)) continue; output(3+2*i); for (j = 2*(3+2*i);; j += 3+2*i) { if (j%2 == 0) continue; k = (j-3)/2; if (k >= BITMAP_SIZE) break; bitmap_set(k); } } output(0); return 0; } \end{lstlisting} \renewcommand{\figurename}{Listing} \caption{Test program for the Amber23 CPU (Sieve of Eratosthenes). Compiled using GCC 4.6.3 for ARM with {\tt -Os -marm -march=armv2a -mno-thumb-interwork -ffreestanding}, linked with {\tt -{}-fix-v4bx} set and booted with a custom setup routine written in ARM assembler.} \label{sieve} \end{figure*} \section{Verification of the Amber23 CPU} The BLIF file for the Amber23 core, generated using Listings~\ref{aber23.ys} and \ref{adff2dff.v} and the version of the Amber23 RTL source that is bundled with yosys-bigsim, was verified using the test-bench from yosys-bigsim. It successfully executed the program shown in Listing~\ref{sieve} in the test-bench. For simulation the BLIF file was converted back to Verilog using ABC \cite{ABC}. So this test includes the successful transformation of the BLIF file into ABC's internal format as well. The only thing left to write about the simulation itself is that it probably was one of the most energy inefficient and time consuming ways of successfully calculating the first 31 primes the author has ever conducted. \section{Limitations} At the time of this writing Yosys does not support multi-dimensional memories, does not support writing to individual bits of array elements, does not support initialization of arrays with {\tt \$readmemb} and {\tt \$readmemh}, and has only limited support for tristate logic, to name just a few limitations. That being said, Yosys can synthesize an overwhelming majority of real-world Verilog RTL code. The remaining cases can usually be modified to be compatible with Yosys quite easily. The various designs in yosys-bigsim are a good place to look for examples of what is within the capabilities of Yosys. \section{Conclusion} Yosys is a feature-rich Verilog-2005 synthesis tool. It has many uses, but one is to provide an easy gateway from high-level Verilog code to low-level logic circuits. The command line option {\tt -S} can be used to quickly synthesize Verilog code to BLIF files without a hassle. With custom synthesis scripts it becomes possible to easily perform high-level optimizations, such as re-encoding FSMs. In some extreme cases, such as the Amber23 ARMv2 CPU, the more advanced Yosys features can be used to change a design to fit a certain need without actually touching the RTL code. \begin{thebibliography}{9} \bibitem{yosys} Clifford Wolf. The Yosys Open SYnthesis Suite. \\ \url{http://www.clifford.at/yosys/} \bibitem{bigsim} yosys-bigsim, a collection of real-world Verilog designs for regression testing purposes. \\ \url{https://github.com/cliffordwolf/yosys-bigsim} \bibitem{navre} Sebastien Bourdeauducq. Navr\'e AVR clone (8-bit RISC). \\ \url{http://opencores.org/project,navre} \bibitem{amber} Conor Santifort. Amber ARM-compatible core. \\ \url{http://opencores.org/project,amber} \bibitem{ABC} Berkeley Logic Synthesis and Verification Group. ABC: A System for Sequential Synthesis and Verification. \\ \url{http://www.eecs.berkeley.edu/~alanmi/abc/} \bibitem{blif} Berkeley Logic Interchange Format (BLIF) \\ \url{http://vlsi.colorado.edu/~vis/blif.ps} \end{thebibliography} \end{document}