Proper reset generation

m-labs · Dec 16, 2011 · 411e1af · 411e1af
1 parent 738b45d
commit 411e1af
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Showing 6 changed files with 103 additions and 11 deletions.
diff --git a/build.py b/build.py
@@ -10,6 +10,7 @@ def add_core_dir(d):
 def add_core_files(d, files):
 	for f in files:
 		verilog_sources.append(os.path.join("verilog", d, f))
+add_core_dir("m1reset")
 add_core_files("lm32", ["lm32_cpu.v", "lm32_instruction_unit.v", "lm32_decoder.v",
 	"lm32_load_store_unit.v", "lm32_adder.v", "lm32_addsub.v", "lm32_logic_op.v",
 	"lm32_shifter.v", "lm32_multiplier_spartan6.v", "lm32_mc_arithmetic.v",

diff --git a/constraints.py b/constraints.py
@@ -1,4 +1,4 @@
-def get(ns, norflash0, uart0):
+def get(ns, reset0, norflash0, uart0):
 	constraints = []
 	def add(signal, pin, vec=-1, iostandard="LVCMOS33", extra=""):
 		constraints.append((ns.get_name(signal), vec, pin, iostandard, extra))
@@ -8,6 +8,11 @@ def add_vec(signal, pins, iostandard="LVCMOS33", extra=""):
 			add(signal, p, i, iostandard, extra)
 			i += 1
 
+	add(reset0.trigger_reset, "AA4")
+	add(reset0.ac97_rst_n, "D6")
+	add(reset0.videoin_rst_n, "W17")
+	add(reset0.flash_rst_n, "P22", extra="SLEW = FAST | DRIVE = 8")
+
 	add_vec(norflash0.adr, ["L22", "L20", "K22", "K21", "J19", "H20", "F22",
 		"F21", "K17", "J17", "E22", "E20", "H18", "H19", "F20",
 		"G19", "C22", "C20", "D22", "D21", "F19", "F18", "D20", "D19"],
@@ -18,7 +23,6 @@ def add_vec(signal, pins, iostandard="LVCMOS33", extra=""):
 	add(norflash0.oe_n, "M22", extra="SLEW = FAST | DRIVE = 8")
 	add(norflash0.we_n, "N20", extra="SLEW = FAST | DRIVE = 8")
 	add(norflash0.ce_n, "M21", extra="SLEW = FAST | DRIVE = 8")
-	add(norflash0.rst_n, "P22", extra="SLEW = FAST | DRIVE = 8")
 
 	add(uart0.tx, "L17", extra="SLEW = SLOW")
 	add(uart0.rx, "K18", extra="PULLUP")
@@ -38,8 +42,6 @@ def add_vec(signal, pins, iostandard="LVCMOS33", extra=""):
 NET "sys_clk" LOC = AB11 | IOSTANDARD = LVCMOS33;
 NET "sys_clk" TNM_NET = "GRPclk50";
 TIMESPEC "TSclk50" = PERIOD "GRPclk50" 20 ns HIGH 50%;
-
-NET "sys_rst" LOC = AA4 | IOSTANDARD = LVCMOS33;
 	"""
 
 	return r
diff --git a/milkymist/m1reset/__init__.py b/milkymist/m1reset/__init__.py
@@ -0,0 +1,23 @@
+from functools import partial
+
+from migen.fhdl.structure import *
+
+class Inst:
+	def __init__(self):
+		d = partial(declare_signal, self)
+		d("trigger_reset")
+		d("sys_rst")
+		d("ac97_rst_n")
+		d("videoin_rst_n")
+		d("flash_rst_n")
+		self._inst = Instance("m1reset",
+			[("sys_rst", self.sys_rst),
+			("ac97_rst_n", self.ac97_rst_n),
+			("videoin_rst_n", self.videoin_rst_n),
+			("flash_rst_n", self.flash_rst_n)],
+			[("trigger_reset", self.trigger_reset)],
+			clkport="sys_clk")
+
+	def get_fragment(self):
+		return Fragment(instances=[self._inst],
+			pads={self.ac97_rst_n, self.videoin_rst_n, self.flash_rst_n})
diff --git a/milkymist/norflash/__init__.py b/milkymist/norflash/__init__.py
@@ -13,7 +13,6 @@ def __init__(self, adr_width, rd_timing):
 		d("oe_n")
 		d("we_n")
 		d("ce_n")
-		d("rst_n")
 		self.timeline = timeline.Inst(self.bus.cyc_i & self.bus.stb_i,
 			[(0, [self.adr.eq(Cat(0, self.bus.adr_i[2:adr_width]))]),
 			(rd_timing, [
@@ -27,6 +26,6 @@ def __init__(self, adr_width, rd_timing):
 
 	def get_fragment(self):
 		comb = [self.oe_n.eq(0), self.we_n.eq(1),
-			self.ce_n.eq(0), self.rst_n.eq(1)]
-		return Fragment(comb, pads={self.adr, self.d, self.oe_n, self.we_n, self.ce_n, self.rst_n}) \
+			self.ce_n.eq(0)]
+		return Fragment(comb, pads={self.adr, self.d, self.oe_n, self.we_n, self.ce_n}) \
 			+ self.timeline.get_fragment()
diff --git a/top.py b/top.py
@@ -1,10 +1,13 @@
+from migen.fhdl.structure import *
 from migen.fhdl import convtools, verilog, autofragment
 from migen.bus import wishbone, csr, wishbone2csr
 
-from milkymist import lm32, norflash, uart
+from milkymist import m1reset, lm32, norflash, uart
 import constraints
 
 def get():
+	reset0 = m1reset.Inst()
+
 	cpu0 = lm32.Inst()
 	norflash0 = norflash.Inst(25, 12)
 	wishbone2csr0 = wishbone2csr.Inst()
@@ -16,8 +19,10 @@ def get():
 	uart0 = uart.Inst(0, 50*1000*1000, baud=115200)
 	csrcon0 = csr.Interconnect(wishbone2csr0.csr, [uart0.bus])
 
-	frag = autofragment.from_local()
+	frag = autofragment.from_local() + Fragment(pads={reset0.trigger_reset})
 	vns = convtools.Namespace()
-	src_verilog = verilog.Convert(frag, name="soc", ns=vns)
-	src_ucf = constraints.get(vns, norflash0, uart0)
+	src_verilog = verilog.Convert(frag, name="soc",
+		rst_signal=reset0.sys_rst,
+		ns=vns)
+	src_ucf = constraints.get(vns, reset0, norflash0, uart0)
 	return (src_verilog, src_ucf)
diff --git a/verilog/m1reset/m1reset.v b/verilog/m1reset/m1reset.v
@@ -0,0 +1,62 @@
+/*
+ * Milkymist-NG SoC
+ * Copyright (C) 2007, 2008, 2009, 2010, 2011 Sebastien Bourdeauducq
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+module m1reset(
+	input sys_clk,
+	input trigger_reset,
+
+	output reg sys_rst,
+	output ac97_rst_n,
+	output videoin_rst_n,
+	output flash_rst_n
+);
+
+reg [19:0] rst_debounce;
+initial rst_debounce <= 20'hFFFFF;
+initial sys_rst <= 1'b1;
+always @(posedge sys_clk) begin
+	if(trigger_reset)
+		rst_debounce <= 20'hFFFFF;
+	else if(rst_debounce != 20'd0)
+		rst_debounce <= rst_debounce - 20'd1;
+	sys_rst <= rst_debounce != 20'd0;
+end
+
+assign ac97_rst_n = ~sys_rst;
+assign videoin_rst_n = ~sys_rst;
+
+/*
+ * We must release the Flash reset before the system reset
+ * because the Flash needs some time to come out of reset
+ * and the CPU begins fetching instructions from it
+ * as soon as the system reset is released.
+ * From datasheet, minimum reset pulse width is 100ns
+ * and reset-to-read time is 150ns.
+ */
+
+reg [7:0] flash_rstcounter;
+initial flash_rstcounter <= 8'd0;
+always @(posedge sys_clk) begin
+	if(trigger_reset)
+		flash_rstcounter <= 8'd0;
+	else if(~flash_rstcounter[7])
+		flash_rstcounter <= flash_rstcounter + 8'd1;
+end
+
+assign flash_rst_n = flash_rstcounter[7];
+
+endmodule