Chisel始终生成感应列表中只有时钟的块:
always @posedge(clk) begin
[...]
end
是否可以将模块配置为使用异步重置并生成这样的始终块?
always @(posedge clk or posedge reset) begin
[...]
end
看起来在Chisel中这样做的方法是使用同步重置:
always @posedge(clk) begin
if (reset) begin
[...]
end
else
[...]
end
end
有关该主题的更多讨论:https://groups.google.com/forum/#!主题/凿用户/4cc4SyB5mk8
自Chisel 3.2.0以来,支持同步、异步和抽象重置类型。根据明确指定或推断的重置类型,您将获得规范的同步或异步Verilog输出。
为了更充分地展示这一点,考虑以下MultiIOModule
,它有三个重置:
- 具有抽象重置类型的隐式
reset
输入(这是"抽象重置") - 具有
Bool
类型的显式syncReset
输入(这是"同步重置") - 具有
AsyncReset
类型的显式asyncReset
输入(这是"异步重置")
使用withReset
,特定的复位连接可以用于设计中的不同寄存器:
import chisel3._
import chisel3.stage.ChiselStage
class Foo extends MultiIOModule {
val syncReset = IO(Input(Bool() ))
val asyncReset = IO(Input(AsyncReset()))
val in = IO(Input( Bool()))
val outAbstract = IO(Output(Bool()))
val outSync = IO(Output(Bool()))
val outAsync = IO(Output(Bool()))
val regAbstract = RegNext(in, init=0.U)
val regSync = withReset(syncReset) { RegNext(in, init=0.U) }
val regAsync = withReset(asyncReset) { RegNext(in, init=0.U) }
outAbstract := regAbstract
outSync := regSync
outAsync := regAsync
}
当使用(new ChiselStage).emitVerilog(new Foo)
:进行编译时,这将生成以下Verilog
module Foo(
input clock,
input reset,
input syncReset,
input asyncReset,
input in,
output outAbstract,
output outSync,
output outAsync
);
reg regAbstract;
reg regSync;
reg regAsync;
assign outAbstract = regAbstract;
assign outSync = regSync;
assign outAsync = regAsync;
always @(posedge clock) begin
if (reset) begin
regAbstract <= 1'h0;
end else begin
regAbstract <= in;
end
if (syncReset) begin
regSync <= 1'h0;
end else begin
regSync <= in;
end
end
always @(posedge clock or posedge asyncReset) begin
if (asyncReset) begin
regAsync <= 1'h0;
end else begin
regAsync <= in;
end
end
endmodule
注意:在Chisel 3.2中,顶级抽象重置将始终设置为同步重置。在Chisel 3.3.0中添加了两个性状:RequireSyncReset
和RequireAsyncReset
。这些可用于将连接到regAbstract
的寄存器的重置类型从同步更改为异步。用(new ChiselStage).emitVerilog(new Foo with RequireAsyncReset)
重新编译设计,将regAbstract
逻辑更改为
always @(posedge clock or posedge reset) begin
if (reset) begin
regAbstract <= 1'h0;
end else begin
regAbstract <= in;
end
end
欲了解更多信息,Chisel网站有更多重置信息。