问题描述
我目前正在使用Perl解析来自RS232串行端口的输入命令序列。 我尝试使用状态机，它的预期行为是： （1）从串口接收一系列字节； （2）状态机使用字节作为输入，并跳转到适当的状态。
我想出了一个简化的Perl演示代码（在下面发布），但是遇到了一个问题： 当代码输入“ while（1）{}”时，它会卡在这里，并且无法退出。 因此， $ din字节序列分配被“ while（1）{}”阻止，并且对状态机不可见。 因此，FSM处于“ INIT”状态，根本不跳。
我认为这应该是Perl编码中非常简单的入门级实践， 但是通过Google搜索并不能帮到我太多。 谁能帮我这个？ 提前谢谢〜
...
my %next_state = (
"INIT" => sub{
$din eq "AA" and return "HEADER0" ;
return "INIT" ;
},"HEADER0" => sub{
$din eq "99" and return "HEADER1" ;
return "INIT" ;
},...
);
# Set state machine's initial state.
my $cur_state = "INIT" ;
# Integer for debugging purpose.
my $itgi = 0;
# Run the state machine.
while(1){
$cur_state = $next_state{$cur_state}();
print "$itgi,will jump to: $cur_state\n\n";
$itgi++;
}
# Send in input byte sequence,which simulates
# incoming bytes from RS-232 COM port:
$din = "AA" ;
sleep(1) ;
...
========== 2020.10.09 22:10更新==========
感谢@ikegami的帮助， 调试工作，现在我可以得到一点甜美的Perl状态 机器启动并运行，代码如下。
但是，它仍然存在一个问题，即：
输入字节序列（即@seq）必须为非0x00值； 如果我在命令序列中放入0x00，则FSM 遇到0x00时将退出。
这是为什么？代码使用“ $ cur_byte> = 0 ”，在我看来 应该能够处理0x00，就像处理非零值一样。
为什么0x00将状态机拉出运行状态？
use strict ;
use warnings ;
# input to the state machine
my $din ;
#---------------------------------------------------------------------
# FSM's state table.
#---------------------------------------------------------------------
# Expected input sequence is:
# AA 99 00 01 ....
# In which:
# (1) Fixed pattern "AA" and "99" are two bytes of header,# (2) Following bytes are uart ID,etc.
my %next_state = (
"INIT" => sub{
# If receives "AA" from input,# then jumpt to "HEADER0" state:
$din eq "AA" and return "HEADER0" ;
# Otherwise just stay here:
return "INIT" ;
},"HEADER0" => sub{
# If receives "99" from input,# then proceed to "HEADER1" state:
$din eq "99" and return "HEADER1" ;
# Otherwise,return to initial state:
return "INIT" ;
},"HEADER1" => sub{
# Capture first byte of uart ID:
return "UARTID0";
},"UARTID0" => sub{
# Capture second byte of uart ID:
return "UARTID1";
},"UARTID1" => sub{
# Capture second byte of uart ID:
return "FINISHED";
},"FINISHED" => sub{
return "INIT";
},);
#---------------------------------------------------------------------
# Set state machine's initial state.
#---------------------------------------------------------------------
my $cur_state = "INIT" ;
#---------------------------------------------------------------------
# Send in command sequence
#---------------------------------------------------------------------
my @seq = (-1,0xAA,-1,0x99,0x06,0x07,0x08,0x09,0x0a,0x0b,0x0c,0x0d
);
sub get_next_byte {
while (@seq) { #(A)
my $cur_byte = shift(@seq);
return $cur_byte if $cur_byte >= 0;
#
sleep(-$cur_byte);
}
return (); #(B)
}
#---------------------------------------------------------------------
# Run the state machine.
#---------------------------------------------------------------------
# Integer for debugging purpose.
my $itgi = 0;
while( $din = get_next_byte() ){ #(C)
$din = sprintf("%02X",$din);
$cur_state = $next_state{$cur_state}();
print "-- Iteration $itgi,will jump to: $cur_state\n";
$itgi++;
}
print "-- Program finish.\n";
解决方法
您无需更改$din即可进入循环。您需要类似
# Run the state machine.
while ( my ($din) = get_next_byte() ) {
$din = sprintf("%02X",$din);
$cur_state = $next_state{$cur_state}();
print "$itgi,will jump to: $cur_state\n\n";
$itgi++;
}
出于测试目的，您可以使用
my @seq = (-1,0xAA,-1,0x99);
sub get_next_byte {
while (@seq) {
my $next = shift(@seq);
return $next if $next >= 0;
sleep(-$next);
}
return ();
}
感谢@zdim和@ikegami的帮助，现在我终于完全完成了该程序。如果有人可能有相同的问题，我将在下面发布我的工作代码。
以下代码受zdim启发：
try{
System.out.printf("Hey,%s. How old are you?: ",name);
age = input.nextInt();
} catch (InputMismatchException e){
System.out.printf("Agh! Sorry %s. We were expecting a number made up of digits between 0-9. Try again for us? \n How old are you?: ",name);
input.nextLine();
age = input.nextInt();
}
下面的dode受到ikegami的启发，请注意use strict ;
use warnings ;
# input to the state machine
my $din ;
# FSM's state table.
# Expected input sequence is:
# AA 99 00 01 ....
# In which:
# "AA" and "99" are two bytes of header,# "00" and "01" are two bytes of uart ID.
my %next_state = (
"INIT" => sub{
# If receives "AA" from input,# then jumpt to "HEADER0" state:
$din eq "AA" and return "HEADER0" ;
# Otherwise just stay here:
return "INIT" ;
},"HEADER0" => sub{
# If receives "99" from input,# then proceed to "HEADER1" state:
$din eq "99" and return "HEADER1" ;
# Otherwise,return to initial state:
return "INIT" ;
},"HEADER1" => sub{
# Capture first byte of uart ID:
return "UARTID0";
},"UARTID0" => sub{
# Capture second byte of uart ID:
return "UARTID1";
},# "UARTID1" => sub{
# return "FINISHED";
# },"FINISHED" => sub{
return "INIT";
},);
# Set state machine's initial state.
my $cur_state = "INIT" ;
# Integer for debugging purpose.
my $itgi = 0;
# Run the state machine.
while($din = <>){
chomp $din ;
$cur_state = $next_state{$cur_state}();
print "$itgi,will jump to: $cur_state\n\n";
$itgi++;
}
# Send in input bytes:
$din = "AA" ;
sleep(1) ;
$din = "99" ;
sleep(1) ;
和简单的($din)之间的区别，不带括号：使用括号，我们得出TRUE或FALSE结果；不带括号的话，我们得到的实际元素值为$din，如果该值为@seq，则0x00将变为while并退出。
while(0)