array signal in process problem

[jin]

I need to generate a set of array signal from a vector, see below:

input:
config_clock : in std_logic_vector(24 downto 1);

internal signal array:
type chain_array is array (24 downto 1) of std_logic_vector(24 downto
1);
signal clock_chain_mask : chain_array;

the process is to generate 24*24 mask signal, if I define 24 signal
like:
signal clock_chain_mask_1 : std_logic_vector(24 downto 1);
signal clock_chain_mask_2 : std_logic_vector(24 downto 1);
....
....
signal clock_chain_mask_24 : std_logic_vector(24 downto 1);

then call 24 processes like:
U1: process ( config_clock(1))
variable j; --j is valid from 1 to 24
...
... clock_chain_mask_1(j) <= '1';
end process U1;

U2: process ( config_clock(2))
variable j;
...
... clock_chain_mask_1(j) <= '1';
end process U2;

This works fine. If I change data structure to array, like:
U1: process ( config_clock(1))
variable j;
...
... clock_chain_mask(j)(1) <= '1';
end process U1;

U2: process ( config_clock(2))
variable j;
...
... clock_chain_mask(j)(2) <= '1';
end process U2;

the clock_chain_mask array cannot ouput any signal. I am wondering if
the array signal can be assigned in process like this way. Thanks.

 

[Pieter Hulshoff]

then call 24 processes like:
U1: process ( config_clock(1))
variable j; --j is valid from 1 to 24
...
... clock_chain_mask_1(j) <= '1';
end process U1;

U2: process ( config_clock(2))
variable j;
...
... clock_chain_mask_1(j) <= '1';

I presume you meant clock_chain_mask_2(j) here?

This works fine. If I change data structure to array, like:
U1: process ( config_clock(1))
variable j;
...
... clock_chain_mask(j)(1) <= '1';
end process U1;

U2: process ( config_clock(2))
variable j;
...
... clock_chain_mask(j)(2) <= '1';
end process U2;
the clock_chain_mask array cannot ouput any signal. I am wondering if
the array signal can be assigned in process like this way. Thanks.

Signals are considered one entity. This means that if you write 1 element of
an array, you implicitely write the other elements with their current
value. Since you cannot write to one signal from multiple processes, you
cannot do this with elements of an array either. That's why your first
example has no problems, and the second example does.

Regards,

Pieter Hulshoff