i have alu that has a 32 bit input, the multiplier outputs 64 bits, but i need the result of the multiplction to be in 32 bit so i could load it into a 32 bit register. dose anyone has any idea how can convert the 64 bit output to 32bit?
slim_pga wrote: > dose anyone has any idea how can convert the 64 bit output to 32bit? The usual ways are to truncate the first or the last 32 bits of the result. What ist the highest number that will show up in the 64bit result? Will it fit in a 32 bit number? E.g. when the highest number to be calculated is 100000 x 100000 then simply truncate the first 32 bits, because they will hold no necessary information...
i have a 32bit signale called multi_out. and a mux that inputs 32bit as well. the thing is, that the multi_out is connected between my multiplier output ans mux input. the mux and evrything else in the system works on 32 bit. here is the last part of the code:
1 | signal add_sub_out : std_logic_vector (31 downto 0); |
2 | signal multi_out : std_logic_vector (63 downto 0); |
3 | begin
|
4 | alu_add_sub : adder_subtractor port map (leftin,rightin,opcode(0),negative,add_sub_out); |
5 | alu_multi : Multiplier_VHDL port map (leftin,rightin,multi_out); |
6 | mux : alu_mux port map (add_sub_out,multi_out (31 downto 0),opcode(1),res); |
7 | end struc; |
in the one to last line i tried to connect the multi_out signal to the first 32 bists of the multiplier output. (my profesor said its cool to do that for our project) but it dosent work.
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Edited by Moderator
slim_pga wrote: > but it dosent work. How did you find that out? > in the one to last line i tried to connect the multi_out signal to the > first 32 bists of the multiplier output. The "first" bits (starting from left like reading a text) are "63 downto 32". What you do is to use the 32 lower bits and that is what I suggested. In reality this assignmet by location is not a good idea:
1 | mux : alu_mux port map (add_sub_out,multi_out (31 downto 0),opcode(1),res); |
Its just laziness during writing...
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Edited by Moderator
Lothar M. wrote: > In reality this assignmet by location is not a good idea:mux : alu_mux > port map (add_sub_out,multi_out (31 downto 0),opcode(1),res); > Its just laziness during writing... How would you write it then?
I would use explicit declared assignments like that http://www.lothar-miller.de/s9y/archives/57-Sinusausgabe-mit-PWM.html But that's (hopefully) not the problem here...
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