On 23/12/2010 12:59, Jean-Christophe Le Lann wrote: > Hello > > I need your opinion about my interpretation of the following GHDL > simulation. > > The design is a single-port ram with SYNCHRONOUS read. > > The testbench simply write 5 data (85..89) at (0..4), and then read the > data in the same order. > > The gtkwave waveforms are perfectly ok w.r.t my expectations. > > My problem is about the text in the terminal : > > test_mem.vhd:70:5:@390ns:(report note): 20-reading memory > test_mem.vhd:73:7:@390ns:(report note): 20-address 0 > test_mem.vhd:78:7:@410ns:(report note): 21-READ data dout 89 > test_mem.vhd:73:7:@410ns:(report note): 21-address 1 > test_mem.vhd:78:7:@430ns:(report note): 22-READ data dout 85 > test_mem.vhd:73:7:@430ns:(report note): 22-address 2 > test_mem.vhd:78:7:@450ns:(report note): 23-READ data dout 86 > test_mem.vhd:73:7:@450ns:(report note): 23-address 3 > test_mem.vhd:78:7:@470ns:(report note): 24-READ data dout 87 > test_mem.vhd:73:7:@470ns:(report note): 24-address 4 > test_mem.vhd:78:7:@490ns:(report note): 25-READ data dout 88 > > We see that at cycle 20 address=0 is generated. ok. > One cycle later (21), I expected to get the data 85 (as in the > waveform), but here the message says 89. > > Where am I wrong ?
You set the address at cycle 20 the address is latched by the synchronous memory at cycle 21 the output data is available on "dout" at "cycle 21 + t(access_time)" so you read it only at cycle 22 -- Sylvere Teissier INVIA Europarc Sainte Victoire - Bat 6 Le Canet - BP46 13590 Meyreuil Tel: 04.42.24.50.77 ------------------------------- This mail message and attachments (the "message") are solely intended for the addressees. It is confidential in nature . If you receive this message in error, please delete it and immediately notify the sender by e-mail. Any use other than its intended purpose, dissemination or disclosure, either whole or partial, is prohibited except if formal approval is granted. As communication on the Internet is not secure, the sender does not accept responsibility for the content of this message.
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