Character LCD on DSP Development Kit, Stratix III Edition

You can use some signaltap probes to see what is sent to the LCD controller and check if it is ok.

How high is your clk frequency? If it is coming directly from the oscillator it is probably too high. You should use a counter in your process and only update your signals (including lcd_enable) only every n clock cycles.

And while I'm at it, try to use ieee.numeric_std with the "unsigned" and "signed" types instead of ieee.std_logic_unsigned. It is standard and will cause less confusion when mixing unsigned and signed vectors.