PWM chip is [http://www.fpga4fun.com/PWM_DAC.html PWM_DAC fpga4fun] one. Warning, using PWM as it can result into a low quality sound, in fact if sound is stopped at 50% of voltage, it generates continious high-sound or ultrasound during this "silent" moment (cause it can't really make 2.5v with only two output 0v and 5v), so you can hear whistle. A solution is to '''add another clock entry''', one clock is about executing PWM algorithm and another one is about pushing input digital sound data, that result a higher quality sound, that what I done in MiST-board version of FPGAmstrad.
In NEXYS2's version of FPAmstrad, PS/2 keyboard had a strange internal hardware timeout, it can be shown using game "Macadam" (pinball), I solved this problem since NEXYS4's version of FPGAmstrad (and then also in MiST version)
VGA display component use same parameters than unix '''modeline''' command