From 7a6e56492cd5d446007d6bfe851d14ee3a850aa7 Mon Sep 17 00:00:00 2001 From: Werner Almesberger Date: Fri, 12 Apr 2013 17:38:31 -0300 Subject: [PATCH] edid.py: sample SCL only every 64 clock cycles, to avoid bouncing Possibly due to SCL rising fairly slowly (in the 0.5-1 us range), bouncing has been observed while crossing the "forbidden" region between Vil(max) and Vih(min). By lowering the sample rate from once per system clock to once every 64 clock cycles, we make sure we sample at most once during the bounce interval and thus never see a false edge. (Although we may see a rising edge one sample time late, which is perfectly harmless.) --- milkymist/dvisampler/edid.py | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-) diff --git a/milkymist/dvisampler/edid.py b/milkymist/dvisampler/edid.py index 4c9da4209..f42b9dfdf 100644 --- a/milkymist/dvisampler/edid.py +++ b/milkymist/dvisampler/edid.py @@ -23,24 +23,25 @@ class EDID(Module, AutoCSR): ### - scl_i = Signal() + scl_raw = Signal() sda_i = Signal() sda_drv = Signal() _sda_drv_reg = Signal() _sda_i_async = Signal() self.sync += _sda_drv_reg.eq(sda_drv) self.specials += [ - MultiReg(pads.scl, scl_i), + MultiReg(pads.scl, scl_raw), Tristate(pads.sda, 0, _sda_drv_reg, _sda_i_async), MultiReg(_sda_i_async, sda_i) ] - # FIXME: understand what is really going on here and get rid of that workaround - for x in range(20): - new_scl = Signal() - self.sync += new_scl.eq(scl_i) - scl_i = new_scl - # + scl_i = Signal() + samp_count = Signal(6) + samp_carry = Signal() + self.sync += [ + Cat(samp_count, samp_carry).eq(samp_count + 1), + If(samp_carry, scl_i.eq(scl_raw)) + ] scl_r = Signal() sda_r = Signal()