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RFC: phy: restore operation at lower (50MHz) sys-clk-freq #33

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May 28, 2024
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RFC: phy: restore operation at lower (50MHz) sys-clk-freq #33

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4 changes: 2 additions & 2 deletions litesdcard/phy.py
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Original file line number Diff line number Diff line change
Expand Up @@ -62,14 +62,14 @@ def __init__(self):
# SDCard CE Generation.
clk_d = Signal()
self.sync += clk_d.eq(clk)
self.sync += self.ce.eq(clk & ~clk_d)
self.comb += self.ce.eq(clk & ~clk_d)

# Ensure we don't get short pulses on the SDCard Clk.
ce_delayed = Signal()
ce_latched = Signal()
self.sync += If(clk_d, ce_delayed.eq(self.clk_en))
self.comb += If(clk_d, ce_latched.eq(self.clk_en)).Else(ce_latched.eq(ce_delayed))
self.sync += self.clk.eq(~clk & ce_latched)
self.comb += self.clk.eq(~clk & ce_latched)
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@gsomlo gsomlo May 19, 2024 •
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@enjoy-digital : I've understood and agree with all the rest of the changes in commits 1a3d474 and 15bc2db, but not sure why self.ce and self.clk were switched to sync from the original comb. It is the reason sdcard breaks at lower (50MHz) system clock frequencies.

To be honest, though, I also don't get why this change breaks sdcard at low speeds :)


# SDCard PHY Read ----------------------------------------------------------------------------------

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