[Letux-kernel] X1600 / LX16 support - here: adding MMC - MAJOR BREAKTHROUGH

H. Nikolaus Schaller hns at goldelico.com
Sun Feb 11 17:26:34 CET 2024


Paul,

> Am 11.02.2024 um 17:19 schrieb Paul Boddie <paul at boddie.org.uk>:
> 
> On Sunday, 11 February 2024 08:50:53 CET H. Nikolaus Schaller wrote:
>> 
>> So the main factor is indeed the SD card speed (and clock calculations).
>> Reduced bus width may work with some SD cards and X1600 unit.
> 
> Yesterday, I found that switching to 1-bit bus width allowed data transfers to 
> finally work. I aim to investigate 4-bit mode today, which should be supported 
> by SD cards, but I imagine that it is more complicated than it appears.

I wasn't able to make my SD cards better work in 1-bit mode but with lower
clock rate. So I think there is no problem in 1/4 bit code to look for.

> 
> For instance, a command is needed to set the bus width on SD cards: they start 
> out in 1-bit mode and need to be told to switch to 4-bit mode.

Indeed.

> It isn't enough 
> to tell the SoC to use 4-bit mode, but I suppose the Linux framework knows 
> about this already.

What I assume is that 1-bit mode may run generally slower or some cards
may be more robust to overclocking in 1-bit mode than in 4 bit mode (where
e.g. alignment of 4 data bits to a clock line must be guaranteed).

Since I have everything working well in 4 bit mode just with slower clock we
can IMHO focus on the clock setup now.

BR,
Nikolaus



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