Re: 2017-06-20-netbsd-raspi-earmv6hf.img

[Mark Millard <markmi%dsl-only.net@localhost>]

[I see that I made an mis-edit for SDR25's
name in one place, listing SDR50 instead.
So a correction. . .]

On 2017-Jun-24, at 2:05 PM, Mark Millard <markmi at dsl-only.net> wrote:

> On 2017-Jun-24, at 1:05 PM, Michael van Elst <mlelstv at serpens.de> wrote:
> 
>> jmcneill at invisible.ca (Jared McNeill) writes:
>> 
>>> Not sure the point of this link, the thread is full of confusion.
>> 
>>> One of the posters says: "The Pi uses SD High-speed mode (SDR50) at 
>>> 25MB/s", but this is not true at all.
>> 
>> Should probably read "SD High-speed mode (50MHz) at 25MB/s". And
>> that's true again.
> 
> I was confused so I tried to look up terminology
> and came up with: 
> 
> https://www.sdcard.org/press/past_evens/pdf/SD_Standards_and_Technology_GWTaipei_Oct2014.pdf
> 
> and its page labeled 7.
> 
> It shows the following as distinct:
> 
> (Bus Speed                 Signal  Bus Max
> mode)           Max Freq.  Voltage performance   Spec. version
> --------------  -------    ----    -------       ----
> High Speed (HS)  50 MHz    3.3V    25 MB/s       1.1
> 
> UHS-I SDR50     100 MHz    1.8V    50 MB/s       3.01
> 
> HS is closer in characteristics to UHS-I SDR25:
> 
> UHS-I SDR50      50 MHz    1.8V    25 MB/s       3.01

Correction to the above line (to "SDR25"):

UHS-I SDR25      50 MHz    1.8V    25 MB/s       3.01

> (so 3.3V vs. 1.8V).
> 
> As for UHS-I DDR50:
> 
> UHS-I DDR50      50 MHz    1.8V    50 MB/s       3.01
> 
> So both 1.8V --and 50MB/s despite the same Max Freq.
> (via using both edge directions).
> 
> 
> My guess is that something named: SDHC_SDR50_SUPP is
> more like for enabling:
> 
> UHS-I SDR50     100 MHz    1.8V    50 MB/s       3.01
> 
> which between Max Frequency and Voltage would tend to
> have support in fewer places than High Speed (HS) would.
> 
> Matching Max Frequency also gets the same Bus Max
> performance:
> 
> UHS-I SDR25      50 MHz    1.8V    25 MB/s       3.01


===
Mark Millard
markmi at dsl-only.net