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

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

On 2017-Jun-24, at 1:05 PM, Michael van Elst <mlelstv%serpens.de@localhost> wrote:

> jmcneill%invisible.ca@localhost (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

(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