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

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

On 2017-Jun-24, at 3:21 PM, John Klos <john at ziaspace.com> wrote:

>> SD High-Speed mode is speed/performance-wise equivalent to UHS SDR25 mode, which runs the bus up to 50MHz and can do up to 25MB/s transfers. The difference between High-Speed and SDR25 is signalling voltage (3.3V vs 1.8V).
>> 
>> UHS SDR50 mode runs the bus up to 100MHz and can do up to 50MB/s transfers. 1.8V signaling is the only option here.
> 
> We know that SDR50 mode works with many, perhaps most, cards under NetBSD. We can get greater than 25 MB/sec actual transfer on some cards. That means that SDR50 (100 MHz clock, 50 MB/sec) is supported in hardware and works:

Good to know.

> frigg# dd if=/dev/rld0b of=/dev/null bs=4m
> 256+0 records in
> 256+0 records out
> 1073741824 bytes transferred in 40.947 secs (26222722 bytes/sec)

Not the best of examples:

25 * 1024*1024 = 26214400

26222722
vs.
26214400

could well be in the noise for the time accuracy
or how exact the clock rate is vs. nominal.

(I'm not saying that you are wrong, just that the
example is not clearly faster than a nominal 25 MB/s.)

> Some cards don't work at SDR50 speeds. We can:
> 
> 1) Have a boot-time option in cmdline.txt or config.txt which selects a slower mode
> 
> 2) Have the kernel try slower modes if we get "cmd end bit error" events
> 
> 3) Have all Pis with all fast cards run slower :P


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