cards for the uSD slot (was Re: Battery and power questions)

Werner Almesberger werner at openmoko.org
Tue Nov 2 16:28:18 EDT 2010


Ron K. Jeffries wrote:
> Roughly what speed in bits per second would you estimate
> a microsd/spi interface from Ben can achieve?

Just tested it. I got 2.4 Mbps, best-case, which is a bit faster than
I thought I had seen in earlier experiments. The code in question
looks like this:


static void snd(uint16_t v)
{
	int i;

	for (i = 0; i != 16; i++) {
		if ((v >> i) & 1)
			PDDATS = X;
		else
			PDDATC = X;
		PDDATS = Y;
		PDDATC = Y;
	}
}

...

	while (1)
		snd(0x555f);


Here's a picture to prove it:

http://downloads.qi-hardware.com/people/werner/tmp/usdbb.png

There is a fair amount of background activity, which "steals" cycles,
so continuous data transmission without suppressing other system
activity may only be about half as fast.

- Werner




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