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[Reply #15 on:]

Sadly, the W5100 requires four byte on the SPI bus to transfer one data byte.  Here is a quote from the datasheet.

Oh, well, there's not much to be done about it.    :-(

75 kbytes/sec is the target speed then...!

I think I can get pretty close to that with a few more changes.

[Reply #16 on:]

75 kbytes/sec is the target speed then...!

With a bit more fiddling I got it up to about 50kbytes/sec ... that's about 2/3 of theoretical maximum speed.

Where's the rest? Well...50k bytes/sec is about 100 SD card sector reads. Each sector read takes a little over 3 ms so that's over 300 ms each second spent reading the SD card ... about 1/3 of the available time.

2/3 + 1/3 = 1

I guess I've hit the limit... 

[Reply #17 on:]

I think the Enet library uses the default SPI clock of F_CPU/4 or 4 MHz with a 16 MHz CPU.  The W5100 should work with a faster SPI clock.

You might be able to go faster with an 8 MHz SPI clock.  You need to set the SP2X bit in SPSR.

If you are using the SD.h library, which is a wrapper for an old version of my SdFat library, it sets SPI clock to F_CPU/4 so don't set the SP2X bit until the SD library is initialized.

My new SdFat library sets the SPI speed each time it accesses the bus so you should initialize it at 8 MHz and the Enet will also run at 8 MHz.

[Reply #18 on:]

You might be able to go faster with an 8 MHz SPI clock.  You need to set the SP2X bit in SPSR.

I just put "SPI.setClockDivider(SPI_CLOCK_DIV2);" in my setup() function and the speed went from 50kbytes/sec to 67 kbytes/sec - a pretty good gain.

What's the spec of the W5100? Is that speed within its tolerances? How about the SD card...?

[Reply #19 on:]

PS: If you want to try it out you can click here: http://87.221.151.193/index.html

That page is currently being served by the Arduino (it's a mirror of my site at www.artlum.com).

nb. The IP address is dynamic so it will probably change as soon as I post this... 

There's a big image of David Cuartielles on there, click on the little picture of him about a third of the way down the Gameduino page. See how long it takes to load ... on the local network it takes about 30 seconds.

[Reply #20 on:]

SD cards are 25 or 50 MHz depending on the card version.  

The W5100 specs rise and hold times that imply about 10 MHz max.

The Arduino is 8 MHz max.

Note that setClockDivider may not always work since libraries set the SPI speed to anything they want and do not restore it.

[Reply #21 on:]

I was just sitting here and I saw some activity on the Arduino server...

I looked at the HTTP headers on the server log and it says:

Code:

GET /robots.txt HTTP/1.1
Host: 87.221.151.193
Connection: Keep-alive
Accept: text/plain,text/html
From: googlebot(at)googlebot.com
User-Agent: Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)
Accept-Encoding: gzip,deflate

GET /index.html HTTP/1.1
Host: 87.221.151.193
Connection: Keep-alive
Accept: */*
From: googlebot(at)googlebot.com
User-Agent: Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)
Accept-Encoding: gzip,deflate

Looks like my Arduino just got visited by the Google bot!