[U-Boot] [linux-sunxi] Re: [PATCH v2] sunxi: Support booting from SPI flash

[Siarhei Siamashka]

Hello,

On Wed, 8 Jun 2016 02:56:41 -0700 (PDT)
boobwrt at gmail.com wrote:

> Hello
> 
> Nice to see new entry to boot.
> I would like to know if sdcard wired in spi mode can working with
> this spi boot support.

No, it can't. The SPI protocol used by the SD card is different
from the SPI protocol used by the SPI flash chips. The SPI is just
an underlying bus to send and receive data, but the higher level
protocols are incompatible.

> Why put sdcard in spi when i have an sdcard slot? :)
> Just to solder it for bypass crappy sdcard socket pin contact

You can still solder the SD card instead of plugging it into
the SD card slot.

In fact, that's how it is usually done with eMMC. And you can even
buy some development boards with eMMC instead of experimenting
with this stuff yourself.

> then boot from usb.
> microsd was cheap in 512mb size or less.

The price difference between the Orange Pi PC and the Orange Pi PC Plus
boards is not very big:

http://www.aliexpress.com/store/product/Orange-Pi-PC-linux-and-android-mini-PC-Beyond-Raspberry-Pi-2/1553371_32448079125.html
http://www.aliexpress.com/store/product/Orange-Pi-PC-Plus-ubuntu-linux-and-android-mini-PC-Beyond-Raspberry-Pi-2/1553371_32668618847.html

For extra 4.45 EUR you get a 8GB eMMC and also some sort of WiFi.
And the eMMC is also much faster than a regular SD card, so it's
not a very bad deal.

> Is there limitation in chip memory selection?

Any SPI flash chip should be supported if it uses the right voltage
(compatible with 3.3V) and supports the Read Data Bytes command (the
opcode 0x03, followed by a 24-bit address). You can always check the
datasheet.

A suitable SPI flash chip, which seems to cost only 4 cents, is
sold here:

http://www.aliexpress.com/item/W25Q16BVSSIG-W25Q16BVSIG-2MB-SOP8/32660083443.html

But I have no idea if this particular seller is trustworthy. One can
still easily find similar chips for around 10 cents in other places.

The SPI flash is cheaper than the eMMC if we look at the absolute
price. But the price per megabyte is an entirely different story.

For U-Boot you would need a 1 MiB (8 Mbit) chip, just check the
size of the u-boot-sunxi-with-spl.bin file and ensure a bit of
extra headroom.

> Anyway thank for new support 

Thanks.

-- 
Regards,
Sierž