serial Flash over SPI as rootdevice?

serial Flash over SPI as rootdevice?

[Alexander Stein]

Hello,

is it currently possible to use a serial Flash connected over SPI to use as a rootdevice?
If not, would it be possible and which drivers need to be written for that then?

Best regards,
Alexander

Re: serial Flash over SPI as rootdevice?

[Thomas.Betker]

Hello Alexander:

> is it currently possible to use a serial Flash connected over SPI to
> use as a rootdevice?
> If not, would it be possible and which drivers need to be written 
> for that then?

Yes, it is certainly possible; we are doing it ourselves. No extra drivers 
are required for this beyond those you need anyway (SPI driver, SPI flash 
driver).

The real problem, though, is that you cannot boot from standard SPI flash. 
For this, you need memory which can be read directly by the CPU, such as 
parallel NOR flash.

Best regards,
Thomas

Re: serial Flash over SPI as rootdevice?

[Alexander Stein]

Hello Thomas,

On Tuesday 09 April 2013 10:21:26, Thomas.Betker@rohde-schwarz.com wrote:
> Hello Alexander:
> 
> > is it currently possible to use a serial Flash connected over SPI to
> > use as a rootdevice?
> > If not, would it be possible and which drivers need to be written 
> > for that then?
> 
> Yes, it is certainly possible; we are doing it ourselves. No extra drivers 
> are required for this beyond those you need anyway (SPI driver, SPI flash 
> driver).

That sound great. Could you please point me to the driver needed for that? Do you have any performance comparisons to e.g. NOR flash?

> The real problem, though, is that you cannot boot from standard SPI flash. 
> For this, you need memory which can be read directly by the CPU, such as 
> parallel NOR flash.

Well, the idea is to use an AT91 which can boot directly from serial flash with it's own ROM code. This would load the bootloader (will be u-boot likely) which in turns needs to fetch the kernel from the serial flash too. Should be possible, no?

Best regards,
Alexander