Hi all,

The custom AT91SAM9G20 board I've been working on is now close to working. I can load the Linux kernel via TFTP, but I'd like to pull it from a serial flash on CS0.

I can load U-boot from my serial flash with AT91Bootstrap, so I know the hardware works. I've customized U-boot v2010.09 with the changes you can see here: https://github.com/rascalmicro/u-boot-r ... 148d843a8a The spi.c I'm using is a duplicate of the same file found in board/calao/sbc35_a9g20/.

This seems like it should work. However, when I issue the sf probe command, I see this:
U-Boot> sf probe 0
SF: Unsupported manufacturer 00
Failed to initialize SPI flash at 0:0

My impression from the conclusion of this monster thread: http://www.at91.com/forum/viewtopic.php ... sk,t/sd,a/ is that what I'm trying to do is possible.

Any suggestions? Do I need to specify certain speeds or modes to make it work?

Is there any code to initialize the GPIO pins? The Linux code treats the -CS pins as bit-banged GPIO pins, whereas ATMEL's code tends to set them in the SPI controller for it to control automatically. They might not be set in the way you need them.

It took a little bit of digging, but I figured this one out. CptTitanic, you were on the right track-- thanks.

As Titanic noted, the CS line can be controlled by the SPI hardware or by U-boot as GPIO. If the SPI hardware is allowed to control the CS line, when the "read id" command is issued, the CS line goes high briefly between the command and the 5 bytes of clock signal sent to crank out the ID in response. Unfortunately, this violates the spec of the Macronix serial flash, and even worse, it doesn't work. The CS line has to stay low for the duration of the command and response.

Switching to U-boot control of the CS line fixes the problem. I did this with the following line added to atmel_spi.c just before the return of spi_setup_slave():

at91_spi0_hw_init(1 << 4);

Thanks again for the hint, Titanic.

That belongs into your board specific file. Do not modify common sources!
About like that:

int board_init(void)
{
...
#ifdef CONFIG_ATMEL_SPI0
/* (n+4) denotes to use nSPISEL(0) in GPIO mode! */
at91_spi0_hw_init(1 << (FRAM_CS_NUM + 4));
#endif
#ifdef CONFIG_ATMEL_SPI1
at91_spi1_hw_init(1 << (ENC_CS_NUM + 4));
#endif
...
return 0;
}