Can't boot from eMMC in Standard Speed Mode at -30degC

Question

At -15degC its ok but it needs to boot at -30degC.

I have at least 2 rev C Picozed 7030's with this problem and have complied with the advisory note by operating in standard speed mode at 25MHz (section 3.7 in the Avnet Errata). Signal eMMC_CLK has been measured at 25MHz to verify this.

Do I have faulty boards, or is there anything else I've overlooked ?

I can provide screen dumps from the serial port or other information as required.

Please advise.

zedhed · Accepted Answer

Hi robertdf,

I will strongly reinforce what emphasize the recommendation that @fletch suggested above for switching to Rev. E hardware, it is the best way to correct for the cold boot issue on older PicoZed boards.

Take a look at this thread for additional details:

http://picozed.org/content/picozed-fails-load-os-emmc-low-temp

In the meantime, I hope the changes I list below will allow you to test out Standard Speed Mode with your version of U-boot and PetaLinux. The line numbers referenced below are for the 2015.4 versions of U-Boot code that we modified under the hood of PetaLinux tools to validate the change to slower speed and Standard Mode will positively affect the colder temperature boot conditions for board revisions prior to Rev. E hardware.

U-boot mmc.c file:

1) Comment out lines 1444-1446 which are:

if (mmc->card_caps & MMC_MODE_HS_52MHz)
mmc->tran_speed = 52000000;
else

2) Add the following lines after line 1451, which is:

mmc_set_clock(mmc, mmc->tran_speed);
err = mmc_switch(mmc, EXT_CSD_CMD_SET_NORMAL, EXT_CSD_HS_TIMING, 0);
if (err)
printf("Error setting STD Speed Mode
");
else
printf("-----------Set EMMC to Standard Speed Mode
");

U-boot zynq_sdhci.c file:

1) Add the following lines after lines 28-29, which are:

host->quirks = SDHCI_QUIRK_WAIT_SEND_CMD | SDHCI_QUIRK_BROKEN_R1B;
#ifdef CONFIG_ZYNQ_HISPD_BROKEN
host->quirks ^= SDHCI_QUIRK_NO_HISPD_BIT;
printf("------ SDIO Controller set to Standard Speed Mode
");
#endif

U-boot platform-top.h (or any other convenient location)

1) Define the following parameter:

#define CONFIG_ZYNQ_HISPD_BROKEN 1

For PetaLinux configuration:

1) Set device tree property 'broken-mmc-highspeed' in the sdhci node
2) Set the u201Cmax-frequencyu201D property to 25000000

This should then set the PicoZed to operate the SDIO interface to the eMMC in Standard Speed Mode, which is also called u201Cbackward-compatible card interface timing.u201D The best practice here would be for you to probe the signals going to and from the eMMC with an oscilloscope and you would see that CMD and IO transition on the falling edge of the clock. If you see this happening, then you know that the correct settings for the host SD controller are in place.

I am not sure how this would translate to the meta-xilinx Yocto recipe layers you are using to build Linux and U-Boot, but if you are using later versions of U-Boot and Linux Kernel (post 2016.2 PetaLinux release), then the patches posted here might provide some additional guidance on where to implement the appropriate changes:

https://github.com/Avnet/software/tree/master/petalinux/configs/u-boot

Specifically, these patches should be relevant:

https://github.com/Avnet/software/blob/master/petalinux/configs/u-boot/mmc.c.emmc_boot.patch
https://github.com/Avnet/software/blob/master/petalinux/configs/u-boot/platform-auto.h.emmc_boot.patch

Plus this devicetree:

https://github.com/Avnet/software/blob/master/petalinux/configs/device-tree/system-conf.dtsi.pz

Keep in mind, a slower eMMC interface does affect your boot time by increasing it. The best solution is to use Rev. E PicoZed hardware at full eMMC clock rate.

Please feel free to give this a try on your end and let us know how it goes.

Best Regards,

-Kevin