Openwrt adds support for SD card

One 、 Hardware platform

1.1  controller ：MT7620（A9 kernel ）

Two 、 software platform

2.1、 development environment ：Ubuntu12.04 
2.2、 Software version ：openwrt  official 15.05 edition SDK Development kit （CHAOS CALMER 15.05 edition ）

3、 ... and 、 Functional specifications

 The target chip selected in this article is MT7620,profile  The choice is “Xiaomi MiWiFi Mini ”.
 about openwrt Increase for sd card Support for , Four aspects need to be configured ：
1、dts File add pair sdhci Support for , Turn on the hardware pair sd card Interface driver support , Hardware initialization .
2、 Add to sd card Driver support for , Used to detect sd card Plug and drive .
3、 Add support for language formats , Such as utf8、cp437、iso8859-1, Used to identify sd card What's in it , Avoid random code .
4、 Add to vfat File system support , Otherwise, you cannot mount sd card.

Four 、 Operation steps

4.1 modify dts file

For the default Xiaomi development board dts file , No, right sd Hardware initialization of the interface , Therefore, it needs to be modified “openwrt/target/linux/ramips/dts/XIAOMI-MIWIFI-MINI.dts” file .
In the document , Add the following code ：

        sdhci@10130000 {
                compatible = "ralink,mt7620-sdhci";
                reg = <0x10130000 4000>;

                interrupt-parent = <&intc>;
                interrupts = <14>;

                status = "okay";
        };

4.2 increase sd card Drive support

stay openwrt sdk In bag , Carry out orders make menuconfig command .
Kernel modules —> Other modules —>
-*- kmod-sdhci…………..
<*> kmod-sdhci-mt7620
Configuration is shown in figure 4-1 Shown .

chart 4-1 increase sd card Interface drive

matters needing attention ： stay make menuconfig Configuration of the sd card drive , No more make kernel_menuconfig Middle configuration sd card drive , Otherwise, when starting up , A message appears ：

mmc_core: exports duplicate symbol __mmc_claim_host (owned by kernel)
sdhci-pltfm: SDHCI platform and OF driver helper
mmc_core: exports duplicate symbol __mmc_claim_host (owned by kernel)
mmc_core: exports duplicate symbol __mmc_claim_host (owned by kernel)
mmc_core: exports duplicate symbol __mmc_claim_host (owned by kernel)
mmc_core: exports duplicate symbol __mmc_claim_host (owned by kernel)
mmc_core: exports duplicate symbol __mmc_claim_host (owned by kernel)

As shown in the prompt ,sd card mmc_core Duplicate export , So eventually, it can't sd Card drive succeeded ！！！！

4.3 Add language module support

about openwrt System , Just turn on sd card Interface driver is not enough , You also need to add language support , otherwise sd card Unable to recognize the contents of the file , Or garbled code appears .
stay openwrt sdk In bag , Carry out orders make menuconfig command .
Kernel modules —> Native Language Support —>,
<*> kmod-nls-cp437
<*> kmod-nls-iso8859-1
<*> kmod-nls-utf8
The setting is as shown in the figure 4-2 Shown .

chart 4-2 Add language support

For language , The explanation is as follows ：
nls codepage 437 – The United States / Canadian English
nls codepage 737 – Greek
nls codepage 775 – Baltic
nls codepage 850 – Including Western European languages ( German , Spanish , Italian ) Some characters in
nls codepage 852 – Latin 2 Including central and Eastern European languages ( albanian , Croatian , Czech , English , Finnish language , Hungarian , irish , German , Polish language , Romanian , Serbian , Slovak , Slovenian ,Sorbian language )
nls codepage 855 – Slavic
nls codepage 857 – Turkish language
nls codepage 860 – Portuguese
nls codepage 861 – Icelandic
nls codepage 862 – Hebrew
nls codepage 863 – Canadian
nls codepage 864 – The Arabic language
nls codepage 865 – Germanic
nls codepage 866 – Slavic / Russian
nls codepage 869 – Greek (2)
nls codepage 874 – Thai,
nls codepage 936 – Simplified Chinese GBK
nls codepage 950 – Traditional Chinese Big5
nls iso8859-1 – Western European languages ( albanian , Spanish Catalan , Danish language , Dutch , English ,Faeroese language , Finnish language , French , German , Galician , irish , Icelandic , Italian , Norwegian , Portuguese , Swiss .) This also applies to American English .
nls iso8859-2 – Latin 2 Character set , Slav / Central European languages ( Czech , German , Hungarian , Polish language , romanian , Croatian , Slovak , Slovenian )
nls iso8859-3 – Latin 3 Character set , ( Esperanto , Galician , Maltese , Turkish language )
nls iso8859-4 – Latin 4 Character set , ( Ethanian , Latvian , Lithuanian ), yes Latin 6 The pre order standard of character set
nls iso8859-5 – Slavic ( Bulgarian ,Byelorussian language , Macedonian , Russian , Serbian , Ukrainian ) Generally recommended KOI8-R codepage
nls iso8859-6 – The Arabic language .
nls iso8859-7 – Modern Greek
nls iso8859-8 – Hebrew
nls iso8859-9 – Latin 5 Character set , ( Removed Latin 1 Some Icelandic characters that are not often used in Chinese are replaced by Turkish characters )
nls iso8859-10 – Latin 6 Character set , ( Inuit ( Greenland ) language , Samoan, etc Latin 4 Nordic languages not included in )
nls iso8859-15 – Latin 9 Character set , yes Latin 1 Updated version of the character set , Remove some uncommon characters , Increased support for the ethanian language , Revised French and Finnish , Added Euro characters )
nls koi8-r – Default support for Russian

4.4 increase vfat File system support

For the increase vfat File system support , There are two ways , Just choose one .

4.4.1、menuconfig Increase support

perform make menuconfig
Filesystems —>
Configuration is shown in figure 4-3 Shown .

chart 4-3 increase vfat File system support

4.4.2 kernel_menuconfig Increase support

perform make kernel_menuconfig
File systems —> DOS/FAT/NT Filesystems —>

chart 4-4 increase vfat File system support

such ,openwrt Configuration complete .

5、 ... and 、 test

After burning the program , About SD The boot information of the card is as follows ：

[ 9.050000] MTK MSDC device init.
[ 9.090000] mtk-sd: MediaTek MT6575 MSDC Driver
[ 9.090000] sdhci: Secure Digital Host Controller Interface driver
[ 9.100000] sdhci: Copyright(c) Pierre Ossman
[ 9.110000] sdhci-pltfm: SDHCI platform and OF driver helper
[ 9.140000] mmc0: new high speed SD card at address b368
[ 9.150000] mmcblk0: mmc0:b368 00000 1.86 GiB (ro)
[ 9.160000]  mmcblk0:

take sd Mount the card

root@OpenWrt:/# mount -t vfat /dev/mmcblk0 /mnt/

see sd The contents of the card , Pictured 5-1 Shown .

chart 5-1 sd Card content