敬爱的TI工程师们，早上好！
AM3352 mmc2无法识别SD卡的问题，请求协助。谢谢！
主板概况：
我们自己定制的PCB，使用AM3352，mm0，mmc2连接SD卡设备， mmc1连接emmc设备。 mm0, mmc1及mmc2(在DTS文件中分别为mmc1, mmc2和mmc3)。其中mmc0、mm2为4-bit, mm1为8-bit。
软件平台：u-boot version: 2014.04, Linux version: bb-black-kernel-3.8.tar.bz2
问题描述：
- mmc0, mmc1可以正常工作。但是MMC2识别不到接口上SD卡信息。
问题资料：
- dts描述：
mmc3_pins: pinmux_mmc3_pins {
pinctrl-single,pins = <
0x54 0x17 /*GPMC_A5.mmc2.cs*/
0x58 0x17 /*GPMC_A6.mmc2.wake*/
0x78 0x33 /*0x23 GPMC_BEN1.d3 (MODE(3) | RXACTIVE | PULLUP_EN) */
0x4c 0x33 /* GPMC_A3.d2 (MODE(3) | RXACTIVE | PULLUP_EN) */
0x48 0x33 /* GPMC_A2.d1 (MODE(3) | RXACTIVE | PULLUP_EN) */
0x44 0x33 /* GPMC_A1.mmc2.d0 (MODE(3) | RXACTIVE | PULLUP_EN) */
0x8c 0x33 /* gpmc_clk.mmc2.clk, (MODE(3) | RXACTIVE | PULLUP_EN) */
0x88 0x33 /* gpmc_csn3.mmc2.cmd, (MODE(3) | RXACTIVE | PULLUP_EN) */
>;
};
&mmc3 {
status = "okay";
pinctrl-names = "default";
pinctrl-0 = <&mmc3_pins>;
vmmc-supply = <&&vmmcsd_fixed>;
bus-width = <0x4>;
dmas = <&edma 12
&edma 13>;
dma-names = "tx", "rx";
cd-gpios = <&gpio3 16 0>;
cd-inverted;
};
- 内核dmesg
[ 1.635057] @kernel -----> mmc_rescan_try_freq
[ 1.651504] kernel -----> Set clock to 400000Hz
[ 1.661037] @sdio-wifi -----> identify error !
[ 1.678987] @SD-TF -----> identify successful !
[ 1.683831] kernel -----> Set clock to 400000Hz
只能identify SD 卡，
都没办法找到 new high speed SDHC card at address xxxx
附：参考 processors.wiki.ti.com/.../SD-MMC_Usage_Notes_on_OMAP35x_and_AM37x 中提到：
Using MMC3
It is recommended that MMC3 be only used for 1.8V connectivity devices. It does not have an internal transceiver like MMC1 and does not have external direction signals like MMC2. It is possible to put auto direction sensing transceivers as described with MMC1, however, the buffer strength and loading constraints are restricted with MMC3. Typical buffer strengths for MMC3 is 4mA vs. 8mA for MMC1. Also, MMC1 can handle up to a 30pF load, whereas MMC3 can only handle up to 14pF load.
MMC3是否只能工作于1.8V下？
我们定制主板参照的是BBB，印象中BBB板是没有使用到MMC2口的，在VDDSHVx全部是连接到3.3v,原理图如下：
查阅了EVM板，其MMC2接了个WIFI模块,在VDDSHVx的设计如下，在使用到MMC2时，将vmmc-supply 中电压设为1.8伏，想排除下是否为硬件上问题？
