AM335X开发——设备树下增加SRAM、FPGA的GPMC设备节点
最近在做嵌入式的开发，调试的是一块搭载了AM3359、AM4379以及Cyclone10三个CPU的板子。三者的通讯主要是通过GPMC总线来实现，数据存储在一块大小为256KB的SRAM中，数据交互则通过Cyclone10这块FPGA上的双口RAM来实现。其中，AM3359这块CPU上运行了linux-rt-4.4.32实时内核。在这里，记录了GPMC调试的一些问题以及基础知识，方便后续的查阅。
一、GPMC简介
GPMC：General-purpose Memory Controller （通用存储器控制器）
特点：
1.灵活的 8 位和 16 位异步存储器接口
2.具有多达7个片选
3.支持NAND、NOR、复用NOR和SRAM
4.最大支持512MB的片外存储器连续地址空间的访问
二、GPMC与存储器的连接
1.与16位的地址数据复用存储器连接：
2.与16位的非复用存储器连接：
3.与8位的NAND FLASH连接：
三、7个配置寄存器的定义
1、配置设备类型 GPMC_CONFIG1
2、配置访问时序，主要读写时序 GPMC_CONFIG2~6
3、配置基地址、容量（即掩码地址）、使能CS信号 GPMC_CONFIG7
四、片选地址区域的划分
片选地址区域的划分主要由GPMC_CONFIG7_i[11-8]来确定当前片选地址空间的大小，GPMC_CONFIG7_i [6]控制片选引脚， GPMC_CONFIG7_i [5-0]确定当前片选的起始地址。
疑问：上图中的地址空间配置是怎样的，cpu如何选中设备？
Mask address 最小16M ，地址空间的跨度为0 ~ 0x00FF FFFF（低24位）。
Base address 由地址线的高8位决定，这个地址与当前的片选相关联。
例子：
GPMC_CONFIG7_0： 基地址规划为0x08，大小划归为16MB（0x00FF FFFF）
起始地址：0x0800 0000
结束地址： 0x08FF FFFF
GPMC_CONFIG7_2： 基地址规划为0x0A，大小规划为128MB（0x07FF FFFF）
起始地址：0x0A00 0000，
结束地址为0x0A00 0000 + 0x07FF FFFF=0x11FF FFFF
CPU访问设置好的地址范围，对应的片选引脚就会被拉低，从而选中设备
五、设备树的配置
linux内核有关gpmc的讲解可参考内核目录的下列文件：
(1)linux-rt-4.4.32/Documentation/devicetree/bindings/memory-controllers/omap-gpmc.txt
(2)linux-rt-4.4.32/Documentation/devicetree/bindings/mtd/gpmc-nor.txt
(3)linux-rt-4.4.32/Documentation/devicetree/bindings/mtd/gpmc-nand.txt
这些官方说明文档会针对设备节点的参数做一个比较详细的解释。
下面列举一下已经调试好的设备树代码：
1.NAND flash设备树的配置
调试的板子上使用的是一个8位的nandflash，型号为S34ML04G2，512MB。
①引脚配置
nandflash_pins_s0: nandflash_pins_s0 {
pinctrl-single,pins = <
AM33XX_IOPAD(0x800, (PIN_INPUT_PULLUP | MUX_MODE0)) /*gpmc_ad0.gpmc_ad0 */
AM33XX_IOPAD(0x804, (PIN_INPUT_PULLUP | MUX_MODE0)) /*gpmc_ad1.gpmc_ad1 */
AM33XX_IOPAD(0x808, (PIN_INPUT_PULLUP | MUX_MODE0)) /*gpmc_ad2.gpmc_ad2 */
AM33XX_IOPAD(0x80c, (PIN_INPUT_PULLUP | MUX_MODE0)) /*gpmc_ad3.gpmc_ad3 */
AM33XX_IOPAD(0x810, (PIN_INPUT_PULLUP | MUX_MODE0)) /*gpmc_ad4.gpmc_ad4 */
AM33XX_IOPAD(0x814, (PIN_INPUT_PULLUP | MUX_MODE0)) /*gpmc_ad5.gpmc_ad5 */
AM33XX_IOPAD(0x818, (PIN_INPUT_PULLUP | MUX_MODE0)) /*gpmc_ad6.gpmc_ad6 */
AM33XX_IOPAD(0x81c, (PIN_INPUT_PULLUP | MUX_MODE0)) /*gpmc_ad7.gpmc_ad7 */
AM33XX_IOPAD(0x870, (PIN_INPUT_PULLUP | MUX_MODE0)) /*gpmc_wait0.gpmc_wait0 */
AM33XX_IOPAD(0x87c, (PIN_OUTPUT | MUX_MODE0)) /*gpmc_csn0.gpmc_csn0 */
AM33XX_IOPAD(0x890, (PIN_OUTPUT | MUX_MODE0)) /*gpmc_advn_ale.gpmc_advn_ale */
AM33XX_IOPAD(0x894, (PIN_OUTPUT | MUX_MODE0)) /*gpmc_oen_ren.gpmc_oen_ren */
AM33XX_IOPAD(0x898, (PIN_OUTPUT | MUX_MODE0)) /*gpmc_wen.gpmc_wen */
AM33XX_IOPAD(0x89c, (PIN_OUTPUT | MUX_MODE0)) /*gpmc_be0n_cle.gpmc_be0n_cle */
>;
};②增加GPMC结点
&gpmc {
/* When enabling GPMC, disable eMMC */
status = "okay";
pinctrl-names = "default";
pinctrl-0 = <&nandflash_pins_s0>;
ranges = <0 0 0x08000000 0x1000000>; /* CS0: 16MB for NAND */
...
}
③在GPMC节点下添加NAND节点
（1）配置NAND的片选引脚、Base address 和Mask address。
（2）配置NAND的各项参数。
（3）分区。
&gpmc {
/* When enabling GPMC, disable eMMC */
status = "okay";
pinctrl-names = "default";
pinctrl-0 = <&nandflash_pins_s0>;
ranges = <0 0 0x08000000 0x1000000>; /* CS0: 16MB for NAND */
nand@0,0 {
compatible = "ti,omap2-nand";
reg = <0 0 4>; /* CS0, offset 0, IO size 4 */
interrupt-parent = <&gpmc>;
interrupts = <0 IRQ_TYPE_NONE>, /* fifoevent */
<1 IRQ_TYPE_NONE>; /* termcount */
rb-gpios = <&gpmc 0 GPIO_ACTIVE_HIGH>; /* gpmc_wait0 */
ti,nand-ecc-opt = "bch8";
ti,elm-id = <&elm>;
nand-bus-width = <8>;
gpmc,device-width = <1>;
gpmc,sync-clk-ps = <0>;
gpmc,cs-on-ns = <0>;
gpmc,cs-rd-off-ns = <44>;
gpmc,cs-wr-off-ns = <44>;
gpmc,adv-on-ns = <6>;
gpmc,adv-rd-off-ns = <34>;
gpmc,adv-wr-off-ns = <44>;
gpmc,we-on-ns = <0>;
gpmc,we-off-ns = <40>;
gpmc,oe-on-ns = <0>;
gpmc,oe-off-ns = <54>;
gpmc,access-ns = <64>;
gpmc,rd-cycle-ns = <82>;
gpmc,wr-cycle-ns = <82>;
gpmc,bus-turnaround-ns = <0>;
gpmc,cycle2cycle-delay-ns = <0>;
gpmc,clk-activation-ns = <0>;
gpmc,wr-access-ns = <40>;
gpmc,wr-data-mux-bus-ns = <0>;
/* MTD partition table */
/* All SPL-* partitions are sized to minimal length
* which can be independently programmable. For
* NAND flash this is equal to size of erase-block */
#address-cells = <1>;
#size-cells = <1>;
partition@0 {
label = "NAND.SPL";
reg = <0x00000000 0x000020000>;
};
partition@1 {
label = "NAND.SPL.backup1";
reg = <0x00020000 0x00020000>;
};
partition@2 {
label = "NAND.SPL.backup2";
reg = <0x00040000 0x00020000>;
};
partition@3 {
label = "NAND.SPL.backup3";
reg = <0x00060000 0x00020000>;
};
partition@4 {
label = "NAND.u-boot-spl-os";
reg = <0x00080000 0x00040000>;
};
partition@5 {
label = "NAND.u-boot";
reg = <0x000C0000 0x00100000>;
};
partition@6 {
label = "NAND.u-boot-env";
reg = <0x001C0000 0x00020000>;
};
partition@7 {
label = "NAND.u-boot-env.backup1";
reg = <0x001E0000 0x00020000>;
};
partition@8 {
label = "NAND.kernel";
reg = <0x00200000 0x00800000>;
};
partition@9 {
label = "NAND.file-system";
reg = <0x00A00000 0x1F600000>;
};
};
};2.NOR flash/SRAM设备树的配置
调试的板子上使用的SRAM是IS61LV25616AL这个型号，有18根地址线，16根数据线。连接的方式为AD复用模式（Address/Data-Multiplexed）。SRAM的访问方式和NOR是一致的，所以配置方法也是一样。
①引脚配置
sram_x16_default: sram_x16_default {
pinctrl-single,pins = <
AM33XX_IOPAD(0x800, (PIN_INPUT_PULLUP | MUX_MODE0)) /* gpmc_ad0.gpmc_ad0*/
AM33XX_IOPAD(0x804, (PIN_INPUT_PULLUP | MUX_MODE0)) /* gpmc_ad1.gpmc_ad1*/
AM33XX_IOPAD(0x808, (PIN_INPUT_PULLUP | MUX_MODE0)) /* gpmc_ad2.gpmc_ad2*/
AM33XX_IOPAD(0x80c, (PIN_INPUT_PULLUP | MUX_MODE0)) /* gpmc_ad3.gpmc_ad3*/
AM33XX_IOPAD(0x810, (PIN_INPUT_PULLUP | MUX_MODE0)) /* gpmc_ad4.gpmc_ad4*/
AM33XX_IOPAD(0x814, (PIN_INPUT_PULLUP | MUX_MODE0)) /* gpmc_ad5.gpmc_ad5*/
AM33XX_IOPAD(0x818, (PIN_INPUT_PULLUP | MUX_MODE0)) /* gpmc_ad6.gpmc_ad6*/
AM33XX_IOPAD(0x81c, (PIN_INPUT_PULLUP | MUX_MODE0)) /* gpmc_ad7.gpmc_ad7*/
AM33XX_IOPAD(0x820, (PIN_INPUT_PULLUP | MUX_MODE0)) /* gpmc_ad8.gpmc_ad8*/
AM33XX_IOPAD(0x824, (PIN_INPUT_PULLUP | MUX_MODE0)) /* gpmc_ad9.gpmc_ad9*/
AM33XX_IOPAD(0x828, (PIN_INPUT_PULLUP | MUX_MODE0)) /* gpmc_ad10.gpmc_ad10*/
AM33XX_IOPAD(0x82c, (PIN_INPUT_PULLUP | MUX_MODE0)) /* gpmc_ad11.gpmc_ad11*/
AM33XX_IOPAD(0x830, (PIN_INPUT_PULLUP | MUX_MODE0)) /* gpmc_ad12.gpmc_ad12*/
AM33XX_IOPAD(0x834, (PIN_INPUT_PULLUP | MUX_MODE0)) /* gpmc_ad13.gpmc_ad13*/
AM33XX_IOPAD(0x838, (PIN_INPUT_PULLUP | MUX_MODE0)) /* gpmc_ad14.gpmc_ad14*/
AM33XX_IOPAD(0x83c, (PIN_INPUT_PULLUP | MUX_MODE0)) /* gpmc_ad15.gpmc_ad15*/
AM33XX_IOPAD(0x8e0, (PIN_INPUT_PULLUP | MUX_MODE2)) /*gpmc_a1.gpmc_a1(a16)*/
AM33XX_IOPAD(0x8e4, (PIN_INPUT_PULLUP | MUX_MODE2)) /*gpmc_a2.gpmc_a2(a17)*/
AM33XX_IOPAD(0x8b8, (PIN_INPUT_PULLUP | MUX_MODE1)) /*gpmc_a6.gpmc_a6(a21)*/
AM33XX_IOPAD(0x8bc, (PIN_INPUT_PULLUP | MUX_MODE1)) /*gpmc_a7.gpmc_a7(a22)*/
AM33XX_IOPAD(0x870, (PIN_INPUT_PULLUP | MUX_MODE0)) /*gpmc_wait0.gpmc_wait0*/
AM33XX_IOPAD(0x87c, (PIN_OUTPUT | MUX_MODE0)) /* gpmc_csn0.gpmc_csn0 */
AM33XX_IOPAD(0x880, (PIN_OUTPUT | MUX_MODE0)) /* gpmc_csn1.gpmc_csn1 */
AM33XX_IOPAD(0x884, (PIN_OUTPUT | MUX_MODE0)) /* gpmc_csn2.gpmc_csn2 */
AM33XX_IOPAD(0x890, (PIN_OUTPUT | MUX_MODE0)) /*gpmc_advn_ale.gpmc_advn_ale*/
AM33XX_IOPAD(0x894, (PIN_OUTPUT | MUX_MODE0)) /*gpmc_oen_ren.gpmc_oen_ren*/
AM33XX_IOPAD(0x898, (PIN_OUTPUT | MUX_MODE0)) /* gpmc_wen.gpmc_wen */
AM33XX_IOPAD(0x89c, (PIN_OUTPUT | MUX_MODE0)) /*gpmc_be0n_cle.gpmc_be0n_cle*/
>;
};②增加GPMC节点
&gpmc {
/* When enabling GPMC, disable eMMC */
status = "okay";
pinctrl-names = "default";
pinctrl-0 = ;
ranges = <0 0 0x08000000 0x01000000>, /* CS0 nand. Min partition = 16MB */
<1 0 0x01000000 0x01000000>, /* CS1 sram. Min partition = 16MB */
<2 0 0x02000000 0x01000000>; /* CS2 fpga. Min partition = 16MB */
...
}③在GPMC节点下添加NOR节点
（1）配置NOR的片选引脚、Base address 和Mask address。
（2）配置NOR的各项参数。
（3）分区。(不是必须的)
nor1@1,0 {
compatible = "cfi-flash";
linux,mtd-name= "intel,pf48f6000m0y1be";
#address-cells = <1>;
#size-cells = <1>;
reg = <1 0 0x01000000>;
bank-width = <2>;
gpmc,mux-add-data = <2>;
gpmc,cs-on-ns = <0>;
gpmc,cs-rd-off-ns = <279>;
gpmc,cs-wr-off-ns = <279>;
gpmc,adv-on-ns = <18>;
gpmc,adv-rd-off-ns = <72>;
gpmc,adv-wr-off-ns = <72>;
gpmc,oe-on-ns = <81>;
gpmc,oe-off-ns = <252>;
gpmc,we-on-ns = <81>;
gpmc,we-off-ns = <252>;
gpmc,rd-cycle-ns = <279>;
gpmc,wr-cycle-ns = <279>;
gpmc,access-ns = <171>;
gpmc,wr-data-mux-bus-ns = <135>;
gpmc,wr-access-ns = <279>;
};
nor2@2,0 {
compatible = "cfi-flash";
linux,mtd-name= "intel,pf48f6000m0y1be";
reg = <2 0 0x01000000>;
#address-cells = <1>;
#size-cells = <1>;
bank-width = <2>;
gpmc,mux-add-data = <2>;
gpmc,cs-on-ns = <0>;
gpmc,cs-rd-off-ns = <186>;
gpmc,cs-wr-off-ns = <186>;
gpmc,adv-on-ns = <12>;
gpmc,adv-rd-off-ns = <48>;
gpmc,adv-wr-off-ns = <48>;
gpmc,oe-on-ns = <54>;
gpmc,oe-off-ns = <168>;
gpmc,we-on-ns = <54>;
gpmc,we-off-ns = <168>;
gpmc,rd-cycle-ns = <186>;
gpmc,wr-cycle-ns = <186>;
gpmc,access-ns = <114>;
gpmc,wr-data-mux-bus-ns = <90>;
gpmc,wr-access-ns = <186>;
};上面这里是设置了两个节点，一个是sram，一个是fpga，分别对应片选1和片选2。
六、注意事项
1.片选0在系统上电或者复位之后，自动会变为使能状态（低电平）。
Chip-select 0 is the only chip-select region enabled after either a power-up or a GPMC reset.
2.在设置sram或者nor的时候，需注意：
To select an address/data-multiplexed device, program the following register fields:
• GPMC_CONFIG1_i[11-10] DEVICETYPE field = 00
• GPMC_CONFIG1_i[9-8] MUXADDDATA bit = 10b
3. 掩码地址应该避免0010 和1001这两个值。
A mask value of 0010 or 1001 must be avoided because it will create holes in the chip-select address space.
4.查看AM335X的数据手册，会发现GPMC在与外部的16位地址数据复用存储器连接时，地址线错开了一位来连接：
这是由于AM335X的内部储存结构是以字节为单位的，但外部储存器的结构是以字为单位的。
CPU地址 16位存储器的地址
0x00,0x01 0x00（0x1234）（此地址对应一个16bit的数据）
0x02,0x03 0x01（0x5678）
0x04,0x05 0x02（0xabcd）
CPU地址线 16位存储器的地址
A0 x
A1 A0
A2 A1
A3 A2
… …