Shulou(Shulou.com)06/02 Report--

1. Hardware features:

(1) memory: there are two types of memory, SRAM (Static RAM) and DRAM (Dynamic RAM), which are called static memory and dynamic memory respectively.

SRAM: static memory, characterized by small capacity and high price. The advantage is that it can be powered on directly without software initialization, and the information stored internally can be read and executed.

DRAM: dynamic memory, characterized by large capacity and low price. The disadvantage is that it can not be used directly after being powered on, and it can only be used after initialization by the software.

(2) external memory: there are many types of external memory, which are simply mentioned here, NandFlash and NorFlash.

NorFlash: characterized by small capacity and high price. The advantage is that it can be directly connected to the CPU bus, and the code can be read and accessed directly after CPU is powered on, which is generally used as a startup medium.

NandFlash: it is characterized by large capacity and low price. The disadvantage is that it can not be accessed directly by bus, that is, the code can not be read directly after power-on, and it needs to be initialized by CPU, and then read and write through the sequential interface.

2. The hardware characteristics of S5PV210 chip:

The screenshot above is from sumsung S5PV210's data manual.

The S5PV210 microprocessor is based on Cortex A8. The SoC has an IROM of 64KB (NorFlash type), a SRAM of 96KB, and various types of controllers, including: SDRAM controller, 4-bit / 8-bit high-speed SD/MMC controller, NandFlash controller, OneNand controller, eSSD controller, UART/USB controller.

S5PV210 chip has built-in many types of controllers, so S5PV210 supports many ways of starting (above built-in controllers). As long as the dial switch of the OM pin is adjusted to the corresponding type, it can be started in a corresponding way. The startup methods supported by S5PV210 are shown below:

3. OM pin configuration:

4. Now, let's look at the startup process of S5PV210:

(1) after CPU is powered on, first read the preset code (BL0) from the IROM inside the S5PV210 (this code is built-in when the chip leaves the factory, because you don't know what the external equipment will be connected to in the future, so it is just a simple initialization of the chip), and then execute. What does this code BL0 do? As shown below:

BL0 first turns off the watchdoor timer, then initializes the instruction cache (instruction cache), initializes the stack and heap, initializes the block device copy function, and initializes the system clock and phase-locked loop. Next, according to the jumper setting of our OM pin on the board, BL0 uses the block device copy function to copy a code (BL1, the maximum code cannot exceed 16KB) from the corresponding external storage device to the SRAM inside the SoC, and then verify its checksum. If the checksum is correct, jump to the starting address of the BL1 code in the SRAM to execute. If it is checked and incorrect, jump to the second startup mode to start, and then step 5.

(2) the code of BL1 continues to read the remaining startup configuration code BL2 from the external storage device (this code cannot exceed 80KB at most, because the maximum of SRAM is 96KB and the maximum 16KB of BL1), and then jump to the code of BL2 to execute.

(3) BL2 this code first initializes the memory DRAM (DRAM can not be used directly after power-on, it needs to be initialized), and then read the code stored in the external storage device (external memory) about OS (operating system) initialization to DRAM (memory) to perform operating system initialization. After initialization is complete, you can start the operating system in memory and operate. Ps: memory said: it's finally my turn to play, .

(4) the external storage device (external memory) here can only be used after initialization. Here, initialization should be performed when BL0 uses the block device function to copy BL1 from external memory. Otherwise, you will not be able to read information from external memory.

(5) the process mentioned above is the process when the first startup mode is successful. If the first startup mode is not successful, then S5PV210 will jump to the second boot mode to start. The first boot mode can choose which external memory to boot from through the OM pin, while the second boot mode is fixed from channel 2 of the SD card. The specific implementation method is similar to the first startup mode above, except that the external memory media has been changed and is still carried out from step 2. As shown in the figure:

(6) if the second startup mode, that is, SD card channel 2, fails to start, jump to UART to start, and UART fails, then jump to USB mode to start, no more, GG. Good. It's already a brick.

5. Doubt:

(1) Why separate BL1 from BL2 and execute them in SRAM? Doesn't 96KB happen to include BL1 and BL2?

I heard a teacher say that because BL0 is not strong enough to initialize external memory, because IROM itself is only 64KB, there is no way to do too much. Only BL1 parts that read out-of-memory can be initialized. Then initialize the external memory through BL1, and then read the BL2 to execute.

(2) BL1 fixed 16KB? BL2 fixed 80KB?

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.