What i got from this link is that -- STx7111 Mboard - have some serial port which is capable to communicate with GDB. And from GDB we use to burn following file u-boot. Is this file burned in RAM or NAND flash by gdb ?
No, you did not read that article accurately.
GDB is merely used as the interface to the JTAG.
This first step is to load an executable (a copy of U-Boot) into RAM.
Do every controller have some serial port which is capable to communicate with GDB ?
Do every controller follow this approach to burn uboot bootloader into its NAND flash ?
You should avoid making (or trying to make) sweeping generalizations (in this and your other postings).
The features and capabilities of microcontrollers, microprocessors and SoCs ("controllers" is something else) is so broad that very few generalization can be made. Rarely is there only "one way" to perform these procedures.
In order the write a copy of U-Boot (or any file image) to NAND flash, there are two steps:
transfer the image file from the host PC (or some storage device) into local memory;
erase the NAND flash blocks, and then write the image file to NAND flash with ECC if required and cognizant of bad blocks.
These are not trivial steps, so a capable utility is needed. There are at least three approaches:
The microcontroller can be configured (via input pins) to a "receive and write an image file" mode on power-up. A hardcoded program in ROM will load the image and write it to the integrated flash.
The SoC ROM has a bootloader that has capabilities to communicate with a host PC over RS232 or USB, and can perform as the client side of a proprietary utility program. On the host PC you would run the server side of this utility program. This scheme would allow transferring files and reading & writing the target's memories. Atmel's SAM-BA utility fits into this category.
Use an open-source utility, such as U-Boot, that is configurable and extensible to support the external NAND flash and any other memory types on your board, and also has file transfer capabilities. The console for U-Boot is typically a UART/USART serial port, but can be configured to use a USB-to-RS232 adapter.
In the case of using a program like U-Boot to install programs in NAND, a chicken versus egg situation arises: how to get this program loaded in the first place? The two common approaches are:
a. Install the utility (i.e. U-Boot) on a SDcard with any required bootloader, and then boot the SoC from the SDcard. This assumes that the SoC has this booting capability, but this scheme requires the least operator skill.
b. Load the utility (i.e. U-Boot) using JTAG, such as Segger J-Link, which will allow you to transfer the image file to RAM (assuming that RAM has been properly initialized if necessary) and then start its execution. The J-Link can be interfaced using its own JLINK program or GDB.
Once U-Boot is resident and executing, you have all of its capabilities available. U-Boot cannot write itself to NAND flash, so you have to load another copy of U-Boot in order to write it to NAND (or any other type of) flash.
