Electronic – How FPGA firmware writes in flash

flashfpgaspi

In some boards, like Papilio, spi flash connected only to fpga. As I can understand the firmware writes to flash through fpga. How does it works? Doesnt fpga need firmware first to work? If so, how it goes through fpga before any firmware was written in flash?

Best Answer

First of all, the whole point of JTAG is that it allows test software to manipulate the pins of the device in order to test their external connections to other devices on the board. The ability to manipulate the internal state of the device is a secondary function. So, it should be obvious that it will be possible to cause the pins to execute the protocol required to write data to the flash.

However, that tends to be rather slow in practice, because of the large number of JTAG transactions required to perform a single flash write. Therefore, most development systems download a small, fixed design to the FPGA whose only purpose is to write to the flash, and then they transfer the configuration data to it using a more efficient protocol (still over the JTAG interface).

Related Solutions

Electronic – Can’t write more than one byte to the SST39SF010A Flash!

Problem solved and I would like to share the solution:

Software Data Protection

This feature is available on some flashes that requires a software sequence at the beginning of each write cycle in order for a write to be performed. To enable the software data protection feature, a series of three-write commands to specific addresses with specific data must be performed. Once set, the same 3-byte code must begin each write request. This feature is permanently enabled in the flash I'm using.

So the solution is to add the following commands before any byte write operation not only the first one:

    * flash_addr1 = 0xaa;    
    * flash_addr2 = 0x55;
    * flash_addr3 = 0xa0;

Electronic – FATFS porting on STM32F103 SPI Flash

FATFS is a bad choice to use directly on a flash chip without any intermediate translation layer, as writing the FAT will overwrite the same sector again and again, causing these cells to wear out quickly.

You cannot reliably determine whether a certain block has been erased. If it reads back as only ones, the chance is fairly high that this is an empty, usable block, but it could also be a block that was in the process of being erased when the power went out, so some of the bits might be unstable. A flash file system should be aware of this, and explicitly mark blocks it has successfully erased with a specific marker.
The only way to be sure is to either perform an erase immediately before, or to have a note somewhere that a certain block has been erased.
You will erase the entire block, which contains 8 sectors. If any of these sectors already contains data, it will be erased as well, which you want to avoid.

As said, FAT is not suitable for use in this way.

Best Answer

Related Solutions

Electronic – Can’t write more than one byte to the SST39SF010A Flash!

Electronic – FATFS porting on STM32F103 SPI Flash

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