[FS#510] slow sysupgrade

[LEDE Bugs]

The following task has a new comment added:

FS#510 - slow sysupgrade
User who did this - Arjen de Korte (arjendekorte)

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Erase times don't depend on SPI clock frequency. The erase timing is determined by an internal timer in the flash device and there is no way to change that. The commands needed to start erasing are just one byte to enable write/erase and just four bytes to erase a block/sector. In relation to the erase times, this is negligible. The only way to speedup the erase process, is to use the largest erase size possible and to erase as little memory as possible.

The SPI clock has negligible influence on the boot times. At bootup, the contents of the SPI flash will be copied to RAM first and then the code runs from memory. A typical image is probably in the order of 4 Mbytes, which can be copied to RAM in just over a second, even at a SPI clock of just 25 MHz.
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=510#comment3416