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Found Macronix flash chip "MX25L3205" (4096 kB, SPI) on buspirate_spi.
Erasing and writing flash chip... Trying erase function 0... 0x000000-0x000fff:EERASE FAILED at 0x00000000! Expected=0xff, Read=0x00, failed byte count from 0x00000000-0x00000fff: 0x1000
ERASE FAILED!
Reading current flash chip contents... done. Looking for another erase function.
Trying erase function 1... 0x000000-0x000fff:EERASE FAILED at 0x00000000! Expected=0xff, Read=0x00, failed byte count from 0x00000000-0x00000fff: 0x1000
ERASE FAILED!
Reading current flash chip contents... done. Looking for another erase function.
Trying erase function 2... 0x000000-0x3fffff:EERASE FAILED at 0x00000000! Expected=0xff, Read=0x00, failed byte count from 0x00000000-0x003fffff: 0x400000
ERASE FAILED!
Reading current flash chip contents... done. Looking for another erase function.
Trying erase function 3... 0x000000-0x3fffff:EERASE FAILED at 0x00000000! Expected=0xff, Read=0x00, failed byte count from 0x00000000-0x003fffff: 0x400000
ERASE FAILED!
Looking for another erase function.
No usable erase functions left.
FAILED!
Your flash chip is in an unknown state.
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Any help or suggestion?

SPI Programmer:
Bus Pirate v3.a
Firmware v6.2-beta1 r1981  Bootloader v4.4

Cheers.