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Writing wrong (or corrupted) firmware to EEPROM will bring the USB FX2 microcontroller to stall. To bring it back out of a stall, the firmware recovery procedure differs upon the host operating system:
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Recovery Boot
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Configurations that put firmware into external memory thus need a second stage loader. For typical "flat" memory architectures, a loader supporting the 0xA3 vendor request is used to write into that memory. Similarly, a second stage loader that supports the 0xA2 or 0xA9 vendor request is needed when writing boot firmware into an I2C EEPROM. These 0xA2, 0xA9 and 0xA3 vendor commands are conventions defined by Cypress.
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Implicit Two-Step
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Recovery boot ≈
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Explicit Two-Step
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Recovery Boot
It is possible to write in EEPROM only using a 2nd stage loader firmware supporting EEPROM programming (aka intermediate good firmware) running in RAM; normally the bootloader Vend_Ax.hex is used.
- In the case of (implicit two-step) recovery boot (at this time, only Windows) the 2nd stage (boot)loader firmware is loaded without the explicit intervention of the user.
- In the case of (explicit two-step) recovery boot (mainly Linux) the 2nd stage (boot)loader firmware is loaded with the explicit intervention of the user.
Both recovery boots use exactly the same procedure (under the hood, they are one and the same), but in Windows OS case the 2nd stage (boot)loader firmware step is hidden/implicit in loadEEPROM() function used by CyConsole, CyControl and OpenFutNet.
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