eCos Reference Manual
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# Overview

## Name

Overview -- eCos Support for AMD AM29xxxxx Flash Devices and Compatibles

## Description

The `CYGPKG_DEVS_FLASH_AMD_AM29XXXXX_V2` AMD AM29xxxxx V2 flash driver package implements support for the AM29xxxxx family of flash devices and compatibles. Normally the driver is not accessed directly. Instead application code will use the API provided by the generic flash driver package `CYGPKG_IO_FLASH`, for example by calling functions like `cyg_flash_program`.

The driver imposes one restriction on application code which developers should be aware of: when programming the flash the destination addresses must be aligned to a bus boundary. For example if the target hardware has a single flash device attached to a 16-bit bus then program operations must involve a multiple of 16-bit values aligned to a 16-bit boundary. Note that it is the bus width that matters, not the device width. If the target hardware has two 16-bit devices attached to a 32-bit bus then program operations must still be aligned to a 32-bit boundary, even though in theory a 16-bit boundary would suffice. In practice this is rarely an issue, and requiring the larger boundary greatly simplifies the code and improves performance.

> Note: Many eCos targets with AM29xxxxx or compatible flash devices will still use the older driver package `CYGPKG_DEVS_FLASH_AMD_AM29XXXXX`. Only newer ports and some older ports that have been converted will use the V2 driver. This documentation only applies to the V2 driver.

## Configuration Options

The AM29xxxxx flash driver package will be loaded automatically when configuring eCos for a target with suitable hardware. However the driver will be inactive unless the generic flash package `CYGPKG_IO_FLASH` is loaded. It may be necessary to add this generic package to the configuration explicitly before the driver functionality becomes available. There should never be any need to load or unload the AM29xxxx driver package.

There are a number of configuration options, relating mostly to hardware characteristics. It is very rare that application developers need to change any of these. For example the option `CYGNUM_DEVS_FLASH_AMD_AM29XXXXX_V2_ERASE_REGIONS` may need a non-default value if the flash devices used on the target have an unusual boot block layout. If so the platform HAL will impose a requires constraint on this option and the configuration system will resolve the constraint. The only time it might be necessary to change the value manually is if the actual board being used is a variant of the one supported by the platform HAL and uses a different flash chip.

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