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6.

Accessing the Low level Flash Drivers

The AT90USB USB bootloader is located in the boot section of the on-chip flash memory, mean-

while the bootloader section is the unique memory location allowed to execute on-chip flash

memory write operations (SPM instruction is decoded only in this section).

Thus applications which require on-chip flash write access can perform calls to specific entry

points located in the USB bootloader.

The USB bootloader provides several Application Programming Interfaces (API) that allows the

application to access low level flash drivers located in the boot section. These APIs allow the fol-

lowing operations:

• Page Erase

• Page Write

• Load word in the temporary page buffer

Figure 6-1.

USB bootloader API calls

Application section

Boot section

API entry points

USB Bootloader

Low level flash drivers

On-Chip flash Request:

"Page Erase"

"Page Write"

"Load Word"

Low Level

Flash Operations

Target Page modified

Application