RM0319 datasheet(45/368 Pages) STMICROELECTRONICS

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RM0319

BootROM

Doc ID 022640 Rev 3

45/368

5.6.5

USB boot

USB boot refers to upgrading of Flash memories (NAND and NOR) via USB. In USB boot,

BootROM programs PLL1 to 333 MHz and system to Normal mode, for instance ARM

frequency at 333 MHz, initializes the USB Device Controller (UDC) and initializes USB state

machine to GET_CMD phase.

UDC supports 2 modes of operation, Slave mode and DMA mode, in SPEAr BootROM UDC

is configured in slave mode.

After initializing, BootROM waits for a 12 byte command on BULK Out End point 2 from the

USB Host, the format for 12 byte command is as follows:

After receiving 12 bytes, BootROM decodes 12 byte command, changes the USB state

machine to GET_DATA phase and waits for the expected number of bytes from the Host.

BootROM receives the data and stores it into the load address specified in the command,

once all the data is received, BootROM changes the USB state machine to EXEC phase

and decodes the type of data. If the received data is DDR Driver, then BootROM jumps to

load address, executes the DDR driver and jumps back to BootROM. Now that the DDR is

initialized, BootROM changes the USB state machine again to GET_CMD phase. Now

same process is repeated again, but this time type of data received is FIRMWARE, the

FIRMWARE is capable of receiving data from Host, Flash upgrade capable etc. After

receiving the FIRMWARE, BootROM jumps to it in DDR.

The current version of BootROM uses the slave mode, because of limitation of SPEAr

architecture i.e. there is no Path from UDC DMA to access descriptors present in eRAM.

Table 8.

Command format

Byte 0

Type of Data

Byte 1 - 3

RESERVED

Byte 4 - 7

Size of Data

Byte 8 - 11

Load Address in RAM

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