UM0290 datasheet(49/76 Pages) STMICROELECTRONICS

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UM0290

Mass storage demo

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5.3.7

Memory management

All the memory management functions are grouped in the two files: memory.c and

memory.h. The memory management consists of two basic processes:

●

Management and the validation of the address range for the command Read (10) and

Write (10): this process is done by the function Address_Management_Test(). The

role of this function is to extract the real Address and memory offset in the Medium

Memory Area and test if the current transfer (Read or Write) is in the memory range. If

this is not the case, the function STALLs endpoint 1 or both endpoints (depending on

whether the transfer is Read or Write) and returns a bad status to disable the transfer

●

Management of the Read and Write processes: this process is done by the two

functions Read_Memory() and Write_Memory(). These two functions manage the

medium memory access. After each access, the current memory offset and the next

Access Address are updated using the length of the previous transfer.

Note:

For the STR91x the read and write transfer from/to PMA is managed by the two functions

PMA_Read() and PMA_Write() (file usb_rw.c). This two functions are optimized to speed up

the transfer of data packets with a size multiple of 32 bits (4 bytes).

5.4

How to customize the mass storage demo

The implemented firmware is a simple example used to demonstrate the STR USB IP

capability in bulk transfer. However it can be customized according to user requirements.

This customization can be done in the three layers of the implemented mass storage

protocol:

●

Customization of the BOT layer: the user can implement their own BOT state

machine or modify the implemented one just by modifying the two files usb_BOT.c and

usb_BOT.h and by keeping the same data transfer method.

●

Customization of the SCSI layer: the implemented SCSI protocol presents, more

than the supported command listed in Section 5.3.6: SCSI protocol implementation, a

list of unsupported commands. When the host sends one of these commands, a

corresponding function is called by the CBW_Decode() function like a common

command. However, all the functions related to an unsupported command are defined

the

function

SCSI_Invalid_Cmd()

(see

file

usb_scsi.c).

The

SCSI_Invalid_Cmd()

function STALLs the two endpoints (1 and 2), sets the Sense

data to invalid command key and sends a CSW with a Command Failed status. If a

user wants to support one of the previous commands they have to comment-out the

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