UM0290 datasheet(47/76 Pages) STMICROELECTRONICS

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UM0290

Mass storage demo

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5.3.4

Standard request requirements

To be compliant with the BOT specification the device must respond to the two following

requirements after receiving same standard requests:

●

When the device switches from unconfigured to configured state, the data toggle of all

endpoints

must

cleared.

This

requirement

served

the

function

Mass_Storage_SetConfiguration()

in the file usb_prop.c.

●

When the host sends a CBW command with invalid signature or invalid length, the

device must keep both endpoints 1 and 2 as STALL until receiving the Mass Storage

Reset class specific request. This functionality is managed by the function

Mass_Storage_ClearFeature()

in the file usb_prop.c.

5.3.5

BOT state machine

To provide the BOT protocol, a specific state machine is implemented with 5 states,

described below:

●

BOT_IDLE: this state is the default state after a USB Reset, BOT Mass storage Reset

or after sending a CSW. In this state the device is ready to receive a new CBW from the

host.

●

BOT_DATA_OUT: the device enters this state after receiving a CBW with data flow

from the host to the device.

●

BOT_DATA_IN: the device enters this state after receiving a CBW with data flow from

the device to the host

●

BOT_DATA_IN_LAST: the device moves to this state when it has to send the last part

of data asked for by the host.

●

BOT_CSW_SEND: the device moves to this state when it has to send the CSW. When

the device is in this state and a correct IN transfer occurs, the device moves to the

BOT_IDLE state to be able to receive the next CBW.

●

BOT_ERROR: Error state

The management of this state machine is done using the functions described below (files

usb_bot.c and usb_bot.h in the firmware):

●

Mass_Storage_In (); Mass_Storage_Out (): these two functions are called when a

correct transfer (IN or OUT) occurs. The aim of these two functions is to provide the

next step after receiving/sending a CBW, data or CSW

●

CBW_Decode (): this function is used to decode the CBW and to dispatch the firmware

to the corresponding SCSI command

●

DataInTransfer (): this function is used to transfer the characteristic device data to the

host

●

Set_CSW (): this function is used to set the CSW fields with the needed parameters

according to the command execution

●

Bot_Abort (): this function is used to STALL the endpoints 1 or 2 (or both) according to

the Error occurring in the BOT flow

Note:

The BOT state machine is the same for the two transfer modes (simple and double buffer

mode). The difference is only related on the data transfer (managed by the function

Send_Data () in the double buffer mode).

UM0290 Datasheet(PDF) 47 Page - STMicroelectronics

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