ST AN1527 Application note
AN1527
APPLICATION NOTE
DEVELOPING A USB
SMARTCARD READER WITH ST7SCR
by Microcontroller Division Applications
INTRODUCTION
This document desc ribes a firmware implementation dev eloped by ST Microelectron ics for a
USB Smart Card R ea der. Thi s fi rmwa re is f or the ST7S CR microc ontrol ler and can be us ed
with the associated Smart Card Reader board available from STMicroelectronics.
It is divided into 4 parts:
– Universal Serial Bus (USB) management: This is the USB library which manages the USB
hardware.
– Chip Card Interface Device (CCID) implementation: This contains high level functions for us-
ing the USB in compliance with CCID specifications (messages for Bulk-in, Bulk-out, interrupt and class requests)
– Interface Device (IFD) implementation: This contains high level functions for ISO 7816 spec-
ification implementation and the smartcard-specific command interpreter.
– 7816 UART Smartcard Interface (CRD) management: T his contains low level functions for
the hardware management of the 7816 UART Smartcard Inter face (C RD).
The main loop polls USB transactions (functions in Ccid_usb. c) using a state machine
process:
– USB_Polling() function from library for USB low level and endpoint 0 management.
– Receive USB Bulk-out message (CCID part).
– Execute the function corresponding to the Bulk-out message (IFD part).
– Send USB interrupt in message (CCID part) if necessary.
– Send USB Bulk-in response (CCID part).
The Bulk-out/in messages are managed by a state machi ne. When the Bulk-out message reception is completed, the message function is executed and returns only after the c ompletion
of the action to be done in the IFD part. As this may take several 10 ms (e.g. ATR reading), the
response is sent to the host by Bulk- in messa ge. The Bulk-i n/out messa ges are rece ived in
several transactions with a single transaction at every main loop i f the USB endpoint is available.
If there are any interrupt messages, they are sent just before the Bulk-in message is sent.
Specific CCID class requests are managed by the setup management function in the USB li-
brary (USER_USB_setup() function).
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1 CCID IMPLEMENTATION
1.1 GENERALITIES
The Chip Card In terface Device (CCID) f irmwar e implem entation c onforms to the “Uni versal
Serial Bus Device Class Specification for USB Chip/Smart Card Interface Devices” revision
1.0. It contains two files:
– Ccid_usb.c: This file contains the USB - CCID interface functions used to manage the state
machine that generates Bulk-in/Bulk-out messages.
– Ifd_ccid.c: This file contains the PC_to_RDR_xxx() and RDR_to_PC_xxx() message func-
tions for the CCID.
The following commands are not supported but can be added easily:
– PC_To_RDR_Secure,
– PC_To_RDR_SetDataRateAndClockFrequency,
– PC_To_RDR_ToAPDU,
– PC_To_RDR_Mechanical.
This CCID part uses a 271-byte buffer for all messages. Messages are composed of two
parts:
– header (10 bytes: fixed size)
– data (up to 261 bytes).
The size is based on the largest message managed at the short APDU transaction level. Due
to this large size, the ST7S CR can h ave o nly 1 buffe r and cannot s tore more than on e mes sage at a given time.
The CCID _Bu lkOu tMes sage( ) f unctio n u ses sever al B ulk-ou t U SB tr ansac tions to ver ify the
message header and store the entire message in the buffer.
When the message reception is comp leted, the C CID_DispatchMessage() function identifies
the message type and calls the corresponding function (PC_to_RDR_xxx()) for processing.
Then, the IFD par t of the firmw are execut es a c ommand on the ICC if nec essary. This com mand is included in the data field of the buffer. The PC_to_RDR_xxx() function receives from
the IFD the answer to the messag e in the buffer data field and returns an error code to be included in the Bulk-in response.
The RDR_to_PC_xxx() functi on, whic h corres ponds to the PC_to_RDR_x xx() previous ly executed, is launched and enters the correct values for error and status codes in the header.
At this time, the Bulk-in message is ready to be sent. But before the sending, the
CCID_IntMessage() function is executed to detect any hardw are problems or if a slot change
has occurred. In this case, the corresponding interrupt message is sent to the host.
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To finish the main loop, the CCID_BulkInMessage() function sends the Bulk-in message as an
answer to the previous Bulk-out message. The message is sent in a process that requires several Bulk-in transactions (same concept as for the Bulk-out process).
In addition, the Abort request is implemented through the CCIDClass RequestAbort() function
called in the USB_Polling() function. For this purpose, the USB_Polling() function is called in
the PC_to_RDR_xxx() function. When this request is received from endpoint 0, a flag is set
and the command sequence number is memorized.
All commands are aborted until the next PC_to_RDR_Abort command with the correct sequence number is received.
1.2 FUNCTION DESCRIPTION
■ void CCID_Init(void)
This function initializes the flags and status variables for the state machine process.
■ void CCID_Init_IT(void)
This function initializes the state machine and switches off the VccCard after a USB reset
done by the PC Host. It can only be called by an interrupt routine.
■ void CCID_Susp e nd_IT(void)
This function initializes the state machine and the card interface hardware after a resume from
USB suspend mode.
■ void CCID_BulkOutMessage(void)
This function manages the state machine during USB Bulk Out message reception. It fills the
message buffer with a maximum of 2 71 bytes.
■ void CCID_BulkInMessage(void)
This func tio n ma nag es the s tate mac hin e duri ng the USB Bu lk In m ess age tr an smiss ion . It
sends the buffer content as a message with a maximum of 271 bytes.
■ void CCID_DispatchMessage(void)
This function identifies the USB Bulk Out received message and c alls the corresponding func tions to process it : PC_to_RDR_xxx() and RDR_to_PC_xxx().
■ void CCID_IntMessage( void )
This function verifies the slot status and sends an interrupt In message if needed.
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■ void CcidClassRequestAbort(void)
This function is called from the USER_USB_Setup() function to process an Abort request.
■ unsigned char PC_to _ RDR_IccPowerOn(void)
This fu nction v erifies the PC_ TO_R DR_IC CPOW ERON c omman d form at and cal ls the
IFD_IccPowerOn() function (from Interface Device level). If IFD_IccPowerOn() returns no
error, the message header is filled with the ATR length. This PC_to_RDR function returns an
error code.
■ unsigned char PC_to _ RDR _ IccPowerOff(void)
This functi on ver ifies the P C_TO_R DR _IC CPO WE ROF F com mand fo rm at, switc hes o ff the
smartcard power supply and returns the NOERROR code.
■ unsigned char PC_to _ RDR_GetSlotStatus(void)
This functi on v eri fies t he PC_TO_RDR_GETSLOTSTATUS command fo r mat, v eri fies t he slot
hardware state and returns the corresponding error code.
■ unsigned char PC_to _ RDR _ Xf rB lock(void)
This function verifies the PC_TO_RDR_XFRBLOCK command format, checks the slot status
and returns an error if needed. If there is no error, it calls the IFD_XfrBlock() function (from the
Interface Device level). The message buffer contains the data to be transferred and is updated
by this IFD function. This PC_to_RDR function returns an error code.
■ unsigned char PC_to_RDR_GetParameters(void)
This function verifies the PC_TO_RDR_GETPARAM ETERS command format , checks the
slot hardware state and returns the corresponding error code.
■ unsigned char PC_to_RDR_ResetParameters(void)
This function verifies the PC_TO_RDR_RESETPARAMETERS command format, fills the
message buffer with the default values of the reader parameters and calls the
IFD_SetParameters() function (from the Interface Device level). This PC_to_RDR function returns an error code.
■ unsigned char PC_to_RDR_Set Parameters(void)
This function verifies the PC_TO_RDR_SETPARAMETERS command format and calls t he
IFD_SetParameters() function (from the Interface Device level). This PC_to_RDR function returns an error code.
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■ unsigned char PC_to_RDR_Escape(void)
This function verifies the PC_TO_RDR_ESCAPE command format and calls the
IFD_Escape() function (from t he Inter face Device lev el) . Thi s PC_to_RDR func tion retur ns an
error code (from IFD_Escape(), for example).
■ unsigned char PC_to_RDR_IccClock(void)
This function verifies the PC_TO_RDR_ICCCLOCK command format and calls the
IFD_SetClock() function (from the Interface Device level). This PC_to_RDR function returns
an error code (from IFD_SetClock(), for example).
■ unsigned char PC_to_RDR_Abort(void)
This function verifies the PC_TO_RDR_ABORT command format, checks the abort conditions and sets the corresponding flag. It returns the corresponding error code.
■ void RDR_to_PC_DataBlock(unsigned char ErrorCode)
This function fills the whole command buffer header including the error code given as input to
prepare the RDR_TO_PC_DATABLOCK message.
■ void RDR_to_PC_SlotSt atus(uns igned char ErrorCode)
This function fills the whole command buffer header including the error code given as input to
prepare the RDR_TO_PC_SLOTST ATUS message.
■ void RDR_to_PC_Parameters(unsigned char ErrorCode)
This function fills the whole command buffer header including the error code given as input to
prepare the RDR_TO_PC_PARAMET ERS message and call the IFD_GetParameters() function to fill the message data field.
■ void RDR_to_PC_Escape(unsigned char ErrorCode)
This function fills the whole command buffer header including the error code given as input to
prepare the RDR_TO_PC_ESCAPE message.
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