2/14

DEVELOPING A USB SMARTCARD READER WITH ST7SCR

1 CCID IMPLEMENTATION

1.1 GENERALITIES

The Chip Card Interface Device (CCID) firmware implementation conforms to the “Universal

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 ST7SCR can have only 1 buffer and cannot store more than one mes-

sage at a given time.

The CCID_BulkOutMessage() function uses several Bulk-out USB transactions to verify the

message header and store the entire message in the buffer.

When the message reception is completed, the CCID_DispatchMessage() function identifies

the message type and calls the corresponding function (PC_to_RDR_xxx()) for processing.

Then, the IFD part of the firmware executes a command on the ICC if necessary. 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 message in the buffer data field and returns an error code to be in-

cluded in the Bulk-in response.

The RDR_to_PC_xxx() function, which corresponds to the PC_to_RDR_xxx() previously exe-

cuted, 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. B ut before the sending, the

CCID_IntMessage() function is executed to detect any hardware problems or if a slot change

has occurred. In this case, the corresponding interrupt message is sent to the host.

2