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AT91SAM7 firmware for RC632 based reader.
0. Architecture
We have a Philips CL RC632 connected via SPI to the AT91SAM7.
The AT91SAM7 has a USB device port that is connected to a USB host.
1. USB Protocol / Interface
The AT91SAM7 has four USB endpoints, of which one is used for the control pipe,
and three are available for the user application.
Ideally, the device will provide two configurations, each with one interface
providing three endpoints: IN, OUT, INTERRUPT.
2. Interface configurations
2.1 Dumb interface
In this mode, the AT91SAM7 acts as a stupid interface between SPI and USB. It
provides access to the following primitives:
- Write Register
- Read Register
- Write FIFO
- Read FIFO
- Signal Interrupt
Since the FIFO of the RC632 are only 64byte deep, and the USB latency is too
big to facilitate FIFO refill while transmit, esp. at 424/848kbps RFID bitrate,
the AT91SAM7 has to provide bigger 'virtual' FIFO buffers to the USB host.
Thus, the USB host can fill a 1024byte-sized buffer using multiple USB packets,
and then ask the AT91SAM7 to write the first 64bytes to the FIFO. The RC632
will be programmed by the USB host to generate FIFO Level interrupts, to which
the AT91SAM7 will react automatically and re-fill the RC632 FIFO until all host
data has been sent to the RC632.
For the FIFO RX path, the opposite pattern is used: The AT91SAM7 has a 1024 byte
sized buffer, into which data can be read from the FIFO.
2.2 Intelligent interface
This interface will be optionally implemented at some later point. It provides
a 14443 protocol implementation inside the AT91SAM7.
2. Interface configurations
2.1 Dumb interface
EP0 control
EP1 bulk in
EP2 bulk out
EP3 interrupt
3. USB Protocol
3.1 dumb interface
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