115 lines
3.4 KiB
Plaintext
115 lines
3.4 KiB
Plaintext
Kernel driver for the NXP Semiconductors PN544 Near Field
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Communication chip
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Author: Jari Vanhala
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Contact: Matti Aaltonen (matti.j.aaltonen at nokia.com)
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General
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-------
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The PN544 is an integrated transmission module for contactless
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communication. The driver goes under drives/nfc/ and is compiled as a
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module named "pn544". It registers a misc device and creates a device
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file named "/dev/pn544".
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Host Interfaces: I2C, SPI and HSU, this driver supports currently only I2C.
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The Interface
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-------------
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The driver offers a sysfs interface for a hardware test and an IOCTL
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interface for selecting between two operating modes. There are read,
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write and poll functions for transferring messages. The two operating
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modes are the normal (HCI) mode and the firmware update mode.
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PN544 is controlled by sending messages from the userspace to the
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chip. The main function of the driver is just to pass those messages
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without caring about the message content.
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Protocols
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---------
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In the normal (HCI) mode and in the firmware update mode read and
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write functions behave a bit differently because the message formats
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or the protocols are different.
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In the normal (HCI) mode the protocol used is derived from the ETSI
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HCI specification. The firmware is updated using a specific protocol,
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which is different from HCI.
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HCI messages consist of an eight bit header and the message body. The
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header contains the message length. Maximum size for an HCI message is
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33. In HCI mode sent messages are tested for a correct
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checksum. Firmware update messages have the length in the second (MSB)
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and third (LSB) bytes of the message. The maximum FW message length is
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1024 bytes.
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For the ETSI HCI specification see
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http://www.etsi.org/WebSite/Technologies/ProtocolSpecification.aspx
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The Hardware Test
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-----------------
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The idea of the test is that it can performed by reading from the
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corresponding sysfs file. The test is implemented in the board file
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and it should test that PN544 can be put into the firmware update
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mode. If the test is not implemented the sysfs file does not get
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created.
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Example:
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> cat /sys/module/pn544/drivers/i2c\:pn544/3-002b/nfc_test
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1
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Normal Operation
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----------------
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PN544 is powered up when the device file is opened, otherwise it's
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turned off. Only one instance can use the device at a time.
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Userspace applications control PN544 with HCI messages. The hardware
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sends an interrupt when data is available for reading. Data is
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physically read when the read function is called by a userspace
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application. Poll() checks the read interrupt state. Configuration and
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self testing are also done from the userspace using read and write.
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Example platform data:
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static int rx71_pn544_nfc_request_resources(struct i2c_client *client)
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{
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/* Get and setup the HW resources for the device */
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}
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static void rx71_pn544_nfc_free_resources(void)
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{
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/* Release the HW resources */
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}
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static void rx71_pn544_nfc_enable(int fw)
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{
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/* Turn the device on */
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}
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static int rx71_pn544_nfc_test(void)
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{
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/*
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* Put the device into the FW update mode
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* and then back to the normal mode.
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* Check the behavior and return one on success,
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* zero on failure.
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*/
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}
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static void rx71_pn544_nfc_disable(void)
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{
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/* turn the power off */
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}
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static struct pn544_nfc_platform_data rx71_nfc_data = {
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.request_resources = rx71_pn544_nfc_request_resources,
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.free_resources = rx71_pn544_nfc_free_resources,
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.enable = rx71_pn544_nfc_enable,
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.test = rx71_pn544_nfc_test,
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.disable = rx71_pn544_nfc_disable,
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};
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