Class pn532::esp32::spi_channel

Defined in File spi.hpp

Inheritance Relationships

Base Type

public pn532::channel (Class pn532::channel)

Class Documentation

class spi_channel : public pn532::channel 

Implementation of SPI channel protocol for PN532 over ESP32’s SPI driver (UM0701-02 §6.2.5).

This class supports, when specified, the possibility of using a GPIO pin for the PN532’s IRQ line; in that case, the class does not have to poll the controller until the answers are ready, but it will instead idle and wait for the IRQ line to become active, and read the answer only then once it’s ready. That is done through a semaphore and an interrupt installed on the GPIO.

Note

This class supports a “stream-like” usage, i.e. it can progressively read pieces of an incoming info frame in order to determine its length. To achieve that, it is stateful (during a receive operation), as any receive operation other than the first has to omit specifying the data read prefix.

Warning

Experiments have shown that the SPI channel is often unstable, especially at high clocks (> 1MHz). It is not clear why this occurs, but it looks like at high speeds it fails when transmitting extended info frames. Even at low speeds, it seldom fails after long exchanges. The PN532 enters an invalid state in which it never returns an answer. Therefore it’s recommended to stay within 1MHz of speed.

Public Functions

virtual bool wake() override: Sends the byte sequence 55 55 55.

spi_channel(spi_host_device_t host, spi_bus_config_t const &bus_config, spi_device_interface_config_t device_cfg, spi_dma_chan_t dma_chan)

Construct an SPI channel for a PN532.

Note

In case of invalid host, device or bus configuration, an error message is printed, but the class is correctly constructed. It will simply always fail to send and receive anything (and may clog your output with error messages).

Parameters:

host – SPI Host to use. Note that on ESP32-S2 SPI1_HOST is not supported (as per ESP32’s documentation).
bus_config – SPI bus configuration.
device_cfg – SPI device configuration. Note that despite PN532 supporting up to 5MHz speed, the channel may be unstable and a lower speed (1MHz) is recommended.
dma_chan – The DMA channel to use for transmitting data. Note that DMA channel 0 is not supported (as per ESP32’s documentation), therefore it must be either DMA channel 1 or DMA channel 2.

spi_channel(spi_host_device_t host, spi_bus_config_t const &bus_config, spi_device_interface_config_t device_cfg, int dma_chan, gpio_num_t response_irq_line, bool manage_isr_service)

Construct an SPI channel for a PN532, using the given GPIO pin to signal when the answer is ready (IRQ line).

Using the IRQ line reduces the amount of noise on the line because it will only read the answer once it’s available.