Class _spia: Serial Peripheral Interface

A class _spia object is a Serial Peripheral Interface. It has the following relatives:

• pin_mosi: the MOSI pin
• pin_miso: the MISO pin
• pin_sck: the SCK pin
• pin_ss: the SS pin

It is used by:

• ATmega48A/PA/88A/PA/168A/PA/328/P : spi0

Interrupts

Class _spia objects can trigger the following IRQs:

• spi0: transfer complete

Actions

configure:

Note 1 When configured in master or slave mode, the SPI automatically configures its related I/O pins as inputs or outputs according to the mode.

Note 2 In master mode, if the SS pin is configured as an input, it must be held high. Otherwise the SPI will be automatically turned into slave mode by hardware as soon as the SS pin goes low.

hwa( configure,       spi0,
 
     function,        master
                    | slave
                    | off,
 
     clock,           ioclk / (    2         //  Clock frequency
                               |   4
                               |   8
                               |  16
                               |  32
                               |  64
                               | 128 ),
 
   [ mode,            0 | 1 | 2 | 3, ]
 
   [ idle_state,      low                    //  State of SCK when idle
                    | high,
 
     sampling_edge,   falling                //  Sampling clock edge
                    | rising, ]
 
   [ data_order,      lsb_first
                    | msb_first ] );

read:

hw( read, spi0 );

write:

hw(_write, spi0, value );

turn: when the SPI is turned on, it takes control of the MOSI and MISO pins.

hw( turn, spi0, on | off );

hwa( turn, spi0, on | off );

stat: returns the collision flag:

hw_stat_t( spi0 ) st ;       //  Create a structure to receive the counter status
 
st = hw( stat, spi0 );       //  Copy the SPI status into the structure
 
if ( st.collision )          //  Process the collision flag
  n_collisions++ ;

Reading the "transfer complete" flag:

if ( hw( read, (spi0,irq) ) )        // Read "transfer complete" IRQ flag
  hw( disable, (spi0,irq) );         // Disable transfer complete IRQs

The "transfer complete" flag is cleared by hardware when the corresponding ISR is executed. It is also cleared when the SPI is read or written after the flag has been read:

if ( hw( read, (spi0,irq) ) )        // Read transfer complete IRQ flag
  data = hw( read, spi0 );           // Read data and clear transfer complete IRQ flag

Registers

Class _spia objects hold the following hardware registers:

• cr: control register
• sr: status register
• dr: data register

that hold the following logical registers:

• en: spi enable
• dord: data order
• mstr: master/slave
• cpol: clock polarity
• cpha: clock phase
• xpr: clock prescaler
• wcol: write collision
• sp2x: double clock speed
• ie: overflow interrupt mask
• if: overflow interrupt flag