IO Functions#

All Header pins are constant integer variable by default, with its value equal to respective R30/R31 register bit
- Example: P1_20 is an constant integer variable with value 16, similarly P1_02 is an constant integer variable with value 9

Digital Write#

digital_write is a function which enables PRU to write given logic level at specified output pin. It is a function with void return type and it’s parameters are integer and boolean, first parameter is the pin number to write to or PRU R30 register bit and second parameter is boolean value to be written. true for HIGH and false for LOW.

Syntax#

digital_write(pin_number, value);

Parameters#

pin_number is an integer. It must be a header pin name which supports output, or PRU R30 Register bit.
value is a boolean. It is used to set logic level of the output pin, true for HIGH and false for LOW.

Return Type#

void - returns nothing.

Example#

int a := 32;

if : a < 32 {
    digital_write(P1_29, true);
}
else {
    digital_write(P1_29, false);
}

If the value of a < 32, then pin P1_29 is set to HIGH or else it is set to LOW.

Digital Read#

digital_read is a function which enables PRU to read logic level at specified input pin. It is a function with return type boolean and it’s parameter is a integer whose value must be the pin number to be read or PRU R31 register bit.

Syntax#

digital_read(pin_number);

Parameters#

pin_number is an integer. It must be a header pin name which supports input, or PRU R31 Register bit.

Return Type#

boolean - returns the logic level of the pin number passed to it. It returns true for HIGH and false for LOW.

Example#

if digital_read(P1_20) {
    digital_write(P1_29, false);
}
else {
    digital_write(P1_29, true);
}

Logic level of pin P1_20 is read. If it is HIGH, then pin P1_29 is set to LOW, or else it is set to HIGH.

Delay#

delay is a function which makes PRU wait for specified milliseconds. When this is called PRU does absolutely nothing, it just sits there waiting.

Syntax#

delay(time_in_ms);

Parameters#

time_in_ms is an integer. It is the amount of time PRU should wait in milliseconds. (1000 milliseconds = 1 second).

Return Type#

void - returns nothing.

Example#

digital_write(P1_29, true);
delay(2000);
digital_write(P1_29, false);

Logic level of pin P1_29 is set to HIGH, PRU waits for 2000 ms = 2 seconds, and then sets the logic level of pin P1_29 to LOW.

Start counter#

start_counter is a function which starts PRU’s internal counter. It counts number of CPU cycles. So it can be used to count time elapsed, as it is known that each cycle takes 5 nanoseconds.

Syntax#

start_counter()

Parameters#

n/a

Return Type#

void - returns nothing.

Example#

start_counter();

Stop counter#

stop_counter is a function which stops PRU’s internal counter.

Syntax#

stop_counter()

Parameters#

n/a

Return Type#

void - returns nothing.

Example#

stop_counter();

Read counter#

read_counter is a function which reads PRU’s internal counter and returns the value. It counts number of CPU cycles. So it can be used to count time elapsed, as it is known that each cycle takes 5 nanoseconds.

Syntax#

read_counter()

Parameters#

n/a

Return Type#

integer - returns the number of cycles elapsed since calling start_counter.

Example#

start_counter();

while : read_counter < 200000000 {
    digital_write(P1_29, true);
}

digital_write(P1_29, false);
stop_counter();

while the value of hardware counter is less than 200000000, it will set logic level of pin P1_29 to HIGH, after that it will set it to LOW. Here, 200000000 cpu cycles means 1 second of time, as CPU clock is 200 MHz. So, LED will turn on for 1 second, and turn off after.

Init message channel#

init_message_channel is a function which is used to initialise communication channel between PRU and the ARM core. It is sets up necessary structures to use RPMSG to communicate, it expects a init message from the ARM core to initialise. It is a necessary to call this function before using any of the message functions.

Syntax#

init_message_channel()

Parameters#

n/a

Return Type#

void - returns nothing

Example#

init_message_channel();

Receive message#

receive_message is a function which is used to receive messages from ARM to the PRU, messages can only be integers, as only they are supported as of now. It uses RPMSG channel setup by init_message_channel to receive messages from ARM core.

Syntax#

receive_message()

Parameters#

n/a

Return Type#

integer - returns integer data received from PRU

Example#

init_message_channel();

int temp := receive_message();

if : temp >= 0 {
    digital_write(P1_29, true);
}
else {
    digital_write(P1_29, false);
}

Send message#

There are six functions which are used to send messages to ARM core from PRU, messages can be integers, characters, bools, integer arrays, character arrays, and boolean arrays. It uses RPMSG channel setup by init_message_channel to send messages from PRU to the ARM core.

For sending arrays, arrays are automatically converted to a string, for example, [1, 2, 3, 4] would become “1 2 3 4”.

Syntax#

send_int(expression)
send_char(expression)
send_bool(expression)
send_ints(identifier)
send_chars(identifier)
send_bools(identifier)
send_message is an alias for send_int to preserve backwards compatibility.

Parameters#

For send_int and send_char, expression would be an arithmetic expression.
For send_bool, expression would be a boolean expression
For send_ints, identifier should be an identifier for an integer array.
For send_chars, identifier should be an identifier for a character array.
For send_bools, identifier should be an identifier for a boolean array.

Example#

init_message_channel();

if : digital_read(P1_29) {
    send_bool(true);
}
else {
    send_int(0);
}