IO Functions

PRU↔Header pin mappings

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, similary 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()

Paramters

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()

Paramters

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 emp := receive_message();

if : emp >= 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);
}

R30 Register bit (Output)	R31 Register bit (Input)	Header pin
-	16	P1_20
7	7	P1_29
4	4	P1_31
1	1	P1_33
0	0	P1_36
-	15	P2_18
15	-	P2_33
-	14	P2_22
14	-	P2_24
6	6	P2_28
3	3	P2_30
2	2	P2_32
5	5	P2_34

R30 Register bit (Output)	R31 Register bit (Input)	Header pin
9	9	P1_02
11	11	P1_04
15	15	P1_30
14	14	P1_32
10	10	P1_35
-	16	P2_31
8	8	P2_35

R30 Register bit (Output)	R31 Register bit (Input)	Header pin
-	15	P8_15
15	-	P8_11
-	14	P8_16
14	-	P8_12
7	7	P9_25
5	5	P9_27
3	3	P9_28
1	1	P9_29
2	2	P9_30
0	0	P9_31
6	6	P9_41
4	4	P9_42

R30 Register bit (Output)	R31 Register bit (Input)	Header pin
13	13	P8_20
12	12	P8_21
8	8	**P8_27
10	10	**P8_28
9	9	**P8_29
6	6	**P8_39
7	7	**P8_40
4	4	**P8_41
5	5	**P8_42
2	2	**P8_43
3	3	**P8_44
0	0	**P8_45
1	1	**P8_46

R30 Register bit (Output)	R31 Register bit (Input)	Header pin
-	15	P8_15
15	-	P8_11
-	14	P8_16
14	-	P8_12
7	7	P9_25
5	5	P9_27
3	3	P9_28
1	1	P9_29
2	2	P9_30
0	0	P9_31
6	6	P9_41
4	4	P9_42

R30 Register bit (Output)	R31 Register bit (Input)	Header pin
1	1	P9_20
2	2	P9_19
3	3	P9_41
5	5	P8_18
6	6	P8_19
7	7	P8_13
9	9	P8_14
10	10	P9_42
11	11	P9_27
14	14	P9_14
15	15	P9_16
16	16	P8_15
17	17	P8_26
18	18	P8_16

R30 Register bit (Output)	R31 Register bit (Input)	Header pin
10	10	P8_33
11	11	P8_31
6	6	P8_38
7	7	P8_36
20	20	P8_08
15	15	P9_13
3	3	P8_39
2	2	P8_42
9	9	P8_35
8	8	P8_34
5	5	P8_37
4	4	P8_40
17	17	P8_28
18	18	P8_29
19	19	P8_30
1	1	P8_41
0	0	P8_44
14	14	P9_11

R30 Register bit (Output)	R31 Register bit (Input)	Header pin
0	0	P8_32
5	5	P9_25
6	6	P8_09
10	10	P9_31
8	8	P9_18
16	16	P8_07
15	15	P8_10
17	17	P8_27
20	20	P8_43
18	18	P8_45
19	19	P8_46
9	9	P9_17
13	13	P9_28
11	11	P9_29
12	12	P9_30