Gpio_out_xor

HiFive1 Rev B
1

GPIO_REG(GPIO_IOF_SEL) |= ( (1 << GREEN_LED_OFFSET) | (1 << BLUE_LED_OFFSET) | (1 << RED_LED_OFFSET));
GPIO_REG(GPIO_IOF_EN ) |= ( (1 << GREEN_LED_OFFSET) | (1 << BLUE_LED_OFFSET) | (1 << RED_LED_OFFSET));
GPIO_REG(GPIO_OUTPUT_XOR) &= ~( (1 << GREEN_LED_OFFSET) | (1 << BLUE_LED_OFFSET));
GPIO_REG(GPIO_OUTPUT_XOR) |= (1 << RED_LED_OFFSET);

what does it mean? (last two lines) can some one explain?

2

Have you read chapter 11 of the E300 Platform Reference Manual? Although to be fair there isn’t a lot of tutorial material there. I guess it assumes familiarity with other microcontrollers.

I believe the GPIO_OUTPUT_XOR register should toggle any GPIO pin whose bit it set to 1 when a write is made to the register.

In which case those last two lines look like a bug. I don’t know what is supposed to happen if you read from that register. Maybe it should be:

GPIO_REG(GPIO_OUTPUT_XOR) =  (1 << GREEN_LED_OFFSET) | (1 << BLUE_LED_OFFSET);
GPIO_REG(GPIO_OUTPUT_XOR) = (1 << RED_LED_OFFSET);

Which could be combined into one assignment, after initial set up.

3

Yeah I read.yes i understood !Well ,the information was good and helpful and i feel that i should improve my understanding over micro controllers.Anyways thank you.

4

A lot of the ARM microcontrollers have individual “set” and “clear” registers that let you do things like…

GPIO_REG(GPIO_OUTPUT_CLEAR) =  (1 << GREEN_LED_OFFSET) | (1 << BLUE_LED_OFFSET);
GPIO_REG(GPIO_OUTPUT_SET) = (1 << RED_LED_OFFSET);

… to turn off the green and blue LED’s GPIOs and turn on the red LED’s GPIO without having to read the whole IO register to a CPU register, turn bits on and off, and write the new value back.

We don’t seem to have that, but I guess the XOR register will often allow the same kind of things, possibly even with slightly less code if you implicitly already know the previous state.
.

5

As opposed to reserving special differently-addressed memory regions for atomic set and clear of device bits (bit banding), the RISC-V amoor and amoand instructions allow you to set and clear bits in a memory-mapped device with a single instruction using the normal device address. Amoxor lets you toggle the bits as described by Bruce.

1 Like
6

great!

7

should we connect IOREF 3v or 5v J1 jumper to use the digital pins?
and if so, can i use F-F jumper wire instead? i dont have the jumper pin.

8

That depends what voltage peripherals you want to connect.

It doesn’t matter what kind of wire you use to connect the pins as long as there is electrical continuity.

9

Okay then.
Thank you Bruce.