From c72e4fcd4a77354d0d427cef263ebe438aeeae6e Mon Sep 17 00:00:00 2001 From: Megan Wachs Date: Tue, 24 Jan 2017 16:00:53 -0800 Subject: Add atomic bit-banging to the demo --- software/demo_gpio/demo_gpio.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) (limited to 'software') diff --git a/software/demo_gpio/demo_gpio.c b/software/demo_gpio/demo_gpio.c index c780cbe..040d864 100644 --- a/software/demo_gpio/demo_gpio.c +++ b/software/demo_gpio/demo_gpio.c @@ -7,6 +7,7 @@ #include "plic_driver.h" #include "encoding.h" #include +#include "stdatomic.h" #define RTC_FREQUENCY 32768 @@ -95,6 +96,8 @@ const char * instructions_msg = " \ SiFive E-Series Software Development Kit 'demo_gpio' program.\n\ Every 1.5 second, the Timer Interrupt will invert the LEDs.\n\ (Arty Dev Kit Only): Press Buttons 0, 1, 2 to Set the LEDs.\n\ +Pin 19 (HiFive1) or A5 (Arty Dev Kit) is being bit-banged\n\ +for GPIO speed demonstration.\n\ \n\ "; @@ -208,6 +211,9 @@ int main(int argc, char **argv) GPIO_REG(GPIO_OUTPUT_VAL) |= (0x1 << BLUE_LED_OFFSET) ; GPIO_REG(GPIO_OUTPUT_VAL) &= ~((0x1<< RED_LED_OFFSET) | (0x1<< GREEN_LED_OFFSET)) ; + // For Bit-banging with Atomics demo. + GPIO_REG(GPIO_OUTPUT_EN) |= (0x1 << PIN_19_OFFSET); + /************************************************************************** * Set up the PLIC * @@ -219,8 +225,17 @@ int main(int argc, char **argv) reset_demo(); - while (1){ + /************************************************************************** + * Demonstrate fast GPIO bit-banging. + * One can bang it faster than this if you know + * the entire OUTPUT_VAL that you want to write, but + * Atomics give a quick way to control a single bit. + *************************************************************************/ + uint32_t mask = (1 << PIN_19_OFFSET); + uint32_t other_mask = (1 << PIN_19_OFFSET); + while (1){ + atomic_fetch_xor(&GPIO_REG(GPIO_OUTPUT_VAL), mask); } return 0; -- cgit v1.2.1-18-gbd029