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-rw-r--r--software/demo_gpio/demo_gpio.c54
1 files changed, 32 insertions, 22 deletions
diff --git a/software/demo_gpio/demo_gpio.c b/software/demo_gpio/demo_gpio.c
index dec91b5..00bc8cd 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 <unistd.h>
+#include "stdatomic.h"
#define RTC_FREQUENCY 32768
@@ -25,12 +26,6 @@ function_ptr_t g_ext_interrupt_handlers[PLIC_NUM_INTERRUPTS];
plic_instance_t g_plic;
-// Simple variables for LEDs, buttons, etc.
-volatile unsigned int* g_output_vals = (unsigned int *) (GPIO_BASE_ADDR + GPIO_OUTPUT_VAL);
-volatile unsigned int* g_input_vals = (unsigned int *) (GPIO_BASE_ADDR + GPIO_INPUT_VAL);
-volatile unsigned int* g_output_en = (unsigned int *) (GPIO_BASE_ADDR + GPIO_OUTPUT_EN);
-volatile unsigned int* g_pullup_en = (unsigned int *) (GPIO_BASE_ADDR + GPIO_PULLUP_EN);
-volatile unsigned int* g_input_en = (unsigned int *) (GPIO_BASE_ADDR + GPIO_INPUT_EN);
/*Entry Point for PLIC Interrupt Handler*/
void handle_m_ext_interrupt(){
@@ -60,12 +55,12 @@ void handle_m_time_interrupt(){
*mtimecmp = then;
// read the current value of the LEDS and invert them.
- uint32_t leds = *g_output_vals;
-
- *g_output_vals ^= ((0x1 << RED_LED_OFFSET) |
- (0x1 << GREEN_LED_OFFSET) |
- (0x1 << BLUE_LED_OFFSET));
+ uint32_t leds = GPIO_REG(GPIO_OUTPUT_VAL);
+ GPIO_REG(GPIO_OUTPUT_VAL) ^= ((0x1 << RED_LED_OFFSET) |
+ (0x1 << GREEN_LED_OFFSET) |
+ (0x1 << BLUE_LED_OFFSET));
+
// Re-enable the timer interrupt.
set_csr(mie, MIP_MTIP);
@@ -101,6 +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\
";
@@ -114,7 +111,7 @@ void print_instructions() {
void button_0_handler(void) {
// Red LED on
- * g_output_vals |= (0x1 << RED_LED_OFFSET);
+ GPIO_REG(GPIO_OUTPUT_VAL) |= (0x1 << RED_LED_OFFSET);
// Clear the GPIO Pending interrupt by writing 1.
GPIO_REG(GPIO_RISE_IP) = (0x1 << BUTTON_0_OFFSET);
@@ -124,7 +121,7 @@ void button_0_handler(void) {
void button_1_handler(void) {
// Green LED On
- * g_output_vals |= (1 << GREEN_LED_OFFSET);
+ GPIO_REG(GPIO_OUTPUT_VAL) |= (1 << GREEN_LED_OFFSET);
// Clear the GPIO Pending interrupt by writing 1.
GPIO_REG(GPIO_RISE_IP) = (0x1 << BUTTON_1_OFFSET);
@@ -135,7 +132,7 @@ void button_1_handler(void) {
void button_2_handler(void) {
// Blue LED On
- * g_output_vals |= (1 << BLUE_LED_OFFSET);
+ GPIO_REG(GPIO_OUTPUT_VAL) |= (1 << BLUE_LED_OFFSET);
GPIO_REG(GPIO_RISE_IP) = (0x1 << BUTTON_2_OFFSET);
@@ -204,16 +201,19 @@ int main(int argc, char **argv)
// can be used as both Inputs and Outputs.
#ifdef HAS_BOARD_BUTTONS
- * g_output_en &= ~((0x1 << BUTTON_0_OFFSET) | (0x1 << BUTTON_1_OFFSET) | (0x1 << BUTTON_2_OFFSET));
- * g_pullup_en &= ~((0x1 << BUTTON_0_OFFSET) | (0x1 << BUTTON_1_OFFSET) | (0x1 << BUTTON_2_OFFSET));
- * g_input_en |= ((0x1 << BUTTON_0_OFFSET) | (0x1 << BUTTON_1_OFFSET) | (0x1 << BUTTON_2_OFFSET));
+ GPIO_REG(GPIO_OUTPUT_EN) &= ~((0x1 << BUTTON_0_OFFSET) | (0x1 << BUTTON_1_OFFSET) | (0x1 << BUTTON_2_OFFSET));
+ GPIO_REG(GPIO_PULLUP_EN) &= ~((0x1 << BUTTON_0_OFFSET) | (0x1 << BUTTON_1_OFFSET) | (0x1 << BUTTON_2_OFFSET));
+ GPIO_REG(GPIO_INPUT_EN) |= ((0x1 << BUTTON_0_OFFSET) | (0x1 << BUTTON_1_OFFSET) | (0x1 << BUTTON_2_OFFSET));
#endif
- * g_input_en &= ~((0x1<< RED_LED_OFFSET) | (0x1<< GREEN_LED_OFFSET) | (0x1 << BLUE_LED_OFFSET)) ;
- * g_output_en |= ((0x1<< RED_LED_OFFSET)| (0x1<< GREEN_LED_OFFSET) | (0x1 << BLUE_LED_OFFSET)) ;
- * g_output_vals |= (0x1 << BLUE_LED_OFFSET) ;
- * g_output_vals &= ~((0x1<< RED_LED_OFFSET) | (0x1<< GREEN_LED_OFFSET)) ;
+ GPIO_REG(GPIO_INPUT_EN) &= ~((0x1<< RED_LED_OFFSET) | (0x1<< GREEN_LED_OFFSET) | (0x1 << BLUE_LED_OFFSET)) ;
+ GPIO_REG(GPIO_OUTPUT_EN) |= ((0x1<< RED_LED_OFFSET)| (0x1<< GREEN_LED_OFFSET) | (0x1 << BLUE_LED_OFFSET)) ;
+ 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
*
@@ -225,7 +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);
+
+ while (1){
+ atomic_fetch_xor_explicit(&GPIO_REG(GPIO_OUTPUT_VAL), mask, memory_order_relaxed);
+ }
return 0;