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#include <stdint.h>
/*
* Function (or really pointer to code) for the reset interrupt handler.
*/
void on_reset(void);
/*
* Function which delays for a bit.
*/
void delay(void);
/* Type def to a void function to make things mor ereadable. */
typedef void (*isr_routine)(void);
/* Gpio configuration structure. This is exactly how it is laid out in
* memory. In these registers bit X referes to pin X. */
typedef struct {
/* The direction of the gpio pin. 1 = output, 0 = input. */
uint32_t dir;
/* The value of the gpio pin (for input). */
uint32_t in;
/* Write to set the output value for the pin. */
uint32_t out;
/* The clear value. Resets the pin to what it is at reset. */
uint32_t clr;
/* Sets the pin to be pull-up on logical 1 in input mode. */
uint32_t pu;
/* Sets whether the pin should be pull-down (open-drain) for logical 0 or
* drive for logical 1. 1 = pull-down, 0 = drive. */
uint32_t pd_drv;
} gpio_t;
/** The ISR Vector structure. This is linked to starting at address 0. */
__attribute((__section__(".isr_vector"))) volatile struct {
// What NULL points to. nothing useful.
uint32_t reserved__;
// Called when the device boots or reset is pressed.
isr_routine reset_cb;
isr_routine nmi_cb;
isr_routine exc_cb;
} isr_vectors = {.reset_cb = on_reset};
// GPIO configuration registers. These are defined in the linker script.
extern volatile gpio_t gpio_a;
extern volatile gpio_t gpio_b;
/* Main routine. This is called on_reset once everything else has been set up.
*/
static void start(void)
{
uint32_t bit = 1 << 8;
gpio_a.dir |= bit; // Set to "out"
gpio_a.pd_drv |= bit; // Set to "open drain"
for (;;) {
gpio_a.out &= ~bit; // Pin low (turns on LED)
delay();
gpio_a.out |= bit; // Pin high (turns off LED)
delay();
}
}
/*
* The reset callback.This has to be a naked function because the stack pointer
* may not be initialized!!.
*/
__attribute((naked)) void on_reset(void)
{
// Set up the stack pointer to point to the end of SRAM.
asm volatile(
"li sp,0x20008000\n"
"addi sp,sp,-4\n"
"jalr %0\n"
"spin:\n"
"j spin\n"
:
: "r"(start));
}
void delay(void)
{
for (volatile uint32_t i = 0; i < 20000; ++i)
;
}
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