fw: wrote a simple little hello world app in C

firmware/hello_world_c/.gitignore

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+*.elf
+*.bin

firmware/hello_world_c/Makefile

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+PREFIX := riscv64-unknown-elf-
+CC := $(PREFIX)gcc
+OBJCOPY := $(PREFIX)objcopy
+
+ARGS := -mabi=ilp32 -march=rv32im -ffreestanding -nostdlib -Wl,-Bstatic,-T,memory.ld,--strip-debug
+
+SOURCES := main.c
+INCLUDES := uart.h
+
+hello_world.bin: hello_world.elf
+	$(OBJCOPY) -S -O binary hello_world.elf hello_world.bin
+
+hello_world.elf: $(SOURCES) $(INCLUDES)
+	$(CC) $(ARGS) $(SOURCES) -o hello_world.elf
+
+clean:
+	rm -f hello_world.elf hello_world.bin

firmware/hello_world_c/main.c

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+#include "uart.h"
+
+#include <stdint.h>
+
+void write_cstring(const char* string);
+void write_char(char c);
+
+
+int main() {
+    for (;;) {
+        write_char('H');
+        write_char('e');
+        write_char('l');
+        write_char('l');
+        write_char('o');
+        write_char(' ');
+        write_char('W');
+        write_char('o');
+        write_char('r');
+        write_char('l');
+        write_char('d');
+        write_char('!');
+        write_char('\n');
+        write_char('\r');
+    }
+}
+
+
+void write_char(char c) {
+    while (!UART0->TXEMPTY);
+
+    // Wait for room to clear up
+    if (!UART0->TXFULL) {
+        UART0->RXTX = c;
+    }
+}
+void write_cstring(const char* string) {
+    int i = 0;
+
+    for (;;) {
+        // Return at end of string
+        if (string[i] == 0) {
+            return;
+        }
+
+        // Wait for room to clear up
+        if (!UART0->TXFULL) {
+            UART0->RXTX = string[i];
+        }
+
+        i += 1;
+    }
+
+}

firmware/hello_world_c/memory.ld

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+/* stolen from https://github.com/Obijuan/RISC-V-FPGA/blob/master/firmware/soc-demo/src-c/sections.lds */
+
+MEMORY
+{
+    ROM (rx)      : ORIGIN = 0x01000000, LENGTH = 0x1000 /* 4KiB */
+    RAM (xrw)       : ORIGIN = 0x01001000, LENGTH = 0x1000 /* 4KiB */
+}
+
+SECTIONS {
+    /* The program code and other data goes into FLASH */
+    .text :
+    {
+        . = ALIGN(4);
+        *(.text)           /* .text sections (code) */
+        *(.text*)          /* .text* sections (code) */
+        *(.rodata)         /* .rodata sections (constants, strings, etc.) */
+        *(.rodata*)        /* .rodata* sections (constants, strings, etc.) */
+        *(.srodata)        /* .rodata sections (constants, strings, etc.) */
+        *(.srodata*)       /* .rodata* sections (constants, strings, etc.) */
+        _etext = .;        /* define a global symbol at end of code */
+        _sidata = _etext;  /* This is used by the startup in order to initialize the .data secion */
+    } >ROM
+
+
+    /* This is the initialized data section
+    The program executes knowing that the data is in the RAM
+    but the loader puts the initial values in the FLASH (inidata).
+    It is one task of the startup to copy the initial values from FLASH to RAM. */
+    .data : AT ( _sidata )
+    {
+        . = ALIGN(4);
+        _sdata = .;        /* create a global symbol at data start; used by startup code in order to initialise the .data section in RAM */
+        _ram_start = .;    /* create a global symbol at ram start for garbage collector */
+        . = ALIGN(4);
+        *(.data)           /* .data sections */
+        *(.data*)          /* .data* sections */
+        *(.sdata)           /* .sdata sections */
+        *(.sdata*)          /* .sdata* sections */
+        . = ALIGN(4);
+        _edata = .;        /* define a global symbol at data end; used by startup code in order to initialise the .data section in RAM */
+    } >RAM
+
+    /* Uninitialized data section */
+    .bss :
+    {
+        . = ALIGN(4);
+        _sbss = .;         /* define a global symbol at bss start; used by startup code */
+        *(.bss)
+        *(.bss*)
+        *(.sbss)
+        *(.sbss*)
+        *(COMMON)
+
+        . = ALIGN(4);
+        _ebss = .;         /* define a global symbol at bss end; used by startup code */
+    } >RAM
+
+    /* this is to define the start of the heap, and make sure we have a minimum size */
+    .heap :
+    {
+        . = ALIGN(4);
+        _heap_start = .;    /* define a global symbol at heap start */
+    } >RAM
+}

firmware/hello_world_c/uart.h

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+#ifndef UART_H_
+#define UART_H_
+
+#include <stdint.h>
+
+typedef
+__attribute__((packed))
+struct {
+    uint32_t RXTX;
+    uint32_t TXFULL;
+    uint32_t RXEMPTY;
+    uint32_t EV_STATUS;
+    uint32_t EV_PENDING;
+    uint32_t EV_ENABLE;
+    uint32_t TXEMPTY;
+    uint32_t RXFULL;
+} LiteUART;
+
+#define UART0  ((LiteUART*)0xF0003000)
+
+#endif