copy

firmware/Makefile

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+TARGET      = firmware
+BAUDRATE    = 115200
+SERIALPORT ?= /dev/ttyACM0
+
+CROSS  ?= riscv64-unknown-elf-
+
+CC      = $(CROSS)gcc
+OBJCOPY = $(CROSS)objcopy
+
+CFLAGS  = -march=rv32i -mabi=ilp32 -g -Os -Wall -Werror
+LDFLAGS = -Tsoc.ld -Triscv_standalone.ld  -nostdlib
+
+SOURCES = \
+	start.S \
+	$(TARGET).c
+
+
+# By default, build our binary.
+all: $(TARGET).bin
+
+#
+# Firmware binary.
+#
+
+$(TARGET).elf: $(SOURCES) soc.ld resources.h
+	$(CC) $(CFLAGS) $(LDFLAGS) $(SOURCES) -o $@
+
+$(TARGET).bin: $(TARGET).elf
+	$(OBJCOPY) -O binary $< $@
+
+
+#
+# Virtual/command targets.
+#
+
+.PHONY: clean
+
+clean:
+	rm -f $(TARGET).elf $(TARGET).bin

firmware/firmware.c

@@ -0,0 +1,71 @@
+/**
+ * Copyright (c) 2020 Great Scott Gadgets <info@greatscottgadgets.com>
+ * Copyright (c) 2022 Hans Baier <hansfbaier@gmail.com>
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+
+#include <stdbool.h>
+#include <stdint.h>
+#include "resources.h"
+
+#define ARRAY_SIZE(array) (sizeof(array) / sizeof(*array))
+
+//
+// Support functions.
+//
+
+/**
+ * Transmits a single charater over our example UART.
+ */
+void print_char(char c)
+{
+	while(!uart_tx_rdy_read());
+	uart_tx_data_write(c);
+}
+
+/**
+ * Transmits a string over our UART.
+ */
+void uart_puts(char *str)
+{
+	for (char *c = str; *c; ++c) {
+		if (*c == '\n') {
+			print_char('\r');
+		}
+
+		print_char(*c);
+	}
+}
+
+/**
+ * Prints a hex character over our UART.
+ */
+void print_nibble(uint8_t nibble)
+{
+	static const char hexits[] = "0123456789abcdef";
+	print_char(hexits[nibble & 0xf]);
+}
+
+/**
+ * Prints a single byte, in hex, over our UART.
+ */
+void print_byte(uint8_t byte)
+{
+	print_nibble(byte >> 4);
+	print_nibble(byte & 0xf);
+}
+
+//
+// Core application.
+//
+
+int main(void)
+{
+	uart_puts("SoC started! (built: " __TIME__ ")\n");
+
+	while (1) {
+		for(int i=0; i<(1<<23); i++) ;
+		uart_puts("Ping...\r\n");
+	}
+}

firmware/riscv_standalone.ld

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+OUTPUT_FORMAT("elf32-littleriscv")
+OUTPUT_ARCH("riscv")
+ENTRY(_start)
+
+SECTIONS
+{
+	. = 0x00000000;
+
+	/* Start of day code. */
+	.init :
+	{
+		*(.init) *(.init.*)
+	} > rom
+	.text :
+	{
+		*(.text) *(.text.*)
+	} > rom
+
+	.rodata :
+	{
+		*(.rodata) *(.rodata.*)
+	} > rom
+	.sdata :
+	{
+		PROVIDE(__global_pointer$ = .);
+		*(.sdata) *(.sdata.*)
+	}
+	.data :
+	{
+		*(.data) *(.data.*)
+	} > ram
+	.bss :
+	{
+		*(.bss) *(.bss.*)
+	} > ram
+
+	/DISCARD/ :
+	{
+		*(.eh_frame) *(.eh_frame.*)
+	}
+
+}
+
+PROVIDE(__stack_top = ORIGIN(ram) + LENGTH(ram));

firmware/start.S

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+/*
+ * Copyright (c) 2020 Great Scott Gadgets <info@greatscottgadgets.com>
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+.section .init, "ax"
+
+.global _start
+_start:
+    .cfi_startproc
+    .cfi_undefined ra
+
+    /* Set up our global pointer. */
+    .option push
+    .option norelax
+    la gp, __global_pointer$
+    .option pop
+
+    /* Set up our stack. */
+    la sp, __stack_top
+    add s0, sp, zero
+
+    /*
+     * NOTE: In most cases, we'd clear the BSS, here.
+     *
+     * In our case, our FPGA automaticaly starts with all of our RAM
+     * initialized to zero; so our BSS comes pre-cleared. We'll skip the
+     * formality of re-clearing it.
+     */
+
+    /* Finally, start our main routine. */
+    jal zero, main
+
+    .cfi_endproc
+    .end