Add Riscv example

resources/examples/embedded/riscv-qemu/Makefile

@@ -0,0 +1,23 @@
+SRCS_C3 := $(wildcard *.c3)
+
+default: hello.elf
+
+hello.a: $(SRCS_C3)
+	c3c --use-stdlib=no --no-entry --target elf-riscv32 static-lib $(SRCS_C3)
+
+start.o: start.s
+	riscv64-unknown-elf-as -g -march=rv32i -mabi=ilp32 -o start.o start.s
+
+hello.elf: hello.a start.o baremetal.ld
+	riscv64-unknown-elf-ld -T baremetal.ld -m elf32lriscv -o hello.elf hello.a start.o
+
+run: hello.elf
+	@echo "Ctrl-A C for QEMU console, then quit to exit"
+	qemu-system-riscv32 -nographic -serial mon:stdio -machine virt -bios hello.elf
+
+debug: hello.elf
+	@echo "Ctrl-A C for QEMU console, then quit to exit"
+	qemu-system-riscv32 -nographic -serial mon:stdio -machine virt -s -S -bios hello.elf
+
+clean:
+	rm -f *.o *.a hello.elf

resources/examples/embedded/riscv-qemu/README.md

@@ -0,0 +1,8 @@
+# Risc-V 32 Embedded Example With QEMU
+## Prereqs
+- QEMU
+- Risc-V toolchain
+- C3C
+- Make
+## Running
+`make run`

resources/examples/embedded/riscv-qemu/baremetal.ld

@@ -0,0 +1,14 @@
+EXTERN(main)
+
+SECTIONS
+{
+  . = 0x80000000;													/* QEMU default load address to run bios */
+  .text : {
+		KEEP(*(.text._start));								/* Ensure _start is placed first */
+		*(.text*);														/* Program code here */
+	}
+	. = ALIGN (CONSTANT (COMMONPAGESIZE));	/* Make sure linker does not jam data into text section, making text writable */
+  .data : { 
+		*(.data*)															/* Stack goes here */
+	}
+}

resources/examples/embedded/riscv-qemu/hello.c3

@@ -0,0 +1,10 @@
+import uart;
+
+const UART0_BASE = 0x10000000;
+
+fn void main() @export("main") {
+  Uart* uart0 = (Uart*)UART0_BASE;               // Create pointer to UART 0
+	uart0.fcr = uart::UARTFCR_FFENA;               // Enable FIFO
+  uart0.puts("Hello World!\n");                  // Write the string to the UART
+  while (1);                                     // Loop forever to prevent program from ending
+}

resources/examples/embedded/riscv-qemu/start.s

@@ -0,0 +1,17 @@
+# Simple C runtime startup bootstrap
+# Two primary functions:
+# - Stack allocation and initializing stack pointer
+# - Jumping to main
+
+.section .text._start
+.global _start
+_start:
+    la sp, __stack_top    # Load the stack pointer
+    add s0, sp, zero      # Set the frame pointer
+    jal zero, main        # Run main entry point - no argc
+loop:	j loop              # Spin forever in case main returns
+
+.section .data
+.space 1024*8             # allocate 8K of memory to serve as initial stack
+.align 16                 # Smallest stack allocation is 16 bytes, so align accordingly
+__stack_top:              # The stack grows downward according the Risc-V ABI

resources/examples/embedded/riscv-qemu/uart.c3

@@ -0,0 +1,28 @@
+module uart;
+
+const UARTFCR_FFENA = 0x01;                  // UART FIFO Control Register enable bit
+const UARTLSR_THRE = 0x20;                   // UART Line Status Register Transmit Hold Register Empty bit
+
+struct Uart {
+	char dr;                                   // UART Data Register
+	char filler1;
+	char fcr;                                  // FIFO Control Register
+	char filler2;
+	char filler3;
+	char lsr;                                  // Line Status Register
+}
+
+fn bool Uart.uart_ff_thr_empty(Uart* this) {
+	return (bool)($$volatile_load(&this.lsr) & UARTLSR_THRE);
+}
+
+fn void Uart.putc(Uart* this, char c) {
+  while (!this.uart_ff_thr_empty());         // Wait until the FIFO holding register is empty
+  $$volatile_store(&this.dr, c);             // Write character to transmit register
+}
+
+fn void Uart.puts(Uart* this, char *str) {
+  while (*str) {                             // Loop until value at string pointer is zero
+    this.putc(*str++);                       // Write the character and increment pointer
+  }
+}