reset synchronizer

10 files changed, 152 insertions, 137 deletions

diff --git a/Makefile b/Makefile
index b364bde..e5a37b7 100644
--- a/Makefile
+++ b/Makefile
@@ -45,6 +45,7 @@ RISCV_AS = $(RISCV_TOOLCHAIN)-as
 RISCV_CC = $(RISCV_TOOLCHAIN)-gcc
 RISCV_LD = $(RISCV_TOOLCHAIN)-ld
 RISCV_OBJCOPY = $(RISCV_TOOLCHAIN)-objcopy
+RISCV_OBJDUMP = $(RISCV_TOOLCHAIN)-objdump
 
 RISCV_ASFLAGS = -march=rv32i -mabi=ilp32
 RISCV_CFLAGS = -march=rv32i -mabi=ilp32
@@ -159,9 +160,12 @@ $(BUILD_DIR):
 wave:
 	$(GTKWAVE) -a debug/cpu.gtkw $(BUILD_DIR)/waveform_cpu.vcd
 
+objdump: $(PROG_ELF_FILE)
+	$(RISCV_OBJDUMP) -d -x --disassembler-color=on $(PROG_ELF_FILE)
+
 # Clean
 clean:
 	rm -rf $(BUILD_DIR)
 
-.PHONY: all simulate rom bitsream upload flash wave clean
+.PHONY: all simulate rom bitsream upload flash wave objdump clean
 
diff --git a/include/consts.vh b/include/consts.vh
index be1c647..e0f6e5f 100644
--- a/include/consts.vh
+++ b/include/consts.vh
@@ -126,14 +126,4 @@ parameter ROM_END   = 32'h000F_FFFF;
 parameter RAM_BEGIN = 32'h0010_0000;
 parameter RAM_END   = 32'hFF0F_FFFF;
 
-// 0000 0000 Reserved
-// 0000 FFFF
-//
-// 0001 0000 ROM
-// 000F FFFF
-//
-// 0010 0000 RAM
-// FF0F FFFF
-//
-// FF10 0000 Reserved
-// FFFF FFFF
+parameter PC_INITIAL = 32'h0001_0000;
diff --git a/prog/link.ld b/prog/link.ld
index 9644d59..ae0988f 100644
--- a/prog/link.ld
+++ b/prog/link.ld
@@ -1,67 +1,79 @@
-/* Linker script for RISC-V */
-
-/* Define memory regions */
 MEMORY
 {
-    ROM (rx)  : ORIGIN = 0x00010000, LENGTH = 0x1000  /* 1024 bytes for ROM */
-    RAM (rwx) : ORIGIN = 0x00100000, LENGTH = 0x1000  /* 1024 bytes for RAM */
+  ROM (rx)  : ORIGIN = 0x00010000, LENGTH = 4K
+  RAM (rwx) : ORIGIN = 0x00100000, LENGTH = 4K
 }
 
 ENTRY(_start)
 
-/* Define sections */
 SECTIONS
 {
-    /* Code section */
-    .text :
-    {
-        KEEP(*(.init))
-        KEEP(*(.text))
-        KEEP(*(.fini))
-        KEEP(*(.rodata))
-        _etext = .;
-    } > ROM
+  .text :
+  {
+    _stext = .;
+    . = ORIGIN(ROM);
+    _start = .;       /* Entry point address */
+    KEEP(*(.text.startup)) /* Ensure startup code is kept */
+    *(.text)          /* .text sections (code) */
+    *(.text.*)
+    . = ALIGN(4);
+    _etext = .;       /* End of code section, needed for copying .data */
+  } > ROM
 
-    /* Initialized data section */
-    .data : AT(_etext)
-    {
-        _sdata = .;
-        KEEP(*(.data))
-        _edata = .;
-    } > RAM
+  .rodata :
+  {
+    *(.rodata)               /* Read-only data */
+    *(.rodata.*)
+  } > ROM
 
-    /* Uninitialized data section */
-    .bss :
-    {
-        _sbss = .;
-        KEEP(*(.bss))
-        KEEP(*(COMMON))
-        _ebss = .;
-    } > RAM
+  .data : 
+  {
+    _sidata = LOADADDR(.data); /* Start address of .data section in ROM */
+    . = ALIGN(4);
+    _sdata = .;       /* Start of .data section in RAM */
+    *(.data)          /* .data sections (initialized data) */
+    *(.data.*)
+    *(.sdata)                  /* .sdata sections (small initialized data) */
+    *(.sdata.*)
+    . = ALIGN(4);
+    _edata = .;       /* End of .data section in RAM */
+  } > RAM AT > ROM
 
-    /* Stack section */
-    .stack (NOLOAD) :
-    {
-        _stack_start = .;
-        . += 0x100; /* Adjust the size as needed */
-        _stack_end = .;
-    } > RAM
+  .bss :
+  {
+    . = ALIGN(4);
+    _sbss = .;        /* Start of .bss section */
+    *(.bss)           /* .bss sections (zero-initialized data) */
+    *(.bss.*)
+    *(.sbss)                   /* .sbss sections (small zero-initialized data) */
+    *(.sbss.*)
+    *(COMMON)
+    . = ALIGN(4);
+    _ebss = .;        /* End of .bss section */
+  } > RAM
 
-    /* Heap section */
-    .heap (NOLOAD) :
-    {
-        _heap_start = .;
-        . += 0x100; /* Adjust the size as needed */
-        _heap_end = .;
-    } > RAM
-}
+  .heap (NOLOAD) :
+  {
+    . = ALIGN(4);
+    _sheap = .;       /* Start of heap */
+    . = . + 1K;       /* Size of heap (adjust as needed) */
+    _eheap = .;       /* End of heap */
+    . = ALIGN(4);
+  } > RAM
 
-/* Define symbols for memory initialization */
-PROVIDE(_start = 0x00010000);
-PROVIDE(_etext = _etext);
-PROVIDE(_sdata = _sdata);
-PROVIDE(_edata = _edata);
-PROVIDE(_sbss = _sbss);
-PROVIDE(_ebss = _ebss);
-PROVIDE(_sstack = _sstack);
-PROVIDE(_estack = _estack);
\ No newline at end of file
+  .stack (NOLOAD) :
+  {
+    . = ALIGN(4);
+    _sstack = .;      /* Start of stack */
+    . = . + 1K;       /* Size of stack (adjust as needed) */
+    _estack = .;      /* End of stack */
+    . = ALIGN(4);
+  } > RAM
+
+  /DISCARD/ : 
+  {
+    *(.comment)
+    *(.note)
+    *(.note.*)
+  }
+}
diff --git a/prog/src/main.c b/prog/src/main.c
index 082172d..a31196f 100644
--- a/prog/src/main.c
+++ b/prog/src/main.c
@@ -1,13 +1,12 @@
 #include <stdint.h>
 
-//volatile uint32_t *io_in  = (volatile uint32_t *)0x00000000;
-//volatile uint32_t *io_out = (volatile uint32_t *)0x00000004; 
+volatile uint32_t *io_in  = (volatile uint32_t *)0x00000000;
+volatile uint32_t *io_out = (volatile uint32_t *)0x00000004;
+
 
 int main(void) {
   while (1) {
-    for (int i = 0; i < 32; ++i) {
-      *((volatile uint32_t *)0x00000004) = i;
-      for (int j = 0; j < 1024 * 128; ++j);
-    }
+    if (*io_in) *io_out = 0b00000;
+    else *io_out = 0b11111;
   }
 }
diff --git a/prog/src/prog.s b/prog/src/prog.s.tst
index ec227a9..ec227a9 100644
--- a/prog/src/prog.s
+++ b/prog/src/prog.s.tst
diff --git a/prog/src/startup.c b/prog/src/startup.c
new file mode 100644
index 0000000..32aa131
--- /dev/null
+++ b/prog/src/startup.c
@@ -0,0 +1,39 @@
+extern unsigned int _sidata; /* Start address for the .data section in ROM */
+extern unsigned int _sdata;  /* Start address for the .data section in RAM */
+extern unsigned int _edata;  /* End address for the .data section in RAM */
+extern unsigned int _sbss;   /* Start address for the .bss section */
+extern unsigned int _ebss;   /* End address for the .bss section */
+extern unsigned int _estack; /* End address for the stack section */
+
+void main(void);             /* The main function declaration */
+void _start(void) __attribute__((section(".text.startup"), naked)); /* The entry point */
+
+void _start(void)
+{
+    unsigned int *src, *dest;
+
+    /* Copy .data section from ROM to RAM */
+    src = &_sidata;  /* ROM address of the .data section */
+    for (dest = &_sdata; dest < &_edata;)
+    {
+        *dest++ = *src++;
+    }
+
+    //while(1);
+
+    /* Zero initialize .bss section */
+    for (dest = &_sbss; dest < &_ebss;)
+    {
+        *dest++ = 0;
+    }
+
+
+    /* Initialize stack pointer */
+    asm volatile ("la sp, _estack");
+
+    /* Call the main function */
+    main();
+
+    /* If main returns, loop forever */
+    while (1);
+}
diff --git a/prog/src/startup.s b/prog/src/startup.s
deleted file mode 100644
index 963c288..0000000
--- a/prog/src/startup.s
+++ /dev/null
@@ -1,59 +0,0 @@
-.section .init
-.globl _start
-_start:
-
-prog:
-/*
-    la t0, 4
-    la t1, 1
-
-    sw t1, 0(t0)
-
-    la t0, 0x00100000
-    li t1, 1
-    sw t1, 0(t0)
-    lw t2, 0(t0)
-
-    
-    j halt
-
-*/
-    /* Set up stack pointer */
-    la sp, _stack_end
-
-    /* Initialize .data section (copy from LMA to VMA) */
-    la t0, _sdata       /* VMA start of .data */
-    la t1, _edata       /* VMA end of .data */
-    la t2, _etext       /* LMA start of .data in flash */
-copy_data:
-    beq t0, t1, clear_bss
-    lw t3, 0(t2)
-    sw t3, 0(t0)
-    addi t0, t0, 4
-    addi t2, t2, 4
-    j copy_data
-
-clear_bss:
-    /* Clear .bss section */
-    la t0, _sbss        /* VMA start of .bss */
-    la t1, _ebss        /* VMA end of .bss */
-clear_loop:
-    beq t0, t1, init_libc
-    sw x0, 0(t0)
-    addi t0, t0, 4
-    j clear_loop
-
-init_libc:
-    /* Call libc initialization functions */
-    /* call _init */
-
-    /* Call main function */
-    call main
-
-finalize_libc:
-    /* Call libc finalization functions */
-    /* call _fini */
-
-halt:
-    /* Infinite loop after main returns */
-    j halt
diff --git a/src/pc_reg.v b/src/pc_reg.v
index 2bdb540..11fe9ba 100644
--- a/src/pc_reg.v
+++ b/src/pc_reg.v
@@ -8,7 +8,7 @@ module pc_reg (
   output reg [31:0] pc
 );
 
-parameter PC_INITIAL = 32'h0001_0000;
+`include "include/consts.vh"
 
 always @ (posedge clk or negedge rstn) begin
   if (!rstn) pc <= PC_INITIAL;
diff --git a/src/reset_synchronizer.v b/src/reset_synchronizer.v
new file mode 100644
index 0000000..b957a4b
--- /dev/null
+++ b/src/reset_synchronizer.v
@@ -0,0 +1,22 @@
+module reset_synchronizer (
+    input clk,
+    input rstn_async,
+    output rstn
+);
+
+reg rstn_meta;
+reg rstn_sync_reg;
+
+always @(posedge clk or negedge rstn_async) begin
+  if (!rstn_async) begin
+    rstn_meta <= 1'b0;
+    rstn_sync_reg <= 1'b0;
+  end else begin
+    rstn_meta <= 1'b1;
+    rstn_sync_reg <= rstn_meta;
+  end
+end
+
+assign rstn = rstn_sync_reg;
+
+endmodule
\ No newline at end of file
diff --git a/src/top.v b/src/top.v
index fc1d9fe..b10fbca 100644
--- a/src/top.v
+++ b/src/top.v
@@ -1,23 +1,31 @@
 module top (
 	input clk,
 	input key,
+  input rst,
   output [5:0] led
 );
 
-wire rstn, clk_cpu;
-assign rstn = key;
+wire rstn, rstn_async, clk_cpu;
+assign rstn_async = rst;
 
 wire [31:0] io_in;
 wire [31:0] io_out;
 
+reset_synchronizer reset_synchronizer (
+  .clk(clk),
+  .rstn_async(rstn_async),
+  .rstn(rstn)
+);
+
 clock_divider #(.N(1)) clkdiv (
-    .clk(clk),
-    .rstn(rstn),
-    .clk_div(clk_cpu)
+  .clk(clk),
+  .rstn(rstn),
+  .clk_div(clk_cpu)
 );
 
 assign led[0] = ~clk_cpu;
 assign led[5:1] = ~io_out[4:0];
+assign io_in[0] = key;
 
 
 cpu cpu (