booting from address 0x8000

[biosbob]

i'm trying to move the boot address into low memory (for reasons that will eventually become clear).... as a general test, i have a basic form of my bootloader that simply blinks some LEDs; it does not actually load code into RAM....

i'm able to move the bootloader down to address 0x10000; i've looked at the generated code to verify.... i'm even able to move the bootloader down to address 0x18000....

when moving the bootloader, i update the boot_rom_base_c as well as make a corresponding change in neorv32.ld

but when i tried to place the bootloader at 0x8000, my test bootloader fails.... should i be able to do this???? my IMEM (based at 0x0000) is only 8K in size....

[stnolting]

Hey @biosbob!

Interesting, this is a use case I did no see coming 😅 Anyway, I just tested a setup with the BOOTROM starting at 0x0000_8000 and it works without problems.

This is what I did:

1. Change the hardware definition of BOOTROM base address from

neorv32/rtl/core/neorv32_package.vhd

Line 96 in a5fc6ff

constant boot_rom_base_c : std_ulogic_vector(31 downto 0) := x"ffff0000"; -- bootloader base address, fixed!

to

constant boot_rom_base_c      : std_ulogic_vector(31 downto 0) := x"00008000"; -- bootloader base address, fixed!

2. Adapt the linker script's boot ROM definition from

neorv32/sw/common/neorv32.ld

Line 77 in a5fc6ff

rom (rx) : ORIGIN = DEFINED(make_bootloader) ? 0xFFFF0000 : __neorv32_rom_base, LENGTH = DEFINED(make_bootloader) ? 32K : __neorv32_rom_size

to

  rom   (rx) : ORIGIN = DEFINED(make_bootloader) ? 0x00008000 : __neorv32_rom_base, LENGTH = DEFINED(make_bootloader) ? 32K : __neorv32_rom_size

3. Recompile (and re-install) the bootloader source code:

neorv32/sw/bootloader$ make clean_all bootloader

[stnolting]

I just tested your configuration on my FPGA board relocating the default bootloader to 0x0000_8000 - and it works like a charm 😅

Maybe it is a software (compilation) issue? Did you test your setup using the default NEORV32 bootloader? How did you recompile the bootloader sources?

[biosbob]

here's the source to my bootloader.c.... note that my tests are using the BOOT_ONLY option, which causes the bootloader to output some bytes and toggle some GPIOs....

#include <stdint.h>
#include <neorv32.h>

#define XIP_PAGE_BASE_ADDR 0x40000000

enum SPI_FLASH_CMD {
    SPI_FLASH_CMD_WRITE         = 0x02, /**< Write data */
    SPI_FLASH_CMD_READ          = 0x03, /**< Read data */
    SPI_FLASH_CMD_READ_STATUS   = 0x05, /**< Get status register */
    SPI_FLASH_CMD_WRITE_ENABLE  = 0x06, /**< Allow write access */
    SPI_FLASH_CMD_READ_ID       = 0x9F,  /**< Get id */
    SPI_FLASH_CMD_RELEASE       = 0xAB,  /**< Get id */
    SPI_FLASH_CMD_SECTOR_ERASE  = 0xD8,  /**< Erase complete sector */
    SPI_FLASH_CMD_RESET         = 0xFF  /**< Device reset */
};

void execCmd(uint8_t cmd) {
    union {
        uint64_t uint64;
        uint32_t uint32[sizeof(uint64_t)/sizeof(uint32_t)];
    } data;
    data.uint32[0] = 0;
    data.uint32[1] = cmd << 24;
    neorv32_xip_spi_trans(1, &data.uint64);    
}

int main(void) {

#ifdef BOOT_ONLY

    neorv32_uart0_setup(115200, 0);
    neorv32_uart0_putc(0xb);

    neorv32_gpio_pin_set(0);
    neorv32_gpio_pin_set(1);
    neorv32_gpio_pin_set(2);
    neorv32_gpio_pin_set(4);
    neorv32_gpio_pin_set(6);
    for (int i = 0; i < 10; i++) {
        for (int j = 0; j < 100000; j++) asm("nop");
        neorv32_gpio_pin_toggle(1);
        neorv32_gpio_pin_toggle(2);
        neorv32_gpio_pin_toggle(4);
    }
    neorv32_uart0_putc(0xd);
    neorv32_gpio_pin_clr(0);

#else

    neorv32_xip_setup(CLK_PRSC_2, 0, 0, SPI_FLASH_CMD_READ);
    execCmd(SPI_FLASH_CMD_RESET);
    execCmd(SPI_FLASH_CMD_RELEASE);
    neorv32_xip_burst_mode_enable();
    neorv32_xip_start(3, XIP_PAGE_BASE_ADDR);
    uint32_t* src = (uint32_t*)(XIP_PAGE_BASE_ADDR + 0x20000);
    uint32_t* dst = (uint32_t*)0;
    for (uint32_t i = 0; i < 0x400; i++) {
        *dst++ = *src++;
    }
    neorv32_uart0_setup(115200, 0);
    neorv32_uart0_putc(0xb);
    neorv32_uart0_putc(0xb);
    uint32_t startAddr = 0x80;
    asm("jr %[v]" : : [v] "r" (startAddr));

#endif

    while (1) {}
    return 0; // bootloader should never return
}

my Makefile ultimately uses neorv32/sw/common/common.mk to compile/link this file....

[stnolting]

I tested your bootloader located at 0x0000_8000 and it works so there might be a problem with your compilation flow?!

my Makefile ultimately uses neorv32/sw/common/common.mk to compile/link this file....

What commands/targets do you use to compile and install the bootloader? Do you set any makefile flags?

[biosbob]

i think i found the problem.... the bootloader at 0x8000 WORKS on my cmod board, but *FAILS on my icebreaker board....

since vivado takes so long to build, i had plenty of time to review osflow/devices/ice40/neorv32_imem.ice40up_spram.vhd, which contains what i think is the issue:

  -- IO space: module base address --
  constant hi_abb_c : natural := 31; -- high address boundary bit
  constant lo_abb_c : natural := index_size_f(64*1024); -- low address boundary bit

correct me if i'm wrong, but this module assumes it controls an entire 64K address space -- into which i have inserted the bootloader into its upper 32K!!!!

somehow the IMEM_SIZE (and DMEM_SIZE) generics should ultimately determine the low-address boundary bit.... adding generics to this module might be the way to go....

[stnolting]

I'll update the SPRAM-based IMEM/DMEM modules in stnolting/neorv32-setups#101 😉

[biosbob]

replacing the fixed 64*1024 constants in neorv32_{di}mem.ice40up_spram.vhd with {DI}MEM_SIZE does in fact work.... in my case, i'll be "compacting" my address space -- and this fix allows me to re-use these modules without internal changes....

by no means a high-priority, however....