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zero_gravi |
<<<
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== Programming an External SPI Flash via the Bootloader
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The default processor-internal NEORV32 bootloader supports automatic booting from an external SPI flash.
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This guide shows how to write an executable to the SPI flash via the bootloader so it can be automatically
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fetched and executed after processor reset. For example, you can use a section of the FPGA bitstream configuration
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memory to store an application executable.
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[NOTE]
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This section assumes the _default_ configuration of the NEORV32 bootloader.
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See section <<_customizing_the_internal_bootloader>> on how to customize the bootloader and its setting
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(for example the SPI chip-select port, the SPI clock speed or the flash base address for storing the executable).
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:sectnums:
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=== SPI Flash
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The bootloader can access an SPI compatible flash via the processor top entity's SPI port. By default, the flash
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chip-select line is to `spi_csn_o(0)` and uses 1/8 of the processor's main clock as clock frequency.
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The SPI flash has to support single-byte read and write, 24-bit addresses and at least the following standard commands:
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* READ `0x03`
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* READ STATUS `0x05`
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* WRITE ENABLE `0x06`
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* PAGE PROGRAM `0x02`
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* SECTOR ERASE `0xD8`
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* READ ID `0x9E`
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Compatible (FGPA configuration) SPI flash memories are for example the "Winbond W25Q64FV2 or the "Micron N25Q032A".
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:sectnums:
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=== Programming an Executable
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[start=1]
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. At first, reset the NEORV32 processor and wait until the bootloader start screen appears in your terminal program.
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. Abort the auto boot sequence and start the user console by pressing any key.
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. Press u to upload the executable that you want to store to the external flash:
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[source]
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----
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CMD:> u
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Awaiting neorv32_exe.bin...
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----
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[start=4]
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. Send the binary in raw binary via your terminal program. When the upload is completed and "OK"
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appears, press `p` to trigger the programming of the flash (do not execute the image via the `e`
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command as this might corrupt the image):
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[source]
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----
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CMD:> u
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Awaiting neorv32_exe.bin... OK
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CMD:> p
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Write 0x000013FC bytes to SPI flash @ 0x00800000? (y/n)
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----
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[start=5]
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. The bootloader shows the size of the executable and the base address inside the SPI flash where the
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executable is going to be stored. A prompt appears: Type `y` to start the programming or type `n` to
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abort.
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[TIP]
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Section <<_customizing_the_internal_bootloader>> show the according C-language `define` that can be modified
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to specify the base address of the executable inside the SPI flash.
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[source]
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----
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CMD:> u
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Awaiting neorv32_exe.bin... OK
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CMD:> p
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Write 0x000013FC bytes to SPI flash @ 0x08000000? (y/n) y
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Flashing... OK
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CMD:>
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----
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[NOTE]
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The bootloader stores the executable in **little-endian** byte-order to the flash.
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[start=6]
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. If "OK" appears in the terminal line, the programming process was successful. Now you can use the
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auto boot sequence to automatically boot your application from the flash at system start-up without
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any user interaction.
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