<<< :sectnums: ==== Instruction Memory (IMEM) [cols="<3,<3,<4"] [grid="none"] |======================= | Hardware source files: | neorv32_imem.vhd | default platform-agnostic instruction memory (RAM or ROM) | | neorv32_application_image.vhd | initialization image (a VHDL package) | Software driver files: | none | _implicitly used_ | Top entity ports: | none | | Configuration generics: | `MEM_INT_IMEM_EN` | implement processor-internal IMEM when `true` | | `MEM_INT_IMEM_SIZE` | IMEM size in bytes (use a power of 2) | | `BOOT_MODE_SELECT` | implement IMEM as ROM when `BOOT_MODE_SELECT` = 2; see <<_boot_configuration>> | CPU interrupts: | none | |======================= **Overview** Implementation of the processor-internal instruction memory is enabled by the processor's `MEM_INT_IMEM_EN` generic. The total memory size in bytes is defined via the `MEM_INT_IMEM_SIZE` generic. Note that this size should be a power of two to optimize physical implementation. If enabled, the IMEM is mapped to base address `0x00000000` (see section <<_address_space>>). By default the IMEM is implemented as true RAM so the content can be modified during run time. This is required when using the <<_bootloader>> (or the <<_on_chip_debugger_ocd>>) so it can update the content of the IMEM at any time. Alternatively, the IMEM can be implemented as **pre-initialized read-only memory (ROM)**, so the processor can directly boot from it after reset. This option is configured via the `BOOT_MODE_SELECT` generic. See section <<_boot_configuration>> for more information. The initialization image is embedded into the bitstream during synthesis. The software framework provides an option to generate and override the default VHDL initialization file `rtl/core/neorv32_application_image.vhd`, which is automatically inserted into the IMEM (see <<_makefile_targets>>. If the IMEM is implemented as RAM (default), the memory block will not be initialized at all. .Platform-Specific Memory Primitives [NOTE] If required, the default IMEM can be replaced by a platform-/technology-specific primitive to optimize area utilization, timing and power consumption. .Memory Size [NOTE] If the configured memory size (via the `MEM_INT_IMEM_SIZE` generic) is not a power of two the actual memory size will be auto-adjusted to the next power of two (e.g. configuring a memory size of 60kB will result in a physical memory size of 64kB). .Legacy HDL Style [TIP] If synthesis fails to infer block RAM for the IMEM, turn on the `alt_style_c` option inside the memory's VHDL source file. When enabled, a different HDL style is used to describe the memory core. .Read-Only Access [NOTE] If the IMEM is implemented as ROM any write attempt to it will raise a _store access fault_ exception.