5.4.2.2. Modifying Linker Memory Regions

Nios® II Software Developer Handbook

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Date 8/28/2023

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5.4.2.2. Modifying Linker Memory Regions

If the linker memory regions that are created by default do not meet your needs, BSP Tcl commands let you modify the memory regions as desired.

Suppose you have a memory region named onchip_ram. The Tcl script named reserve_1024_onchip_ram.tcl separates the top 1024 bytes of onchip_ram to create a new region named onchip_special.

For more information about an explanation of each Tcl command used in this example, refer to the " Nios® II Software Build Tools Reference" chapter.

# Get region information for onchip_ram memory region. 
# Returned as a list. 
set region_info [get_memory_region onchip_ram] 
# Extract fields from region information list. 
set region_name [lindex $region_info 0] 
set slave_desc [lindex $region_info 1] 
set offset [lindex $region_info 2] 
set span [lindex $region_info 3] 
# Remove the existing memory region. 
delete_memory_region $region_name 
# Compute memory ranges for replacement regions. 
set split_span 1024 
set new_span [expr $span-$split_span] 
set split_offset [expr $offset+$new_span] 
# Create two memory regions out of the original region. 
add_memory_region onchip_ram $slave_desc $offset $new_span 
add_memory_region onchip_special $slave_desc $split_offset $split_span

If you pass this Tcl script to nios2-bsp, it runs after the default Tcl script runs and sets up a linker region named onchip_ram0. You pass the Tcl script to nios2-bsp as follows:

nios2-bsp hal my_bsp --script reserve_1024_onchip_ram.tcl

Note: Take care that one of the new memory regions has the same name as the original memory region.

If you run nios2-bsp again to update your BSP without providing the --script option, your BSP reverts to the default linker memory regions and your onchip_special memory region disappears. To preserve it, you can either provide the --script option to your Tcl script or pass the DONT_CHANGE keyword to the default Tcl script as follows:

nios2-bsp hal my_bsp --default_memory_regions DONT_CHANGE

Intel FPGA recommends that you use the --script approach when updating your BSP. This approach allows the default Tcl script to update memory regions if memories are added, removed, renamed, or resized. Using the DONT_CHANGE keyword approach does not handle any of these cases because the default Tcl script does not update the memory regions at all.

For more information about using the --script argument, refer to the “Calling a Custom BSP Tcl Script” section.

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5.4.2.2. Modifying Linker Memory Regions