How to generate multiboot bitstreams by hand

You have a design other than the fpgas.online Acorn design and want its golden and operational flavours for an Acorn’s flash. The fpgas.online Acorn design’s own build produces both flavours, so this page is not needed for it. It does not cover writing the images, which is How to install the fpgas.online images on an Acorn.

This procedure is waiting for its run: test-designs issue #226.

What you need

  • Vivado, with the design open as current_design.

  • Vivado for the golden image: openXC7 does not support NEXT_CONFIG_ADDR.

Steps

  1. In Vivado, build the operational image, which has the watchdog and the fallback.

# Operational: watchdog and fallback
set_property BITSTREAM.CONFIG.TIMER_CFG 0x0001fbd0 [current_design]
set_property BITSTREAM.CONFIG.CONFIGFALLBACK Enable [current_design]
write_bitstream -force operational.bit
write_cfgmem -force -format bin -interface spix4 -size 16 -loadbit "up 0x0 operational.bit" -file operational.bin

  1. In the same Vivado session, build the golden image, which chain-loads the operational slot. It keeps step 1’s watchdog, as the golden image of the fpgas.online design does.

# Golden: chain-load the operational slot
set_property BITSTREAM.CONFIG.NEXT_CONFIG_ADDR 0x00400000 [current_design]
write_bitstream -force golden.bit
write_cfgmem -force -format bin -interface spix4 -size 16 -loadbit "up 0x0 golden.bit" -file golden.bin

The order matters: a property set stays set for the rest of the session. Built after the golden, the operational image would chain-load too. LiteX’s sqrl_acorn.py builds them in this order.

Check

The working directory holds golden.bit, golden.bin, operational.bit and operational.bin. The two .bin files are what goes into the flash. fpgas-acorn-flash write checks each against its slot before it erases anything.

If it fails

  • fpgas-acorn-flash refuses operational.bin: “this image chain-loads another one (the golden flavour): not for the operational slot”. It was built after the golden image in the same session. Build both again, in the order of the steps.

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