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The i.MX RT1176 pairs the Cortex-M7 with a Cortex-M4 that NuttX left in ROM-held reset. This backend lets NuttX on the CM7 run the CM4 as an RPTUN remote. The loader writes the CM4 ELF through the LMEM backdoor window, the boot vector goes into IOMUXC_LPSR_GPR0/1 as the backdoor alias of the code TCM (the CM4-native address does not boot, which NXP's MCMGR also assumes), and SRC releases the core. A released slice cannot be held in reset again: a software reset is a pulse after which the core restarts from the boot vector. Stop therefore parks the core in a wfi loop written over the start of its image, and the next start reloads the image. Virtqueue kicks travel on MU-A channel 0. A kick into a full mailbox is coalesced, because the remote rescans every virtqueue on any kick. SRC_SRMR is set so a CM4 lockup resets only the CM4 instead of the whole chip. The board supplies the remote name, the ELF path, the address environment, the boot vector and the autostart choice through imxrt_rptun_init(). Gated by IMXRT_HAVE_CM4, which only the MIMXRT1176 selects; selects DEV_SIMPLE_ADDRENV for libmetal. Assisted-by: Claude:claude-fable-5-1 Signed-off-by: Lourens Naude <lourens@bearmetal.eu> |
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