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Initial Setup & Overlays

uEnv.txt Configuration

The following overlays must be active in your /boot/uEnv.txt:

enable_uboot_overlays=1

# UART4 for GPS NMEA
uboot_overlay_addr4=/lib/firmware/BB-UART4-00A0.dtbo

# PRU remoteproc with vring (rpmsg) support
uboot_overlay_addr5=/lib/firmware/PRU-RPROC-VRING-00A0.dtbo

# DS3231 RTC on I2C2
uboot_overlay_addr6=/lib/firmware/BB-I2C2-DS3231-00A0.dtbo

# PRU PPS pinmux (configures P8_16 as PRU input)
uboot_overlay_addr7=/lib/firmware/PRU-PPS-PINMUX-00A0.dtbo

# PRU remoteproc driver (4.19-ti style, works on 6.6-ti)
uboot_overlay_pru=AM335X-PRU-RPROC-4-19-TI-00A0.dtbo

# Disable unused overlays to reduce noise
disable_uboot_overlay_video=1
disable_uboot_overlay_audio=1

# RT/timing-optimized cmdline
cmdline=fsck.repair=yes earlycon coherent_pool=1M net.ifnames=0 lpj=1990656 \
  rng_core.default_quality=100 intel_idle.max_cstate=0 processor.max_cstate=1 idle=poll

Device Tree Overlays

PRU-PPS-PINMUX-00A0.dts

Configures P8_16 (offset 0x38) as a PRU input with pull-down disabled, input enabled, mode 6 (pr1_pru0_pru_r31_14).

Compile and install:

dtc -O dtb -o /lib/firmware/PRU-PPS-PINMUX-00A0.dtbo -b 0 -@ overlays/PRU-PPS-PINMUX-00A0.dts

PRU-RPROC-VRING-00A0.dts

This overlay wires the PRU0/PRU1 interrupt lines for rpmsg/vring communication:

  • PRU0: vring (sysevt 16, ch 2, host 2), kick (sysevt 17, ch 0, host 0)
  • PRU1: vring (sysevt 18, ch 3, host 3), kick (sysevt 19, ch 1, host 1)

Compile and install:

dtc -O dtb -o /lib/firmware/PRU-RPROC-VRING-00A0.dtbo -b 0 -@ overlays/PRU-RPROC-VRING-00A0.dts

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