100. Change CAN Bus Clock to PLLAON

Background

If you would like to tweak your CAN bus to 500kbps or 1Mbps, you need to change the CAN bus clock.

There are a few major references for this issue:

• NVIDIA's guide [link]

• Developer's experience [link]

• elinux's guide of different types of dtb [link]

Result

With a proper configuration, you will find the following result.

root@nvidia-desktop:~# cat /sys/kernel/debug/bpmp/debug/clk/can1/parent
pll_aon

root@nvidia-desktop:~# ip -d -s link show can0
8: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 72 qdisc pfifo_fast state UP mode DEFAULT group default qlen 10
    link/can  promiscuity 0
    can <BERR-REPORTING,FD> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0
	  bitrate 500000 sample-point 0.870
	  tq 20 prop-seg 43 phase-seg1 43 phase-seg2 13 sjw 1
	  mttcan: tseg1 2..255 tseg2 0..127 sjw 1..127 brp 1..511 brp-inc 1
	  dbitrate 2000000 dsample-point 0.720
	  dtq 20 dprop-seg 8 dphase-seg1 9 dphase-seg2 7 dsjw 1
	  mttcan: dtseg1 1..31 dtseg2 0..15 dsjw 1..15 dbrp 1..15 dbrp-inc 1
	  clock 50000000
	  re-started bus-errors arbit-lost error-warn error-pass bus-off
	  0          0          0          0          0          0         numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535
    RX: bytes  packets  errors  dropped overrun mcast
    0          0        0       0       0       0
    TX: bytes  packets  errors  dropped carrier collsns
    0          0        0       0       0       0

Process

Basically, there are two files needed to be:

• BPMPFW DTB

  • Jetson AGX Xavier 32GB: $L4T/bootloader/t186ref/tegra194-a02-bpmp-p2888-a04.dtb

  • Jetson AGX Xavier 64GB: $L4T/bootloader/t186ref/tegra194-a02-bpmp-p2888-0005-a04.dtb

• Kernel DTB - $L4T/NRU_JetPack4.6_v1.1.dtb

We have put an example version for NRU-120S on NRU FTP.

Updating BPMPFW DTB (JAX32)

sudo -s

# Make BPMPFW DTB editable
cd $L4T/bootloader/t186ref

# Make a backup
cp tegra194-a02-bpmp-p2888-a04.dtb tegra194-a02-bpmp-p2888-a04.dtb.bak

# Convert .dtb to editable .dts
dtc -I dtb -O dts tegra194-a02-bpmp-p2888-a04.dtb -o tegra194-a02-bpmp-p2888-a04.dts

# Edit the .dts file then add "pllaon (0x5e)" as allowed-parents

...
clock@can1 {
	allow_fractional_divider = <0x1>;
	allowed-parents = <0x121 0x5b 0x13a 0x5e>; // changed
	clk-id = <0x9>;
};

clock@can2 {
	allow_fractional_divider = <0x1>;
	allowed-parents = <0x121 0x5b 0x13a 0x5e>; // changed
	clk-id = <0xb>;
};
...

# Convert .dts to flashable .dtb
dtc -I dts -O dtb tegra194-a02-bpmp-p2888-a04.dts -o tegra194-a02-bpmp-p2888-a04.dtb


# Only update BPMPFW. remember to put NRU into recovery mode
cd $L4T/
time sudo ./flash.sh -k bpmp-fw-dtb jetson-xavier mmcblk0p1

Updating BPMPFW DTB (JAX64)

sudo -s

# Make BPMPFW DTB editable
cd $L4T/bootloader/t186ref

# Make a backup
cp tegra194-a02-bpmp-p2888-0005-a04.dtb tegra194-a02-bpmp-p2888-0005-a04.dtb.bak

# Convert .dtb to editable .dts
dtc -I dtb -O dts tegra194-a02-bpmp-p2888-0005-a04.dtb -o tegra194-a02-bpmp-p2888-0005-a04.dts

# Edit the .dts file then add "pllaon (0x5e)" as allowed-parents

...
clock@can1 {
	allow_fractional_divider = <0x1>;
	allowed-parents = <0x121 0x5b 0x13a 0x5e>; // changed
	clk-id = <0x9>;
};

clock@can2 {
	allow_fractional_divider = <0x1>;
	allowed-parents = <0x121 0x5b 0x13a 0x5e>; // changed
	clk-id = <0xb>;
};
...

# Convert .dts to flashable .dtb
dtc -I dts -O dtb tegra194-a02-bpmp-p2888-0005-a04.dts -o tegra194-a02-bpmp-p2888-0005-a04.dtb


# Only update BPMPFW. remember to put NRU into recovery mode
cd $L4T/
time sudo ./flash.sh -k bpmp-fw-dtb jetson-xavier mmcblk0p1

---

Updating Kernel DTB

sudo -s

cd $L4T

# Make a backup
cp NRU_JetPack4.6_v1.1.dtb NRU_JetPack4.6_v1.1.dtb.bak

# Make dtb to editable dts
dtc -I dtb -O dts NRU_JetPack4.6_v1.1.dtb -o NRU_JetPack4.6_v1.1.dts

# Modify the .dts to enable pllaon clock and change the can clock to pllaon

...

mods-simple-bus {
       status = "okay"; // changed

       mods-clocks {
	  status = "okay"; // changed
       }
}

...

mttcan@c310000 {
...
	compatible = "nvidia,tegra194-mttcan";
	reg = <0x0 0xc310000 0x0 0x400 0x0 0xc311000 0x0 0x32 0x0 0xc312000 0x0 0x1000>;
	reg-names = "can-regs", "glue-regs", "msg-ram";
	interrupts = <0x0 0x28 0x4>;
	pll_source = "pllaon"; // changed
	clocks = <0x4 0x11c 0x4 0xa 0x4 0x9 0x4 0x5e>; // changed
	clock-names = "can_core", "can_host", "can", "pllaon"; // changed
	resets = <0x5 0x4>;
	reset-names = "can";
	mram-params = <0x0 0x10 0x10 0x20 0x0 0x0 0x10 0x10 0x10>;
	tx-config = <0x0 0x10 0x0 0x40>;
	rx-config = <0x40 0x40 0x40>;
	status = "okay";
...
};

mttcan@c320000 {
...
	compatible = "nvidia,tegra194-mttcan";
	reg = <0x0 0xc320000 0x0 0x400 0x0 0xc321000 0x0 0x32 0x0 0xc322000 0x0 0x1000>;
	reg-names = "can-regs", "glue-regs", "msg-ram";
	interrupts = <0x0 0x2a 0x4>;
	pll_source = "pllaon"; // changed
	clocks = <0x4 0x11d 0x4 0xc 0x4 0xb 0x4 0x5e>; // changed
	clock-names = "can_core", "can_host", "can", "pllaon"; // changed
	resets = <0x5 0x5>;
	reset-names = "can";
	mram-params = <0x0 0x10 0x10 0x20 0x0 0x0 0x10 0x10 0x10>;
	tx-config = <0x0 0x10 0x0 0x40>;
	rx-config = <0x40 0x40 0x40>;
	status = "okay";
...
};

...

clocks-init {
	compatible = "nvidia,clocks-config";
	status = "okay";
	disable {
		clocks = <0x4 0x9 0x4 0xb>; // changed
	};
};

...


# Make nru.dts to .dtb
dtc -I dts -O dtb NRU_JetPack4.6_v1.1.dts -o NRU_JetPack4.6_v1.1.dtb


# Only update device tree. remember to put NRU into recovery mode
cd $L4T/
time sudo ./flash.sh -k kernel-dtb -d NRU_JetPack4.6_v1.1.dtb jetson-xavier mmcblk0p1