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Jason Kridner authoredc3de7ef6
Moving to the BeagleBone AI
So far all our examples have focussed mostly on the BeagleBone Black and Pocket Beagle. These are both based on the am335x chip. The new kid on the block is the BeagleBone AI which is based on the am5729. The new chip brings with it new capabilities one of which is four PRUs. This chapter details what changes when moving from two to four PRUs.
The following are resources used in this chapter.
Moving from two to four PRUs
Problem
You have code that works on the am335x PRUs and you want to move it to the am5729 on the AI.
Solution
Things to consider when moving to the AI are:
- Which pins are you going to use
- Which PRU are you going to run on
Knowing which pins to use impacts the PRU you'll use.
Discission
The various System Reference Manuals (SRM's) list which pins go to the PRUs. Here the tables are combined into one to make it easier to see what goes where.
| PRU 0 | Bit 0 | Black pin P9_31 | AI PRU1 pin | AI PRU2 pin P8_44 | Pocket pin P1.36 |
| 0 | 1 | P9_29 | P8_41 | P1.33 | |
| 0 | 2 | P9_30 | P8_42/P8_21 | P2.32 | |
| 0 | 3 | P9_28 | P8_12 | P8_39/P8_20 | P2.30 |
| 0 | 4 | P9_92 | P8_11 | P8_40/P8_25 | P1.31 |
| 0 | 5 | P9_27 | P9_15 | P8_37/P8_24 | P2.34 |
| 0 | 6 | P9_91 | P8_38/P8_5 | P2.28 | |
| 0 | 7 | P9_25 | P8_36/P8_6 | P1.29 | |
| 0 | 8 | P8_34/P8_23 | |||
| 0 | 9 | P8_35/P8_22 | |||
| 0 | 19 | P8_33/P8_3 | |||
| 0 | 11 | P8_31/P8_4 | |||
| 0 | 12 | P8_32 | |||
| 0 | 13 | P8_45 | |||
| 0 | 14 | P8_12(out) P8_16(in)| | P9_11 | P2.24 | |
| 0 | 15 | P8_11(out) P8_15(in)| | P8_17/P9_13 | P2.33 | |
| 0 | 16 | P9_41(in) P9_26(in)| | P8_27 | ||
| 0 | 17 | P9_26 | P8_28 | ||
| 0 | 18 | P8_29 | |||
| 0 | 19 | P8_30 | |||
| 0 | 20 | P8_46/P8_8 | |||
| 1 | 0 | P8_45 | P8_32 | ||
| 1 | 1 | P8_46 | P9_20 | ||
| 1 | 2 | P8_43 | P9_19 | ||
| 1 | 3 | P8_44 | P9_41 | ||
| 1 | 4 | P8_41 | |||
| 1 | 5 | P8_42 | P8_18 | P9_25 | |
| 1 | 6 | P8_39 | P8_19 | P8_9 | |
| 1 | 7 | P8_40 | P8_13 | P9_31 | |
| 1 | 8 | P8_27 | P9_18 | P2.35 | |
| 1 | 9 | P8_29 | P8_14 | P9_17 | P2.01 |
| 1 | 10 | P8_28 | P9_42 | P9_31 | P1.35 |
| 1 | 11 | P8_30 | P9_27 | P9_29 | P1.04 |
| 1 | 12 | P8_21 | P9_30 | ||
| 1 | 13 | P8_20 | P9_26 | ||
| 1 | 14 | P9_14 | P9_42 | P1.32 | |
| 1 | 15 | P9_16 | P8_10 | P1.30 | |
| 1 | 16 | P9_26(in) | P8_15 | P8_7 | |
| 1 | 17 | P8_26 | P8_27 | ||
| 1 | 18 | P8_16 | P8_45 | ||
| 1 | 19 | P8_46 | |||
| 1 | 19 | P8_43 | |||
The pins in bold are already configured as pru pins. See :ref:`ai_config` to see what's currently configured as what. See :ref:`ai_device_tree` to configure pins.
Seeing how pins are configured
Problem
You want to know how the pins are currently configured.
Solution
The show-pins.pl command does what you want, but you have to set it up first.
bone$ cd ~/bin
bone$ ln -s /opt/scripts/device/bone/show-pins.pl .This creates a symbolic link to the show-pins.pl command that is rather hidden
away. The link is put in the bin directory which is in the default command
$PATH. Now you can run show-pins.pl from anywhere.
bone$ *show-pins.pl*
P9.19a 16 R6 7 fast rx up i2c4_scl
P9.20a 17 T9 7 fast rx up i2c4_sda
P8.35b 57 AD9 e fast down gpio3_0
P8.33b 58 AF9 e fast down gpio3_1
...Here you see P9.19a and P9.20a are configured for i2c with pull up resistors.
The P8 pins are configured as gpio with pull down resistors. They are
both on gpio port 3. P8.35b is bit 0 while P8.33b is bit 1. You can find
which direction they are set by using gpioinfo and the chip number.
Unfortunately you subtract one from the port number to get the chip number.
So P8.35b is on chip number 2.
bone$ *gpioinfo 2*
line 0: unnamed unused *input* active-high
line 1: unnamed unused *input* active-high
line 2: unnamed unused input active-high
line 3: unnamed unused input active-high
line 4: unnamed unused input active-high
...Here we see both (lines 0 and 1) are set to input.
Adding -v gives more details.
bone$ *show-pins.pl -v*
...
sysboot 14 14 H2 f fast down sysboot14
sysboot 15 15 H3 f fast down sysboot15
P9.19a 16 R6 7 fast rx up i2c4_scl
P9.20a 17 T9 7 fast rx up i2c4_sda
18 T6 f fast down Driver off
19 T7 f fast down Driver off
bluetooth in 20 P6 8 fast rx uart6_rxd mmc@480d1000 (wifibt_extra_pins_default)
bluetooth out 21 R9 8 fast rx uart6_txd mmc@480d1000 (wifibt_extra_pins_default)
...The best way to use show-pins.pl is with grep. To see all the pru pins try:
bone$ *show-pins.pl | grep -i pru | sort*
P8.13 100 D3 c fast rx pr1_pru1_gpi7
P8.15b 109 A3 d fast down pr1_pru1_gpo16
P8.16 111 B4 d fast down pr1_pru1_gpo18
P8.18 98 F5 c fast rx pr1_pru1_gpi5
P8.19 99 E6 c fast rx pr1_pru1_gpi6
P8.26 110 B3 d fast down pr1_pru1_gpo17
P9.16 108 C5 d fast down pr1_pru1_gpo15
P9.19b 95 F4 c fast rx up pr1_pru1_gpi2
P9.20b 94 D2 c fast rx up pr1_pru1_gpi1Here we have nine pins configured for the PRU registers R30 and R31.
Five are input pins and four are out.
Configuring pins on the AI via device trees
Problem
I want to configure another pin for the PRU, but I get an error.
bone$ *config-pin P9_31 pruout*
ERROR: open() for /sys/devices/platform/ocp/ocp:P9_31_pinmux/state failed, No such file or directorySolution
The pins on the AI must be configure at boot time and therefor cannot be
configured with config-pin. Instead you must edit the device tree.
Discission
Suppose you want to make P9_31 a PRU output pin. First go to the
am5729 System Reference Manual
and look up P9_31.