BeagleBone PRU Notes
The goal of this page is to record information that is pertinent to getting started with the BeagleBone's AM335x Programmable Real-time Unit (PRU).
BeagleBone Programmable Real-time Unit
This is also called the PRU Subsystem (PRUSS) or PRU and Industrial Controller Subsystem (PRU-ICSS). It is optimized to perform embedded tasks that require real-time constraints.
Most important is the purssdrv library to expose functions to the PRU. You can load this library by typing modprobe uio_pruss.
- The PRU has dual 32-bit RISC cores, shared data and instruction memories and an interrupt controller (INTC).
- 8KB data memory and 8KB instruction memory
- 12KB shared RAM
- A small, deterministic instruction set
There is no pipelining done on the processor and there are 29 (r1-r30) registers to use.
Data Sheet is located at http://www.ti.com/lit/pdf/spruh73
BeagleBoard/TI has provided example C programs that utilize the PRU on github.
These include: PRU_memAccess_DDR_PRUsharedRAM, PRU_memAccessPRUDataRam, PRU_PRUtoPRUInterrupt, and a PRU assembler.
Full assembly guide is located at http://processors.wiki.ti.com/index.php/PRU_Assembly_Reference_Guide
Nearly all instructions (with exception of accessing memory external to PRU) are single-cycle execute (5 ns when running at 200 MHz)
Four instruction classes
- Flow Control
- Register Load/Store
- Mnemonic, followed by comma separated parameter list
- Parameters can be a register, label, immediate value, or constant table entry
- SUB r3, r3, 10
- Subtracts immediate value 10 (decimal) from the value in r3 and then places the result in r3