Expand description
Abstractions over the Boot and Power Management Processor.
See Chapter 41 in the Tegra X1 Technical Reference Manual for details.
Description
The Tegra X1 Boot and Power Management Processor is referred to as BPMP-Lite or BPMP, as it represents a first architectural step towards a dedicated boot and power management processor.
The BPMP is an ARM7-based microcontroller used for power management and boot purposes. Outside of boot, the BPMP runs the “BPMP Firmware” (BPMP-FW), which provides various services related to runtime power management.
In cold boot, the BPMP-Lite processor runs the boot ROM code as well as a portion of the Boot Loader. As part of cold boot, the BPMP-FW is loaded into DRAM and the CPU triggers the BPMP-Lite processor to begin executing that firmware.
Delaying Execution
Through the Flow Controller, code execution on the BPMP can be halted
for a given delay in milliseconds or microseconds. Though the RTC is
more accurate, the main advantage of msleep and usleep over the
RTC is resource-efficiency. These functions are meant to reduce power
consumption while sleeping.
use libtegra::bpmp;
// Halt the BPMP for 32 milliseconds.
bpmp::msleep(32);
// Halt the BPMP for 32.000 microseconds, or 32 milliseconds.
bpmp::usleep(32_000);Manual Halting
For many hardware sequences, such as rebooting or powering off, there may be the
need for halting the BPMP manually. Said functionality is provided through the
halt function:
use libtegra::{bpmp, pmc};
use tock_registers::interfaces::*;
/// Forcefully reboots the SoC into Recovery Mode.
unsafe fn reboot_to_rcm() -> ! {
let pmc = &*pmc::REGISTERS;
// Additional resource cleanup here...
// (BPMP MMU disable, SD unmount, display finalization, ...)
// Reboot into RCM.
pmc.APBDEV_PMC_SCRATCH0_0.set(2);
pmc.APBDEV_PMC_CNTRL_0.set(pmc.APBDEV_PMC_CNTRL_0.get() | (1 << 4));
// Halt the BPMP.
loop {
bpmp::halt();
}
}
unsafe {
reboot_to_rcm();
}