This example demonstrates how to use the IPC ISR feature (which allows an IPC to run in the context of a High Priority Interrupt). The level of the IPC ISR interrupt depends on the CONFIG_ESP_SYSTEM_CHECK_INT_LEVEL option. The IPC ISR feature can be useful in cases where users need to quickly get the state of the other CPU (consult the IPC documentation). The asm_funcs.S file contains the callback that will be run on the other core. The callback should be fairly simple and must be entirely in assembly.

The first assembly callback get_ps_other_cpu() demonstrates a callback that simply returns the PS register of other core.

The second assembly callback extended_ipc_isr_asm() demonstrates a more complex callback that uses a buffer (provided as the callback's argument) to save some registers and return multiple values from the callback. The callback's void *arg points to a buffer containing the following:

uint32_t regs[]; that gives the callback an area to save some of the CPUs registers. Saving the registers gives the callback more scratch registers to use.
uint32_t in[]; that gives the callback multiple input arguments
uint32_t out[]; that gives the callback multiple output arguments

The extended_ipc_isr_asm() callback will simply save/restore registers to/from regs[], then use the arguments passed by in[] to do some work, then write the results to out[].

How to use example

Hardware Required

Example should be able to run on any commonly available ESP32 development board. The chip should have two cores.

Configure the project

CONFIG_FREERTOS_UNICORE - disabled,
CONFIG_ESP_IPC_ISR_ENABLE - enabled.

idf.py menuconfig

Build and Flash

idf.py build flash monitor

(To exit the serial monitor, type Ctrl-].)

See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.

Example output

I (304) example: Start
I (304) example: call get_ps_other_cpu
I (314) example: PS_INTLEVEL = 0x5
I (314) example: PS_EXCM = 0x0
I (324) example: PS_UM = 0x1
I (324) example: call extended_ipc_isr_asm
I (324) example: in[0] = 0x1
I (334) example: in[1] = 0x2
I (334) example: in[2] = 0x3
I (334) example: out[0] = (in[0] | in[1] | in[2]) = 0x3
I (344) example: out[1] = (in[0] + in[1] + in[2]) = 0x6
I (354) example: out[2] = in[2] = 0x3
I (354) example: out[3] = PS of other cpu = 0x25
I (364) example: End