Multi-core

In Zephyr 3.2.0 see `zephyr/include/zephyr/drivers/ipm.h` for some starting points to understand inter-processor messaging.

• https://ostconf.com/system/attachments/files/000/001/688/original/Brodkin_Linux_Piter_presentation.pdf?1570035188

One of two or three Zephyr 3.2.0 sample apps which touch on multi-core firmware design:

• ./subsys/ipc/openamp/boards/lpcxpresso55s69_cpu0.overlay

^ Zephyr sys init run levels

Likely for another local article, excerpt from `zephyr/include/zephyr/init.h`:

 18 /*
 19  * System initialization levels. The PRE_KERNEL_1 and PRE_KERNEL_2 levels are
 20  * executed in the kernel's initialization context, which uses the interrupt
 21  * stack. The remaining levels are executed in the kernel's main task.
 22  */
 23 
 24 #define _SYS_INIT_LEVEL_PRE_KERNEL_1    0
 25 #define _SYS_INIT_LEVEL_PRE_KERNEL_2    1
 26 #define _SYS_INIT_LEVEL_POST_KERNEL     2
 27 #define _SYS_INIT_LEVEL_APPLICATION     3
 28 
 29 #ifdef CONFIG_SMP
 30 #define _SYS_INIT_LEVEL_SMP             4
 31 #endif

^ Build invocations and BOARD_ROOT setting

1361  west build -b lpcxpresso55s69_cpu0 -t menuconfig -- -DBOARD_ROOT=../..

^ General MCU bring-up

NXP LPC55S69 system clock settings HAL source file:

$ vi ./hal/nxp/mcux/mcux-sdk/devices/LPC55S69/drivers/fsl_clock.h

^ NXP mailbox HAL files

modules/hal/nxp/mcux/mcux-sdk/drivers/mailbox/fsl_mailbox.h

Size of data block which mailbox can send:

$ grep -nr MCUX_IPM_DATA_REGS ./*
./nexus-gateway-firmware/samples/ipm_mcux/build/zephyr/zephyr.lst:8385:	return MCUX_IPM_DATA_REGS*sizeof(uint32_t);
./nexus-gateway-firmware/samples/ipm_mcux/build/zephyr/zephyr.lst:8433:	if (size > MCUX_IPM_DATA_REGS * sizeof(uint32_t)) {
./nexus-gateway-firmware/samples/ipm_mcux/build/ipm_mcux_remote-prefix/src/ipm_mcux_remote-build/zephyr/zephyr.lst:6266:	return MCUX_IPM_DATA_REGS*sizeof(uint32_t);
./nexus-gateway-firmware/samples/ipm_mcux/build/ipm_mcux_remote-prefix/src/ipm_mcux_remote-build/zephyr/zephyr.lst:6314:	if (size > MCUX_IPM_DATA_REGS * sizeof(uint32_t)) {
./tags:6361980:MCUX_IPM_DATA_REGS	zephyr/drivers/ipm/ipm_mcux.c	16;"	d	file:
./zephyr/drivers/ipm/ipm_mcux.c:16:#define MCUX_IPM_DATA_REGS 1
./zephyr/drivers/ipm/ipm_mcux.c:82:	uint32_t data32[MCUX_IPM_DATA_REGS]; /* Until we change API
./zephyr/drivers/ipm/ipm_mcux.c:94:	if (size > MCUX_IPM_DATA_REGS * sizeof(uint32_t)) {
./zephyr/drivers/ipm/ipm_mcux.c:117:	return MCUX_IPM_DATA_REGS*sizeof(uint32_t);
Binary file ./zephyr/drivers/ipm/.ipm_mcux.c.swp matches

174 /**
175  * @brief Return the maximum number of bytes possible in an outbound message.
176  *
177  * IPM implementations vary on the amount of data that can be sent in a
178  * single message since the data payload is typically stored in registers.
179  *
180  * @param ipmdev Driver instance pointer.
181  *
182  * @return Maximum possible size of a message in bytes.
183  */
184 __syscall int ipm_max_data_size_get(const struct device *ipmdev);
185 
186 static inline int z_impl_ipm_max_data_size_get(const struct device *ipmdev)
187 {
188         const struct ipm_driver_api *api =
189                 (const struct ipm_driver_api *)ipmdev->api;
190 
191         return api->max_data_size_get(ipmdev);
192 }

Following in-tree Zephyr driver shows all the MCUX mailbox API routine prototypes, with explanatory comments, and shows Zephyr's `z_impl_` convention of naming device API function wrappers with names that begin with this pattern:

zephyr/include/zephyr/drivers$ vi ipm.h

Some other processors have greater data sizes which can be passed via their mailboxes, as indicated in this file:

zephyr/drivers/ipm/Kconfig.imx