Runtime Telemetry

Chip Management Firmware reserves a region of memory for Metal runtime use. The buffer is zero-initialized at boot, 32-byte aligned, and located in CSM (the tensix_sm / ARC memory space, i.e. within NOC0 8-0).

Scratch Registers

As per the scratch register definitions in status_reg.h (SCRATCH_RAM[0..63]):

Register	SCRATCH_RAM index	Description
RUNTIME_TELEMETRY_ADDR	22 (0x80030458)	CSM address of the runtime telemetry buffer
RUNTIME_TELEMETRY_SIZE	23 (0x8003045C)	Size of the runtime telemetry buffer in bytes

Both values are written once during init and do not change until the next chip reset. For a given CMFW build, the size is fixed at compile time and the address is fixed at link time.

Procedure to Access Runtime Telemetry

Via NOC Access to ARC Memory

1. Read reset_unit.SCRATCH_RAM[23] to obtain the buffer size in bytes. If the size is 0, assume the buffer is unavailable and stop. Older CMFW builds leave this register at 0.

2. Read reset_unit.SCRATCH_RAM[22] to obtain the tile-local address of the buffer.

3. Read or write the buffer via NOC using the address from step 2 and the size from step 1.

Firmware Details

• The buffer is placed in the .bss.runtime_telemetry linker section and is cleared with the rest of BSS during boot.

• Size is controlled by CONFIG_TT_BH_ARC_RUNTIME_TELEMETRY_SIZE (default 1024 bytes). The value must be a positive multiple of 32.

• Address and size are published via SYS_INIT_APP in runtime_telemetry.c.