Dynamic Voltage Scaling for -2LI and -2LLI Graded Parts - 2023.2 English

Versal Adaptive SoC System Software Developers Guide (UG1304)

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2023.2 English

Versal devices that are graded as -2LI and -2LLI parts need their supplied VCCINT voltage adjusted dynamically based on the operating junction temperature. The Dynamic Voltage Scaling (DVS) of VCCINT power rail allows these parts to operate in the defined industrial temperature range of -40°C to 100°C. When the junction temperature falls below 10°C, the VCCINT voltage needs to be raised to 0.725V. When the temperature reaches 25°C, the VCCINT voltage can be lowered to 0.7V. The following diagram depicts the expected voltage vs. junction temperature change:

Figure 1. DVS Hysteresis

The junction temperature of Versal devices is measured by SysMon and can be obtained from its internal register (DEVICE_TEMP_MAX) or from its I/O interface. PLM firmware can directly manage the DVS of VCCINT power rail or notify an external proxy to manage the -2LI and -2LLI parts. For direct DVS control, the board design must use an I2C controllable voltage regulator module (VRM) for generating VCCINT. The I2C controller of the PMC is used to control the external VRM. PLM monitors the internal register of the SysMon and based on the current junction temperature, it adjusts the external VRM through its I2C connection. If an external proxy, such as a system controller, is responsible for managing the DVS of VCCINT power rail, PLM firmware uses the GPIO controller of the PMC to notify the external proxy as to when to make that adjustment.

Figure 2. SysMon VRM

When enabled, PLM reads the DEVICE_TEMP_MAX register periodically (every 100 ms) and adjusts the VCCINT. Information on the upper and lower temperatures and voltages governing the algorithm needs to be provided to PLM through the CDO file. Inclusion of this CDO file in building the bootable image (PDI) enables the DVS feature in PLM. The CDO should contain two sets of information: how to reach and modify the VOUT of the external VRM, and what are the temperature and voltage thresholds. The following CDO entries are relevant to VCK190 Evaluation Board and they indicate to PLM on how VCCINT regulator on board can be accessed. CDO entries for directly managing the DVS of VCCINT power rail using I2C interface:

# VCCINT Power Regulator on VCK190
pm_add_node 0x442c001 0x460101 0x1822402d 0x10174
# Four power modes for VCCINT_PL rail: 0 - OFF, 1 - ON, 2 - LOWER (0.70v), 3 - UPPER (0.725v)
pm_add_node 0x4328030 0x1 0x442c001 0x4 0x300 0x2010002 0x1021a02 0 0x301 0x2000002 0x1021a02 0x80 0x402 0x2000002 0x21030001 0x10200b3 0x80 0x403 0x2000002 0x21030001 0x10200ba 0x80

CDO entries for notifying an external proxy as to when to mange the VCCINT power rail. On the VCK190 board, the MIO37 pin is a GPIO line that connects a Versal device to the system controller:

# VCCINT Power Regulator on VCK190
pm_add_node 0x442c001 0x2 0x1822402c
# Two power modes for VCCINT_PL rail: 2 - LOWER (0.70v), 3 - UPPER (0.725v)
# Power modes: MIO37 = 0x0, MIO37 = 0x1
pm_add_node 0x4328030 0x4 0x442c001 0x2 0x302 0x44 0x800 0x0 0x303 0x44 0x800 0x800
# Lower Threshold: 10°C (0x500); Upper Threshold: 25°C (0xc80)
pm_add_node 0x4328030 0x3 0x500 0x3 0xc80 0x2

For more details on how the above CDO entries have been derived, refer to Answer Record (000034736).