AXI Fan Control#

The AXI Fan Control IP core is a software programmable fan controller. Its purpose is to control the fan used for the cooling of an AMD Xilinx Zynq Ultrascale+ MPSoC without the need of any external temperature sensors. To achieve this, the IP core uses the PL SYSMONE4 primitive to obtain the PL temperature via the DRP interface. Based on the temperature readings, it then outputs a PWM signal to control the fan rotation accordingly. The tacho signal coming from the fan is also measured and evaluated to ensure that the RPM is correct and the fan is working properly.

Features#

AXI Lite control/status interface
Allows interpolation by 10/100/1000/10000/100000 with filtering
Allows arbitrary zero-hold interpolation
Filtering is implemented by a 6-section CIC programmable rate filter and a compensation FIR filter.

Files#

Name	Description
library/axi_fan_control/axi_fan_control.v	Verilog source for the peripheral.

Block Diagram#

Configuration Parameters#

Name	Description	Default Value
`ID`	ID of the core instance	`0`
`PWM_FREQUENCY_HZ`	Frequency of the PWM signal	`5000`
`INTERNAL_SYSMONE`	Determines the source of the temperature information. `0` means temperature is read from ‘temp_in’ port.	`0`
`AVG_POW`	Specifies the number of tacho measurements (`2^AVP_POW`) before averaging them. 7 is the highest possible value.	`7`
`TACHO_TOL_PERCENT`	Tolerance of tacho thresholds when evaluating measurements.	`25`
`TACHO_T25`	Nominal tacho period at 25% PWM.	`1470000`
`TACHO_T50`	Nominal tacho period at 50% PWM.	`820000`
`TACHO_T75`	Nominal tacho period at 75% PWM.	`480000`
`TACHO_T100`	Nominal tacho period at 100% PWM.	`340000`
`TEMP_00_H`	Temperature threshold in degrees Celsius below which PWM should be 0%.	`5`
`TEMP_25_L`	Temperature threshold in degrees Celsius above which PWM should be 25%.	`20`
`TEMP_25_H`	Temperature threshold in degrees Celsius below which PWM should be 25%.	`40`
`TEMP_50_L`	Temperature threshold in degrees Celsius above which PWM should be 50%.	`60`
`TEMP_50_H`	Temperature threshold in degrees Celsius below which PWM should be 50%.	`70`
`TEMP_75_L`	Temperature threshold in degrees Celsius above which PWM should be 75%.	`80`
`TEMP_75_H`	Temperature threshold in degrees Celsius below which PWM should be 75%.	`90`
`TEMP_00_L`	Temperature threshold in degrees Celsius above which PWM should be 100%.	`95`

Interface#

s_axi

AXI Slave Memory Map interface.

Physical Port	Logical Port	Direction
`s_axi_awaddr`	`AWADDR`	in [15:0]
`s_axi_awprot`	`AWPROT`	in [2:0]
`s_axi_awvalid`	`AWVALID`	in
`s_axi_awready`	`AWREADY`	out
`s_axi_wdata`	`WDATA`	in [31:0]
`s_axi_wstrb`	`WSTRB`	in [3:0]
`s_axi_wvalid`	`WVALID`	in
`s_axi_wready`	`WREADY`	out
`s_axi_bresp`	`BRESP`	out [1:0]
`s_axi_bvalid`	`BVALID`	out
`s_axi_bready`	`BREADY`	in
`s_axi_araddr`	`ARADDR`	in [15:0]
`s_axi_arprot`	`ARPROT`	in [2:0]
`s_axi_arvalid`	`ARVALID`	in
`s_axi_arready`	`ARREADY`	out
`s_axi_rdata`	`RDATA`	out [31:0]
`s_axi_rresp`	`RRESP`	out [1:0]
`s_axi_rvalid`	`RVALID`	out
`s_axi_rready`	`RREADY`	in

s_axi_aclk

Physical Port	Logical Port	Direction	Dependency
`s_axi_aclk`	`CLK`	in

s_axi_aresetn

Physical Port	Logical Port	Direction	Dependency
`s_axi_aresetn`	`RST`	in

Ports

Physical Port	Direction	Description
`temp_in`	in [9:0]	Input bus for use with System Management Wizzard IP.
`tacho`	in	Tacho generator input.
`irq`	out	Interrupt signal, level high.
`pwm`	out	PWM control signal.

Clocking#

The IP core runs on the AXI clock and requires a frequency of 100MHz.

Detailed Description#

The main features of this IP core are its independent operation and the fact that it does not require an external temperature sensor. All of the mechanisms contained inside the core are controlled by a state machine, so that they do not depend on the software in case the software fails. The state machine uses the temperature it reads from the SYSMONE4 primitive or via the “temp_in” bus to decide the correct PWM duty-cycle. The temperature thresholds and hysteresis have defaults set in hardware and can be modified by the software. The INTERNAL_SYSMONE parameter is used to set the temperature values source, 0 when reading from temp_in and 1 when instantiating the internal SYSMONE primitive.

Running independently#

The hardware can operate with no input from the software; the IP core starts working after the bitstream is loaded, without needing to be brought out of reset. To activate the interrupts, the software must write to the IRQ_MASK register. At this point, the hardware starts operating and a minimal feedback is provided.

There are 9 temperature intervals defined in the hardware as below:

Five of these intervals have only one possible duty-cycle and four of them can have either of the neighbouring values. After reset, the PWM duty-cycle will start as 100%. The state-machine will begin reading the temperature and will decide on the PWM duty cycle depending on which interval the value matches. The PWM duty-cycle will only change when the temperature enters one of the five intervals with a single PWM duty-cycle, while in the other four, the previous duty-cycle will be maintained. In these intervals, its value will depend on whether the temperature is rising or falling. The temperature can be reconfigured by the software.

The temperature is obtained from the PL SYSMONE4 primitive as a 16-bit raw value or from the temp_in bus as 10-bit. The latest reading is in the TEMPERATURE register. To keep the IP as light as possible, the temperature values obtained are used as raw; they are not converted to Celsius. To convert to Celsius, the following formula needs to be used:

Internal SYSMONE4 primitive: Temperature [C] = (ADC × 501.3743 / 2^bits) – 273.6777 (ug580).

Reading from temp_in: Temperature [C] = (ADC *20 - 11195) / 41

There are five configurations described in the hardware, each with a corresponding tacho period +/- 25% tolerance.

Note

The tacho parameters are for a SUNON PF92251B1-000U-S99 fan.

PWM duty-cycle	Nominal tacho period	Tacho tolerance 25%
0%	N/A	N/A
25%	32 ms	8ms
50%	12.8 ms	3.2 ms
75%	7.2 ms	1.8 ms
100%	6.4 ms	1.6 ms

The hardware will evaluate the tacho signal based on the current PWM duty-cycle by comparing the measured value with the interval’s thresholds. i.e. at 50% duty-cycle the tacho period must stay within 9.6 ms and 16 ms.

A time-out is also used to check if there is any tacho signal at all.

Software control and customization#

The software can overwrite the temperature thresholds and the tacho values if needed. The TEMP_00_H -> TEMP_100_L registers can redefine the temperature intervals and the TACHO_25 -> TACHO_100 registers can also be used to redefine tacho values if a different fan is installed. In this case, the TACHO_*_TOL registers must also be written in order to provide tolerances. They must be calculated by the software as % of the nominal value (i.e. 20% of 10000 = 2000).

The software can also set a custom PWM duty-cycle by using the provided registers. All the values inside the PWM/TACHO registers are in clock-cycle periods. The software can provide custom tacho parameters for that desired PWM, if it wants to continue to evaluate the tacho signal. The PWM period can be read from the PWM_PERIOD register and is by default 20000.

i.e. 5KHz -> 20000 * 10 ns = 200 us

The new PWM value must be greater or equal to the value selected by the hardware and less or equal to the PWM period. The software can use the PWM_WIDTH and PWM_PERIOD registers in order to make sure the new value is valid.

After requesting a new duty-cycle, there is a 5-second delay during which the hardware waits for the fan rotation speed to stabilize. The software will then have to provide parameters for the tacho signal in order for the hardware to be able to evaluate it. To do this, the software will have to write the TACHO_PERIOD and TACHO_TOLERANCE registers in that order. The software can read the TACHO_MEASUREMENT register to obtain the new tacho period and derive the tolerance value from it.

A measurement is performed by averaging 2^AVP_POW consecutive tacho period measurements. The time needed to finish a measurement depends on the frequency of the signal.

The software can now use this register to read the new tacho period and then write it to the TACHO_PERIOD register. Then it can write a tolerance value to the TACHO_TOLERANCE register. The hardware will only start to monitor the tacho signal when the tolerance is provided.

Interrupts#

The fan controller supports interrupts to both inform the software of any possible errors and to facilitate the control of the core. There are four interrupt sources:

The PWM_CHANGED interrupt is generated at the end of the 5-second delay after a PWM duty-cycle change request. The request can come either from the software or from the hardware.
The TEMP_INCREASE occurs when the hardware requests a higher PWM width than the curret one, indicating a rise in temperature.
NEW_TACHO_MEASUREMENT is asserted when a tacho measurement cycle is completed and the value is written to the TACHO_MEASUREMENT register. The software can use this interrupt in the process where it requests a new PWM width to obtain tacho information.
The TACHO_ERR interrupt is generated when the tacho signal either fails to stay within its designated frequency interval or does not toggle at all for 5 seconds.

Register Map#

Fan Controller (axi_fan_control) register map

DWORD	BYTE	Reg Name				Description
		BITS	Field Name	Type	Default Value	Description
`0x0`	`0x0`	`VERSION`				Version of the peripheral. Follows semantic versioning. Current version 1.0.61.
		`[31:16]`	`VERSION_MAJOR`	`RO`	`0x0001`
		`[15:8]`	`VERSION_MINOR`	`RO`	`0x00`
		`[7:0]`	`VERSION_PATCH`	`RO`	`0x61`
`0x1`	`0x4`	`PERIPHERAL_ID`
		`[31:0]`	`PERIPHERAL_ID`	`RO`	`ID`	Value of the ID configuration parameter.
`0x2`	`0x8`	`SCRATCH`
		`[31:0]`	`SCRATCH`	`RW`	`0x00000000`	Scratch register useful for debug.
`0x3`	`0xc`	`IDENTIFICATION`
		`[31:0]`	`IDENTIFICATION`	`RO`	`0x46414e43`	Peripheral identification (‘F’, ‘A’, ‘N’, ‘C’).
`0x10`	`0x40`	`IRQ_MASK`
		`[3:3]`	`NEW_TACHO_MEASUREMENT`	`RW`	`0x1`	Masks the TACHO_MEASUREMENT_DONE IRQ.
		`[2:2]`	`TEMP_INCREASE`	`RW`	`0x1`	Masks the TEMP_INCREASE IRQ.
		`[1:1]`	`TACHO_ERR`	`RW`	`0x1`	Masks the TACHO_ERR IRQ.
		`[0:0]`	`PWM_CHANGED`	`RW`	`0x1`	Masks the PWM_CHANGED IRQ.
`0x11`	`0x44`	`IRQ_PENDING`
		`[3:3]`	`NEW_TACHO_MEASUREMENT`	`RW1C`	`0x0`	This bit will be asserted when the hardware has written a new value to the TACHO_MEASUREMENT register if the NEW_TACHO_MEASUREMENT bit in the IRQ_MASK register is not set.
		`[2:2]`	`TEMP_INCREASE`	`RW1C`	`0x0`	This bit will be asserted whenever the HW decides to increase the PWM duty-cycle, indicating a rise in temperature, and if the TEMP_INCREASE bit in the IRQ_MASK register is not set.
		`[1:1]`	`TACHO_ERR`	`RW1C`	`0x0`	This bit will be asserted when a fault related to the tacho signal is detected. This can either mean that the tacho has not toggled in 5 seconds or that the period of the tacho signal is no longer whithin the defined valid interval. Also, the TACHO_ERR bit in the IRQ_MASK register must not be set.
		`[0:0]`	`PWM_CHANGED`	`RW1C`	`0x0`	This bit will be asserted when a 5 second delay expires after the PWM width was changed. The delay is used to allow the fan rotation speed to stabilize. Also, the PWM_CHANGED bit in the IRQ_MASK register must not be set.
`0x12`	`0x48`	`IRQ_SOURCE`
		`[3:3]`	`NEW_TACHO_MEASUREMENT`	`RO`	`0x0`	This bit will be asserted when the hardware has written a new value to the TACHO_MEASUREMENT register.
		`[2:2]`	`TEMP_INCREASE`	`RO`	`0x0`	This bit will be asserted whenever the hardware decides to increase the PWM duty-cycle indicating a rise in temperature.
		`[1:1]`	`TACHO_ERR`	`RO`	`0x0`	This bit will be asserted when a fault related to the tacho signal is detected. This can either mean that the tacho has not toggled in 5 seconds or that the period of the tacho signal is no longer whithin the defined valid interval.
		`[0:0]`	`PWM_CHANGED`	`RO`	`0x0`	This bit will be asserted when a 5 second delay expires after the PWM width was changed. The delay is used to allow the fan rotation speed to stabilize.
`0x20`	`0x80`	`RSTN`
		`[0:0]`	`RSTN`	`RW`	`0x0`	Reset, default is IN-RESET (0x0), software must write 0x1 to bring up the core.
`0x21`	`0x84`	`PWM_WIDTH`
		`[31:0]`	`PWM_WIDTH`	`RW`	`PWM_PERIOD`	This register contains the width of the PWM output signal. By default its value is established by the hardware after reading the temperature. By writing to this register the software can change the value however this is only possible if the requested value is greater than the value selected by the hardware and not exceeding the PWM period.
`0x22`	`0x88`	`TACHO_PERIOD`
		`[31:0]`	`TACHO_PERIOD`	`RW`	`0x00000000`	After using the PWM_WIDTH register to request a different duty-cycle, the software can use this register to define the target period of the tacho signal. This is used together with the TACHO_TOLERANCE register to define an interval for the tacho signal. This register must be written before the TACHO_TOLERANCE register. The hardware will then use this interval to monitor the tacho signal coming from the fan.
`0x23`	`0x8c`	`TACHO_TOLERANCE`
		`[31:0]`	`TACHO_TOLERANCE`	`RW`	`0x00000000`	This register is used together with the TACHO_PERIOD register to define an interval for the fan’s tacho signal. Writing to this register enables the hardware to start monitoring the tacho signal and so it must be written after the TACHO_PERIOD register.
`0x24`	`0x90`	`TEMP_DATA_SOURCE`
		`[31:0]`	`TEMP_DATA_SOURCE`	`RO`	`INTERNAL_SYSMONE`	This register copies the value from the INTERNAL_SYSMONE register and is used to inform the software what the source of the temperature information is.
`0x30`	`0xc0`	`PWM_PERIOD`
		`[31:0]`	`PWM_PERIOD`	`RO`	`0x00004e20`	This register contains the period for the PWM output signal. Derived from the PWM_FREQUENCY_HZ parameter.
`0x31`	`0xc4`	`TACHO_MEASUREMENT`
		`[31:0]`	`TACHO_MEASUREMENT`	`RO`	`0x00000000`	This register contains the measurement results of the tacho signal period performed by the hardware.
`0x32`	`0xc8`	`TEMPERATURE`
		`[31:0]`	`TEMPERATURE`	`RO`	`0x00000000`	This register contains the latest temperature reading from the SYSMONE primitive.
`0x40`	`0x100`	`TEMP_00_H`
		`[31:0]`	`TEMP_00_H`	`RW`	`TEMP_00_H`	Temperature threshold below which PWM should be 0%
`0x41`	`0x104`	`TEMP_25_L`
		`[31:0]`	`TEMP_25_L`	`RW`	`TEMP_25_L`	Temperature threshold above which PWM should be 25%
`0x42`	`0x108`	`TEMP_25_H`
		`[31:0]`	`TEMP_25_H`	`RW`	`TEMP_25_H`	Temperature threshold below which PWM should be 25%
`0x43`	`0x10c`	`TEMP_50_L`
		`[31:0]`	`TEMP_50_L`	`RW`	`TEMP_50_L`	Temperature threshold above which PWM should be 50%
`0x44`	`0x110`	`TEMP_50_H`
		`[31:0]`	`TEMP_50_H`	`RW`	`TEMP_50_H`	Temperature threshold below which PWM should be 50%
`0x45`	`0x114`	`TEMP_75_L`
		`[31:0]`	`TEMP_75_L`	`RW`	`TEMP_75_L`	Temperature threshold above which PWM should be 75%
`0x46`	`0x118`	`TEMP_75_H`
		`[31:0]`	`TEMP_75_H`	`RW`	`TEMP_75_H`	Temperature threshold below which PWM should be 75%
`0x47`	`0x11c`	`TEMP_100_L`
		`[31:0]`	`TEMP_100_L`	`RW`	`TEMP_100_L`	Temperature threshold above which PWM should be 100%
`0x50`	`0x140`	`TACHO_25`
		`[31:0]`	`TACHO_25`	`RW`	`TACHO_T25`	Nominal tacho period at 25% PWM
`0x51`	`0x144`	`TACHO_50`
		`[31:0]`	`TACHO_50`	`RW`	`TACHO_T50`	Nominal tacho period at 50% PWM
`0x52`	`0x148`	`TACHO_75`
		`[31:0]`	`TACHO_75`	`RW`	`TACHO_T75`	Nominal tacho period at 75% PWM
`0x53`	`0x14c`	`TACHO_100`
		`[31:0]`	`TACHO_100`	`RW`	`TACHO_T100`	Nominal tacho period at 100% PWM
`0x54`	`0x150`	`TACHO_25_TOL`
		`[31:0]`	`TACHO_25_TOL`	`RW`	`TACHO_25_TOL`	Tolerance for the 25% PWM tacho period `TACHO_25_TOL = TACHO_T25*TACHO_TOL_PERCENT/100`
`0x55`	`0x154`	`TACHO_50_TOL`
		`[31:0]`	`TACHO_50_TOL`	`RW`	`TACHO_50_TOL`	Tolerance for the 50% PWM tacho period `TACHO_50_TOL = TACHO_T50*TACHO_TOL_PERCENT/100`
`0x56`	`0x158`	`TACHO_75_TOL`
		`[31:0]`	`TACHO_75_TOL`	`RW`	`TACHO_75_TOL`	Tolerance for the 75% PWM tacho period `TACHO_75_TOL = TACHO_T75*TACHO_TOL_PERCENT/100`
`0x57`	`0x15c`	`TACHO_100_TOL`
		`[31:0]`	`TACHO_100_TOL`	`RW`	`TACHO_100_TOL`	Tolerance for the 100% PWM tacho period `TACHO_100_TOL = TACHO_T100*TACHO_TOL_PERCENT/100`

Access Type	Name	Description
RO	Read-only	Reads will return the current register value. Writes have no effect.
RW	Read-write	Reads will return the current register value. Writes will change the current register value.
RW1C	Read,write-1-to-clear	Reads will return the current register value. Writing the register will clear those bits of the register which were set to 1 in the value written. Bits are set by hardware.