16. General Purpose Input Output Controller

This chapter provides details of the General Purpose Input Output (GPIO) controller instantiated in the design. The GPIO controller is a memory mapped device and provides a low-level software configruation of the actual general purpose IO cells/pads available in this design.

16.1. IP Details and Available Configuration

Table 16.1 provides details of the source of the IP and and details of the memory map.

Table 16.1 GPIO IP details

	Value
Provider	gitlab
Vendor	incoresemi
Library	blocks/devices
Version	1.0.0
Ip Type	memory_mapped
Numer of Config Registers	19
Direct Memory Region	None
Configuration Register Alignment (bytes)	4

Table 16.2 provides information of the various parameters of the IP available at design time and their description

Table 16.2 GPIO IP Configuration Options

Configuration	Options	Description
Bus interfaces	APB, AXI4L, AXI4	Choice of bus interface protocol supported on this IP
Base address	Integer	The base address where the memory map of the configuration register starts
Bytes reserved	Integer >= 0X4C	The number of bytes reserved for this instance. This can be much larger than the actual bytes required for the configuration registers but cannot be smaller than the value indicated.
ionum	Integer > 1 and < 32	defines the number of GPIOs to be controlled by the instance. Must be >1 and < 32.

16.2. GPIO Instance Details

Table 16.3 shows the values assigned to parameters of this instance of the IP.

Table 16.3 GPIO Instance Parameters and Assigned Values

Parameter Name	Value Assigned
Base Address	0X20000
Bound Address	0X200FF
Bytes reserved	0XFF
Bus Interface	APB
ionum	0X10

16.3. Register Map

The register map for the GPIO control registers is shown in Table 16.4.

Table 16.4 GPIO Register Mapping for all configuration registes

Register-Name	Offset(hex)	Size(Bits)	Reset(hex)	Description
input_val	0X0	16	0X0	This register holds the IO cell input pin value
input_enable	0X4	16	0X0	This register drives the input enable pin of the IO cell
output_val	0X8	16	0X0	This register drives the output value pin of the IO cell
output_en	0XC	16	0X0	This register drives the output enable pin of the IO cell
pullup_en	0X10	16	0X0	Controls the internal pull of the respective IO cells
drive_0	0X14	16	0X0	Controls the drive strength of the respective IO cells
rise_ie	0X18	16	0X0	Enables interrupt when the input val of the IO cell sees a rising edge
rise_ip	0X1C	16	0X0	Indicates a pending interrupt due a rising edge detected on the respective IO cell
fall_ie	0X20	16	0X0	Enables interrupt when the input val of the IO cell sees a falling edge
fall_ip	0X24	16	0X0	Indicates a pending interrupt due a rising edge detected on the respective IO cell
high_ie	0X28	16	0X0	Enables interrupt when the input val of the IO cell sees a value of 1
high_ip	0X2C	16	0X0	Indicates a pending interrupt due a 1 being detected on the respective IO cell
low_ie	0X30	16	0X0	Enables interrupt when the input val of the IO cell sees a value of 0
low_ip	0X34	16	0X0	Indicates a pending interrupt due a 0 being detected on the respective IO cell
set_out	0X38	16	0X0	Attempts to drive the output of IO cell high irrespective of the value of output_val register.
clr_out	0X3C	16	0X0	Attempts to drive the output of IO cell low irrespective of the value of output_val register.
xor_out	0X40	16	0X0	Attempts to drive the IO cell with the inverted value of the output_val register.
drive_1	0X44	16	0X0	Extra bits to control the drive strength of the respective IO cells
drive_2	0X48	16	0X0	Extra bits to control the drive strength of the respective IO cells

All addresses not mentioned in the above table within Base Address and Bound Address are reserved and accesses to those regions will generate a slave error on the bus interface

If ionum parameter is less than 32, then the upper bits of the registers are not used i.e. writes will have no effect on them and will always be read as zeros

The register access attributes for the GPIO control registers are shown in Table 16.5.

Table 16.5 GPIO Register Access Attributes for all configuration Registers

Register-Name	Access Type	Reset Type	Min Access	Max Access
input_val	read-only	synchronous	1B	4B
input_enable	read-write	synchronous	1B	4B
output_val	read-write	synchronous	1B	4B
output_en	read-write	synchronous	1B	4B
pullup_en	read-write	synchronous	1B	4B
drive_0	read-write	synchronous	1B	4B
rise_ie	read-write	synchronous	1B	4B
rise_ip	read-write	synchronous	1B	4B
fall_ie	read-write	synchronous	1B	4B
fall_ip	read-write	synchronous	1B	4B
high_ie	read-write	synchronous	1B	4B
high_ip	read-write	synchronous	1B	4B
low_ie	read-write	synchronous	1B	4B
low_ip	read-write	synchronous	1B	4B
set_out	read-write	synchronous	1B	4B
clr_out	read-write	synchronous	1B	4B
xor_out	read-write	synchronous	1B	4B
drive_1	read-write	synchronous	1B	4B
drive_2	read-write	synchronous	1B	4B

Table 16.6 captures the side-effects caused to either reads or writes on certain registers.

Table 16.6 GPIO Register Side Effects

Register-Name	Read Side Effects	Write Side Effects
rise_ip	none	writing a value of 1 clears the respective pending interrupt
fall_ip	none	writing a value of 1 clears the respective pending interrupt
high_ip	none	writing a value of 1 clears the respective pending interrupt
low_ip	none	writing a value of 1 clears the respective pending interrupt

Note

Registers not included in the Side Effects table have no side-effects generated either on a read or a write.

16.4. Input/Output Values

The GPIOs can be configured in a bit-wise fashion, allowing any pad to act as an input or output by controlling the input_enable and output_enable registers. The effect of setting both is defined by the PADs. The values written to the output_val registers are reflected directly on the GPIO pads. The input values from the GPIO pads is received in the input_val register after 2 consecutive cycles if the input hasn’t changed.

16.5. Interrupts

A single interrupt bit can be generated for each GPIO bit. The controller supports generation of four different kind of interrupts:

1. rise interrupts: These interrupts are generated when the corresponding GPIO bit in input_val detects a rising edge and the correspdoning bit in rise_ie is set.
2. fall interrupts: These interrupts are generated when the corresponding GPIO bit in input_val detects a falling edge and the correspdoning bit in fall_ie is set.
3. high interrupts: These interrupts are generated when the corresponding GPIO bit in input_val if held high and the correspdoning bit in high_ie is set.
4. low interrupts: These interrupts are generated when the corresponding GPIO bit in input_val if held low and the correspdoning bit in low_ie is set.

Since the inputs are synchronized before being sampled by the interrupt logic, it is expected that input pulse width at the GPIO pads is long enough to be detected by the synchronization logic.

Note

A single GPIO can be configured to detect none, any or all types of the above defined interrupts by setting the appropriate bits in the *_ie regsiters of the IP.

Once the interrupt is pending it will remain set until a 1 is written to the appropriate *_ip registers at the corresponding bit location.

These interrupt pins can be routed to the PLIC, or connected to local interrupts of the hart.

16.6. Output Logic Locking

The GPIO pads’ output values can be locked to high, low or track an inverted version of the output_val by controlling the registers set_out, clr_out and xor_out respectively. It is possible to set the same bit location in all the above registers, in which case the GPIO pad is driven the following logic:

gpio_pad_out =  ( ( (output_val & ~clr_out ) | set_out ) ^ xor_out )

16.7. IO and Sideband Signals

The following table describes the io-signals generated from this IP that may directly or indirectly drive certain IO pads.

Table 16.7 GPIO generated IO signals

Signal Name (RTL)	Size	Direction	Description
gpio_in_en	16	output	connected to the input_enable of the IO cells
gpio_out_val	16	output	connected to the output_value of the IO cells
gpio_out_en	16	output	connected to the output_enable of the IO cells
gpio_pull_en	16	output	connected to the internal pull up control of the IO cells
gpio_drive_0	16	output	connected to the drive strength control of the IO cells
gpio_drive_1	16	output	connected to the drive strength control of the IO cells
gpio_drive_2	16	output	connected to the drive strength control of the IO cells
gpio_in_val	16	input	connected to the input value of the IO cell

Note

some of these signals may be muxed with other functional IO from different ips and users should refer to any pinmux module available on chip