The PS/2 keyboard driver

Overview

The PS/2 Controller (often called the “Keyboard controller”) is located on the mainboard. In the early days the controller was a single chip (Intel 8042). (Source: https://wiki.osdev.org/I8042_PS/2_Controller)

In BenOS, the PS/2 driver is used to initialize and manage the PS/2 Controller, which is necessary to make the keyboard driver work properly.

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Related files

• kernel/drivers/include/ps2.h
• kernel/drivers/ps2.c

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Constants

All these constants are defined in kernel/drivers/include/ps2.h.

Name	Value	Description
KBD_DATA	0x60	Data port used for commands and responses
KBD_STATUS_OBF	Bit	Output Buffer Full – set when data is ready to be read
KBD_STATUS_IBF	Bit	Input Buffer Full – set when controller is processing
KBD_DISABLE_PORT1	Byte	Command to disable the first PS/2 port
KBD_ENABLE_PORT1	Byte	Command to enable the first PS/2 port
KBD_READ_CONF	Byte	Command to read the controller configuration byte
KBD_WRITE_CONF	Byte	Command to write to the controller configuration byte
KBD_SELF_TEST	Byte	Command to run a self-test of the controller

Initialization flow

The initialization sequence involves:

1. Disabling the first PS/2 port
2. Flushing the output buffer
3. Reading and editing the controller configuration byte
4. Performing the controller self-test
5. Reseting the keyboard
6. Setting the keyboard scancode set

I/O synchronization

The two static functions used for I/O synchronization are:

// Source: kernel/drivers/ps2.c

static void wait_ibf_clear();       // Wait for the input buffer to be clear
static void wait_obf_full();        // Wait for the output buffer to be full

Core functions

There are two core functions, but the first one is used nowhere in the kernel. It is just here because it could be useful for the future.

// Source: kernel/drivers/include/ps2.h

void ps2_set_typematic_rate(uint8_t rate);
void ps2_controller_init();

So ps2_set_typematic_rate() is not used yet. It modifies the typematic rate (in Hz). The most important function of this driver is the second one: ps2_controller_init(). Check the initialization flow to see what it exactly does.

Error handling and warnings

Here are the different handled errors and warnings you can get:

ps2_set_typematic_rate()

[WARN] Failed to set typematic on PS/2 controller This warning may occur if the controller doesn't support typematic rate configuration or is unresponsive.

[WARN] Bad configuration setting for PS/2 controller This indicates an invalid response was received after attempting to set the typematic rate.

ps2_controller_init()

[ERR] PS/2 controller self test failed The controller returned an unexpected result during its self-test.

[ERR] Failed to reset the PS/2 keyboard The keyboard did not acknowledge the reset command.

[WARN] Keyboard didn't acknowledge 0xF0 The keyboard did not acknowledge the 0xF0 command (used to set scancode mode).

[WARN] Keyboard didn't accept Scancode Set 1 The keyboard rejected the requested scancode set. It may still work using the default set (likely 2 or 3).