CAPSENSE™ Touchpad I2C Host porting guide

Overview

The CAPSENSE™ Touchpad I2C Host middleware is platform independent. Platform-specific functionality is implemented in the port/ directory.

The repository currently provides the following ports:

port/
├── psoc_edge/
│   ├── mtb_touchpad_i2c_port.c
│   └── mtb_touchpad_i2c_port.h
└── template/
    ├── mtb_touchpad_i2c_port_template.c
    └── mtb_touchpad_i2c_port_template.h

Developers targeting other platforms should use the PSOC Edge implementation as a reference, and the template/ files as a starting point.

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Port Layer Responsibilities

A platform port must provide implementations of the following functions:

uint32_t touchpad_i2c_init(void);
 
uint32_t touchpad_i2c_read(uint16_t subaddress,
                           uint8_t *data,
                           uint16_t length,
                           void *intf_ptr);
 
uint32_t touchpad_i2c_write(uint16_t subaddress,
                            uint8_t *data,
                            uint16_t length,
                            void *intf_ptr);

These functions are responsible for:

• Initializing the platform I2C peripheral
• Reading data from the touchpad over I2C
• Writing data to the touchpad over I2C

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Reference Implementation

The PSOC Edge implementation uses the PDL SCB I2C driver:

• Cy_SCB_I2C_Init()
• Cy_SCB_I2C_MasterRead()
• Cy_SCB_I2C_MasterWrite()
• Cy_SCB_I2C_Enable()

Equivalent APIs from another platform may be used instead.

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Required I2C Transactions

Register Read

START
Slave Address + Write
Register Address MSB
Register Address LSB
REPEATED START
Slave Address + Read
Read N bytes
STOP

Register Write

START
Slave Address + Write
Register Address MSB
Register Address LSB
Write N bytes
STOP

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Platform Configuration

Platform-specific configuration should remain in the port layer, including:

• I2C peripheral instance
• SDA/SCL pin assignment
• Interrupt configuration
• Interrupt priority
• I2C clock frequency must be 1000 KHz
• Device address is fixed and it is 0x0D

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Creating a New Port

1. Copy the files from the template/ directory and rename them to match the target platform.
2. Implement the platform-specific I2C APIs in the marked TODO sections, using the PSOC Edge port as a reference.
3. Keep the same public function prototypes.
4. No changes should be required in the portable middleware core.