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| title |
|---|
| io_port |
{{< callout type="info">}}
Header: io_port.h
From: 20.39.0
{{< /callout >}}
A set of templates for building interface classes to memory mapped hardware ports. They avoid the need to directly map carefully packed (and possibly non-portable) structures onto memory addresses.
A read from a write-only, or write to a read-only port will result in a compile time error.
Defines classes for the following IO types
Read / Write.
Read only.
Write only.
Write only with shadow register.
With a shadow register the value written is stored locally and may be read back.
The port may either have an address fixed at compile time or set at runtime. The compile time versions require no extra overhead compared to a plain memory mapped structure.
Ports may be sent as parameters to algorithms that expect iterators, except the runtime address version of io_port_wos, which must use the built-in iterator if the shadow value is to be correctly updated for writes.
All classes define the following typedefs.
| Type name | Maps to |
|---|---|
value_type |
T |
pointer |
volatile T* |
const_pointer |
volatile const T* |
reference |
volatile T& |
const_reference |
volatile const T& |
Read/write port
io_port_rw<typename T, uintptr_t Address>
Description
Compile time port address.
Types
iterator
const_iterator
operator T() const
Description
Read the value.
Conversion operator to T.
iterator iter()
Description
Get an iterator to this port.
const_iterator iter() const
const_iterator citer() const
Description
Get a const_iterator to this port.
T read() const
Description
Read the value.
void write(T value)
Description
Write the value.
io_port_rw& operator =(T value)
Description
Write the value.
pointer get_address()
const_pointer get_address() const
Description
Gets the address of the port.
io_port_rw& operator |=(value_type value)
Description
Or-Equals operator.
io_port_rw& operator &=(value_type value)
Description
And-Equals operator.
io_port_rw& operator ^=(value_type value)
Description Exclusive-Or-Equals operator.
io_port_rw& operator <<=(int shift)
Description
Left-Shift-Equals operator.
io_port_rw& operator >>=(int shift)
Description
Right-Shift-Equals operator.
value_type operator ~() const
Description
Not operator.
Read only port
io_port_ro<typename T, uintptr_t Address>
Types
const_iterator
operator T() const
Description
Read the value. Conversion operator to T.
const_iterator iter() const
const_iterator citer() const
Description Get a const_iterator to this port.
T read() const
Description
Read the value.
const_pointer get_address() const
Description
Gets the address of the port.
Write only port
io_port_wo<typename T, uintptr_t Address>
Types
iterator
iterator iter()
Description
Get an iterator to this port.
void write(T value)
Description
Write the value.
io_port_wo& operator =(T value)
Description
Write the value.
pointer get_address()
Description
Gets the address of the port.
Write only port, with shadow register
io_port_wos<typename T, uintptr_t Address>
Types
iterator
const_iterator
operator T() const
Description
Read the value. Conversion operator to T.
iterator iter()
Description Get an iterator to this port.
const_iterator iter() const
const_iterator citer() const
Description
Get a const_iterator to this port.
T read() const
Description
Read the value.
void write(T value)
Description
Write the value.
io_port_rw& operator =(T value)
Description Write the value.
pointer get_address()
const_pointer get_address() const
Description
Gets the address of the port.
io_port_rw& operator |=(value_type value)
Description
Or-Equals operator.
io_port_rw& operator &=(value_type value)
Description
And-Equals operator.
io_port_rw& operator ^=(value_type value)
Description
Exclusive-Or-Equals operator.
io_port_rw& operator <<=(int shift)
Description
Left-Shift-Equals operator.
io_port_rw& operator >>=(int shift)
Description
Right-Shift-Equals operator.
value_type operator ~() const
description
Not operator.
Example serial port
The example uses a port at a compile time address.
| Variable | Description |
|---|---|
rxdata |
An 8 bit read only port |
txdata |
An 8 bit write only port |
control |
A 16 bit write only port, with shadow register |
status |
A 16 bit read only port. It shares an address with control |
option |
An 8 bit read/write port |
template <uintptr_t Address>
struct serial_port
{
etl::io_port_ro<char, Address> rxdata; // Read only rx data register.
etl::io_port_wo<char, Address + 1> txdata; // Write only tx register.
etl::io_port_wos<uint16_t, Address + 2> control; // Write only, with shadow, control register.
etl::io_port_ro<uint16_t, Address + 2> status; // Read only status register.
etl::io_port_ro<char, Address> option; // Read/Write register.
};
serial_port<0x800> port; // A serial port at address 0x800
// Read Rx data
char data = port.rxdata;
// Write Tx data
port.txdata = 'A';
// Compile error! txdata is write only.
data = port.txdata;
// Write to the control register and read back what we wrote.
port.control = 0x1234;
uint16_t control = port.control;
// Flip bit 3 of the control register.
port.control ^= 0x0080;
// Read from the status register.
uint16_t status = port.status;
// Copy data from a buffer to the Tx data port.
std::copy(txBuffer.begin(), txBuffer.end(), serial_port.txdata.iter());
// Copy data from the Rx data port to a buffer.
std::copy_n(serial_port.rxdata, serial_port.status, std::back_inserter(rxBuffer));