DIP62: Volatile type qualifier for unoptimizable variables in embedded programming

[Mike via Digitalmars-d]

On Tuesday, 15 July 2014 at 19:48:23 UTC, Walter Bright wrote:

> The one thing peek/poke doesn't offer is transitivity. C/C++ 
> don't offer volatile transitivity either. I'm not at all sure 
> that anyone builds a data structure in memory-mapped registers, 
> so I'm not convinced this is a need.

Here's an example from the STM32F4 ARM Cortex-M peripheral 
library:

#define __IO volatile

/**
   * @brief DMA Controller
   */

typedef struct
{
   __IO uint32_t CR;     /*!< DMA stream x configuration register  
     */
   __IO uint32_t NDTR;   /*!< DMA stream x number of data register 
     */
   __IO uint32_t PAR;    /*!< DMA stream x peripheral address 
register */
   __IO uint32_t M0AR;   /*!< DMA stream x memory 0 address 
register   */
   __IO uint32_t M1AR;   /*!< DMA stream x memory 1 address 
register   */
   __IO uint32_t FCR;    /*!< DMA stream x FIFO control register   
     */
} DMA_Stream_TypeDef;

typedef struct
{
   __IO uint32_t LISR;   /*!< DMA low interrupt status register,   
    Address offset: 0x00 */
   __IO uint32_t HISR;   /*!< DMA high interrupt status register,  
    Address offset: 0x04 */
   __IO uint32_t LIFCR;  /*!< DMA low interrupt flag clear 
register,  Address offset: 0x08 */
   __IO uint32_t HIFCR;  /*!< DMA high interrupt flag clear 
register, Address offset: 0x0C */
} DMA_TypeDef;

There are several hundreds lines of this stuff in the library.  
It is used to model register banks.  Each register bank roughly 
corresponds to one of the embedded peripherals.

Mike