[Oberon] Volatile variables in Oberon

[Jörg Straube]

And in Oberon
   VAR c: BYTE;
   SYSTEM.GET(UART0UDR, c);

Have fun
Jörg

> Am 30.07.2016 um 19:00 schrieb Magnus Karlsson <magnus at saanlima.com>:
> 
> Your C code seems to a bit convoluted if just want to access a register.  
> This is quite often done by defining the registers as volatile pointers like this:
> 
> Register address definitions (in this case for a UART):
> #define UART0_UDR      (*(volatile  uint8_t *)(0x44000000))
> #define UART0_UCR      (*(volatile uint16_t *)(0x44000004))
> #define UART0_UBRR     (*(volatile uint16_t *)(0x44000008))
> 
> You can then access registers like this (read UART data register):
> uint8_t c = UART0_UDR;
> 
> Magnus
> 
>> On 7/29/2016 11:06 PM, Skulski, Wojciech wrote:
>> Chris:
>> 
>>> But Oberon variables are not mapped to registers that can be changed "from
>>> the other end". The explicit operations SYSTEM.GET and SYSTEM.PUT are used
>>> when you want to transfer data between a peripheral register (mapped to an
>>> absolute memory location) and Oberon variables.
>>  Pardon my C on this mailing list. The point I want to make is that it is ugly. 
>> 
>> Here is a sample of my C program where I am reading from an absolute memory location mapped to an FPGA register. The "target" is an integer, which is then used to retrieve a value from the FPGA. The address is not constant, but I can make it constant using a #define.
>> 
>>  long target; /* long int holds addr, needs a typecast */
>>  short value;
>>  short *virt_saddr;	/* typed pointer to 16-bit short */
>> 
>>  virt_saddr = (short *) target; /* convert target to pointer */
>>  value = * virt_saddr;            /* read value from address   */
>> 
>> I would prefer to write in C something like the following:
>>  
>>  short value at address; /* address is constant, which is most often the case*/
>> 
>> In Oberon it would be something like this:
>> 
>>  CONST address = ....; 
>>   VAR value: INTEGER AT address; (* address must be constant*)
>> 
>> Now the question, is this unreasonable? 
>> 
>> Wojtek
>> --
>> Oberon at lists.inf.ethz.ch mailing list for ETH Oberon and related systems
>> https://lists.inf.ethz.ch/mailman/listinfo/oberon
>> 
> 
> --
> Oberon at lists.inf.ethz.ch mailing list for ETH Oberon and related systems
> https://lists.inf.ethz.ch/mailman/listinfo/oberon
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