Re: Compiler doesn't respect 'Size for atomic object

[Robert Eachus <rieachus@comcast.net>]

On Wednesday, December 20, 2017 at 4:20:22 PM UTC-5, Simon Wright wrote:

> I meant, naturally an integral type. The RM description of the NVIC's
> STIR indicates that the IRQ fits in 8 bits; the top 24 bits are reserved
> (write as 0).

A language lawyer reading:  If the hardware specifies that those bit must be zero?  Then it is definitely a bug.  But if all the hardware says is that the positions are reserved, I would expect the compiler to pass whatever junk happened to be in the register.  (In other words, move the IRQ as eight-bits to a register, then pass the register to the hardware.)

Should the address of Register in your example be set to 16#E000EF00#? Also should your type Interrupt_ID be given a size?  If so I would expect the new behavior with Interrupt_ID'Size set to 8, and the old behavior when it is set to 32.

I am certainly not an expert on the Cortex-M CPUs, but as I read the documentation, the STIR is write-only, and the upper 24-bits of the value written there are ignored.  If so, no bug, but probably worth a comment IF the behavior of the compiler has changed, not just the bits you are passing..