Re: [Simulavr-devel] [PATCH] use static callbacks instead of template param for IOReg

[panic]

Hi,

Klaus Rudolph:
> can someone assist me a bit to catch the problem and the background
> please? :-)

sure :-)

> Which controller and which registers on that controller(s) are affected.
> It would be nice if someone points me to two or more different registers
> on a single controller core which provide "new" SBI/CBI functionality.

Example: ATmega644, http://www.atmel.com/Images/doc2593.pdf
  (other example: ATtiny25/45/85)
Initial datasheet revision date: 06/2005
Page 20, section "6.4 I/O Memory" (emphasis mine):
> All ATmega644 I/Os and peripherals are placed in the I/O space. All I/O 
> locations may be
> accessed by the LD/LDS/LDD and ST/STS/STD instructions, transferring data 
> between the 32
> general purpose working registers and the I/O space. I/O Registers within the 
> address range
> 0x00 - 0x1F are *directly bit-accessible* using the SBI and CBI instructions. 
> In these registers, the
> value of *single bits* can be checked by using the SBIS and SBIC instructions.


> Have we more than an SBI/CBI issue? More instructions requiring rework?

AFAIK, it is only the SBI/CBI instruction. Affecting the PINx register
(port pin toggle feature, see below) and clearing of interrupt flags
(see below).

Datasheet page 67, section "12.2.2 Toggling the Pin":
> Writing a logic one to PINxn toggles the value of PORTxn, independent on the 
> value of DDRxn.
> Note that the SBI instruction can be used to *toggle one single bit* in a 
> port.

Page 20, section "6.4 I/O Memory":
> Some of the Status Flags are cleared by writing a logical one to them. Note 
> that, unlike most
> other AVRs, the CBI and SBI instructions will only operate on the specified 
> bit, and can therefore
> be used on registers containing such Status Flags. The CBI and SBI 
> instructions work with reg-
> isters 0x00 to 0x1F only.

> It would also be nice if the "new" functionality is described in a few
> words and the wrong effect we currently have implemented. A direct
> reference to datasheet is highly welcome.

Currently SBI/CBI are implemented as "read/modify/write" (as if
in/or/out instructions were used). However, this differs from a true
"bit-accessible I/O register".

Example: PINx toggle feature

DDRB = 0xff;
PORTB = 0xff;
PINB |= _BV(PB0); // sbi _SFR_IO_REG(PINB), 0

Expected behaviour:
  PB0 toggles from 1 -> 0
PINB is a bit-accessible IO register. The SBI instruction behaves as if
0x01 had been written.

Simulavr behaviour:
  All bits (PB7..PB0) toggle from 1 -> 0.
Simulavr emulates SBI as RMW:
- Read PINB: 0xff (each input stage=1)
- Modify: 0xff | 0x01 --> 0xff
- Write: 0xff --> PINB, == "PORTB ^= 0xff"

The PINx toggle feature can also be used to toggle pullups ("independent
on the value of DDRxn").

Similarly, SBI on an interrupt flag register with multiple interrupt
flags set, would also clear these other interrupt flags.
Another example: SBI on a non-interrupt bit would clear (i.e. write 1
to) an interrupt flag in the same register (because the interrupt flag
is read as 1, other bit is ORed, result with interrupt bit set is
written back).

Cheers,
panic