Hi Wolfgang,
On Tue, Jun 7, 2011 at 3:06 AM, Wolfgang Denk wd@denx.de wrote:
Dear Simon Glass,
In message BANLkTi=+pqk=UQY_=NoXcMabBDm845xcEw@mail.gmail.com you wrote:
#define clrsetfield_le32(bitfield, addr, value) =A0...
Then caller can define these in a header file:
#define FIELD_MASK 0xf0000 #define FIELD_SHIFT 16
And use this macro to set the bitfield to 6, for example:
clrsetfield_le32(FIELD, &my_device->ctrl, 6)
(this will simply shift the value left 16 bits and apply the supplied ma=
sk)
This captures the essence of bitfields, in that we are abstracting the field under a single name. The change would just add this macro to the io.h header file.
Sorry, I fail to understand how you envision to use this, and how it would be different from =A0clrsetbits*() ?
For example this allows us to replace:
clrsetbits_le(&my_device->ctrl, 0xf << 16, 6 << 16)
with:
clrsetfield_le32(FIELD, &my_device->ctrl, 6)
So the two identical shifts are avoided, and the forming of the mask is done once in the define.
If you really insist:
#define FIELD_VAL(x) (x << 16) #define FIELD_MASK FIELD_VAL(0xF)
clrsetbits_le32(&my_device->ctrl, FIELD_MASK, FIELD_VAL(6));
We now have a computed mask which is good, thank you.
But the FIELD is specified twice in the same statement. Can we therefore please take this a step further and write something like this?
clrsetfield_le32(&my_device->ctrl, FIELD, 6);
so:
#define clrsetfield_le32(addr, field, data) clrsetbits_le32(add, field ##_MASK, field ## _VAL(data))
How can we combine these two to remove the redundancy?
In practical use cases, you will probablu not use magg numbers like '6' anyway, and define symbolic names for this anyway, so this would be:
clrsetbits_le32(&my_device->ctrl, FIELD_MASK, FIELD_VAL_FOO);
In our code there is quite a bit of both but yes setting single bit fields to 0 for off, and 1 for on, is common. Also we sometime have things like:
enum { OSC_FREQ_12, OSC_FREQ_16, OSC_FREQ_19_2, OSC_FREQ_24, };
for 2-bit fields (and so on for 3, 4 bit fields).
Regards, Simon
or similar.
Best regards,
Wolfgang Denk
-- DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@denx.de News is what a chap who doesn't care much about anything wants to read. And it's only news until he's read it. After that it's dead. - Evelyn Waugh _Scoop_ (1938) bk. 1, ch. 5