I think you are confusing byte ordering with bit ordering, the IEEE
802.15.4 frame format uses little-endian _byte_ ordering, so the least
significant byte comes first. But inside each byte, the least
significant bit has number 0, the most significant bit has number 7.
Therefore, a byte where only bit number 4 is set (written 1 << 4 in
C), is equal to 0x10.
/Joakim
On Wed, Nov 27, 2019 at 2:16 PM Aboodi Ahed Hussein Ali
<abo...@student.usm.my> wrote:
>
> Thank you, Joakim, but I don't think it is correct.
>
> Starting from 0, bit No. 3 of the IEEE802154_FCF_VERS_V1 (Hex 0x10 or binary:
> 0001 0000) have the value 1, thus 0 to 3 represent 8 to 11 on buf[1].
> therefor, the bit No. 3, in 0x10, is set on bit No. 11 of the FCF.
>
> Not sure if the below illustration will be on a layout.
> ---buf[0] buf[1]
> 0000 0000 0000 0000 <-- FCF
> ------------- 0001 0000 <-- IEEE802154_FCF_VERS_V1
>
> This means that the Frame version is not really set probably or this file
> "RIOT/sys/net/link_layer/ieee802154/ieee802154.c" follows a different FCF
> format!!
>
> Am I correct or did I misunderstand that?
>
> Ahed
> ________________________________
> From: Aboodi Ahed Hussein Ali
> Sent: Wednesday, November 27, 2019 5:58 AM
> To: RIOT OS developers list <devel@riot-os.org>
> Subject: IEEEE 802.15.4 FCF Format in
> "RIOT/sys/net/link_layer/ieee802154/ieee802154.c"
>
> Hi all,
>
> I am having a hard time understanding how the "ieee802154_set_frame_hdr"
> function, found in this link, sets the Frame Control Field (FCF) for 802.15.4
> frame header.
> Following the IEEE 802.15.4 FCF format, frame version should be at the
> 12-13th bit of the 2-byte FCF, while in the function code, the frame version
> was set at the 11th bit. Does it uses different FCF format or am I missing
> something?
>
> This is the first part of the function:
>
> size_t ieee802154_set_frame_hdr(uint8_t *buf, const uint8_t *src, size_t
> src_len,
> const uint8_t *dst, size_t dst_len,
> le_uint16_t src_pan, le_uint16_t dst_pan,
> uint8_t flags, uint8_t seq)
> {
> int pos = 3; /* 0-1: FCS, 2: seq */
> uint8_t type = (flags & IEEE802154_FCF_TYPE_MASK);
>
> buf[0] = flags;
> buf[1] = IEEE802154_FCF_VERS_V1; // IEEE802154_FCF_VERS_V1 is
> defined as 0x10
>
> if (((src_len != 0) && (src == NULL)) ||
> ((dst_len != 0) && (dst == NULL))) {
> return 0;
> }
> ...
> ...
>
> The first two bytes of the *buf represent the FCF. I would appreciate it if
> someone explains or provides the FCF format that RIOT-OS uses.
>
> Thank you,
> Ahed
>
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> devel@riot-os.org
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