hollalinux
/
linux-sg2042
mirror of https://github.com/sophgo/linux-riscv.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

[media] iguanair: explain tx carrier setup 

Just comments. No functional changes.

Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
This commit is contained in:
Sean Young 2014-01-20 19:10:38 -03:00 committed by Mauro Carvalho Chehab
parent 123a17d142
commit dd3a5a1e7a
1 changed files with 11 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
drivers/media/rc/iguanair.c
View File

@ -286,10 +286,10 @@ static int iguanair_receiver(struct iguanair *ir, bool enable)
}
/*
* The iguana ir creates the carrier by busy spinning after each pulse or
* space. This is counted in CPU cycles, with the CPU running at 24MHz. It is
* The iguanair creates the carrier by busy spinning after each half period.
* This is counted in CPU cycles, with the CPU running at 24MHz. It is
* broken down into 7-cycles and 4-cyles delays, with a preference for
* 4-cycle delays.
* 4-cycle delays, minus the overhead of the loop itself (cycle_overhead).
*/
static int iguanair_set_tx_carrier(struct rc_dev *dev, uint32_t carrier)
{
@ -316,7 +316,14 @@ static int iguanair_set_tx_carrier(struct rc_dev *dev, uint32_t carrier)
sevens = (4 - cycles) & 3;
fours = (cycles - sevens * 7) / 4;
/* magic happens here */
/*
* The firmware interprets these values as a relative offset
* for a branch. Immediately following the branches, there
* 4 instructions of 7 cycles (2 bytes each) and 110
* instructions of 4 cycles (1 byte each). A relative branch
* of 0 will execute all of them, branch further for less
* cycle burning.
*/
ir->packet->busy7 = (4 - sevens) * 2;
ir->packet->busy4 = 110 - fours;
}