On Wed, Jun 7, 2017 at 7:52 AM, Noralf Trønnes noralf@tronnes.org wrote:
Hi Emil,
Den 07.06.2017 11.30, skrev Emil Velikov:
Hi Noralf,
Small drive-by comment, noticed while going through my morning coffee. By no means a full review.
On 2 June 2017 at 12:49, Noralf Trønnes noralf@tronnes.org wrote:
+/* pixels on display are numbered from 1 */ +static void repaper_all_pixels(struct repaper_epd *epd, u8 **pp,
const u8 *data, u8 fixed_value, const u8*mask,
enum repaper_stage stage)+{
unsigned int b;for (b = epd->width / 8; b > 0; b--) {if (data) {u16 pixels = repaper_interleave_bits(data[b -1]);
u16 pixel_mask = 0xffff;if (mask) {u16 pixel_mask =repaper_interleave_bits(mask[b - 1]);
pixel_mask = (pixel_mask ^ pixels) &0x5555;
pixel_mask |= pixel_mask << 1;The second u16 pixel_mask seems very suspicious - likely a copy/paste mistake ?
Actually it's a correct copy. The same pattern is used in three places. I did look at the datasheet to try and understand what was going on, but the current and previous frame is applied in normal and inverted form in several stages, the pixels are converted to black/white/nochange and then I lost track of it all. So I decided that the Pervasive people who wrote the driver probably knew what they where doing. At least it works!
It's doubling up the bits... 0x5555 is a 0101010101010101 pattern, so pixel_mask |= pixel_mask << 1 (after pixel_mask is x & 0x5555) is just saying that the same bit should be repeated twice.
As for why you'd want to do that ... no clue. Maybe it's a 2-bit-per-pixel packed mask and you want to set each pixel to 11 or 00 here?