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libbb/speed_table.c: expand comments

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Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko
2016-09-26 14:37:12 +02:00
parent 4537f83d52
commit 525209ac94
1 changed files with 16 additions and 1 deletions
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17
libbb/speed_table.c
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@@ -103,8 +103,23 @@ static const struct speed_map speeds[] = {
{B4000000, 4000000/200 + 0x8000u}, {B4000000, 4000000/200 + 0x8000u},
#endif #endif
/* 4000000/200 = 0x4e20, bit#15 still does not interfere with the value */ /* 4000000/200 = 0x4e20, bit#15 still does not interfere with the value */
/* (can use /800 if higher speeds would appear, /1600 won't work for B500000) */
}; };
/*
* TODO: maybe we can just bite the bullet, ditch the table and use termios2
* Linux API (supports arbitrary baud rates, no Bxxxx mess needed)? Example:
*
* #include <asm/termios.h>
* #include <asm/ioctls.h>
* struct termios2 t;
* ioctl(fd, TCGETS2, &t);
* t.c_ospeed = t.c_ispeed = 543210;
* t.c_cflag &= ~CBAUD;
* t.c_cflag |= BOTHER;
* ioctl(fd, TCSETS2, &t);
*/
enum { NUM_SPEEDS = ARRAY_SIZE(speeds) }; enum { NUM_SPEEDS = ARRAY_SIZE(speeds) };
unsigned FAST_FUNC tty_baud_to_value(speed_t speed) unsigned FAST_FUNC tty_baud_to_value(speed_t speed)
@@ -114,7 +129,7 @@ unsigned FAST_FUNC tty_baud_to_value(speed_t speed)
do { do {
if (speed == speeds[i].speed) { if (speed == speeds[i].speed) {
if (speeds[i].value & 0x8000u) { if (speeds[i].value & 0x8000u) {
return ((unsigned long) (speeds[i].value) & 0x7fffU) * 200; return ((unsigned)(speeds[i].value) & 0x7fffU) * 200;
} }
return speeds[i].value; return speeds[i].value;
} }