On Tue, Apr 11, 2017 at 10:12:32PM +0200, Rodolfo Giometti wrote:
> Multidrop mode differentiates the data characters and the address
> characters. Data is transmitted with the parity bit to 0 and addresses
> are transmitted with the parity bit to 1.
>
> Usually multidrop is implemented by forcing MARK and SPARE parity as follow:
> /* Write data */
>
> /* Address byte */
> term.c_cflag |= PARENB | CMSPAR | PARODD; /* MARK(1) */
> ret = tcsetattr(fd, TCSADRAIN, &term);
> if (ret < 0) {
> perror("unable to set MARK");
> exit(-1);
> }
> buf[0] = 0x00;
> ret = writen(fd, buf, 1);
> if (ret < 0) {
> perror("unable to write address (%m)");
> exit(-1);
> }
>
> /* Data bytes */
> term.c_cflag |= PARENB | CMSPAR; /* SPACE(0) */
> term.c_cflag &= ~PARODD;
> ret = tcsetattr(fd, TCSADRAIN, &term);
> if (ret < 0) {
> perror("unable to set SPACE");
> exit(-1);
> }
> buf[0] = 0x1c;
> buf[1] = 0x01;
> buf[2] = 0x01;
> buf[3] = 0x00;
> buf[4] = 0x01;
> buf[5] = 0xde;
> buf[6] = 0xd4;
> ret = writen(fd, buf, 7);
> if (ret < 0) {
> perror("unable to write data (%m)");
> exit(-1);
> }
>
> However this usually slow down communication by adding a delay between
> the first byte and the others.
>
> The first attached patch defines two non-stadard bits PARMD (that
> enables multidrop) and SENDA (that marks the next transmitted byte as
> address) that can be used to completely remove the delay by correctly
> managing the parity bit generation in hardware (the second patch is
> for SAMA5D3 CPU). Then the userland code becomes:
>
> /* Transmission: enable parity multidrop and mark 1st byte as address */
> term.c_cflag |= PARENB | CMSPAR | PARMD | SENDA;
> ret = tcsetattr(fd, TCSADRAIN, &term);
> if (ret < 0) {
> perror("unable to set MARK");
> exit(-1);
> }
>
> /* Write data */
> n = 0;
> buf[n++] = 0x00;
> buf[n++] = 0x1c;
> buf[n++] = 0x01;
> buf[n++] = 0x01;
> buf[n++] = 0x00;
> buf[n++] = 0x01;
> buf[n++] = 0xde;
> buf[n++] = 0xd4;
> ret = writen(fd, buf, n);
> if (ret < 0) {
> perror("unable to write data (%m)");
> exit(-1);
> }
>
> Rodolfo
Why isn't this info in the changelog text itself?
And this is 'v2', right? Please always properly say that, remember,
maintainers and reviewers have the short-term memory of a squirrel...
thanks,
greg k-h
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