FreeCalypso > hg > freecalypso-tools
view target-utils/libcommon/cmd_baud_switch.c @ 407:19e5a3e2f9c0
fcup-settime: moved time() retrieval a little closer to the output
A fundamental problem with all simple time transfer tools is that there is
always some delay between the time retrieval on the source system and that
transmitted time being set on the destination, and the resulting time
on the destination system is off by that delay amount. This delay cannot
be fully eliminated when working in a simple environment like ours,
but we should make our best effort to minimize it. In the present case,
moving the atinterf_init() call before the time() retrieval should make
a teensy-tiny improvement.
author | Mychaela Falconia <falcon@freecalypso.org> |
---|---|
date | Sat, 11 Aug 2018 21:52:17 +0000 |
parents | 2b041d57de1f |
children |
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/* * Baud rate switching command */ #include <stdlib.h> #include "types.h" #include "ns16550.h" extern struct ns16550_regs *uart_base; extern int serial_in_poll(); static const struct tab { int baud; int divisor; } rate_table[] = { /* * First support the rates and divisors implemented by the * Calypso boot ROM. Dividing 13 MHz by 7 gives an approximation * of 115200 (x16); the divisors used by the boot ROM code for * the slower baud rates are all 7x the usual PC value. */ {115200, 7}, {57600, 7 * 2}, {38400, 7 * 3}, {28800, 7 * 4}, {19200, 7 * 6}, /* * Going faster than ~115200 baud means using a divisor * less than 7, resulting in a non-standard baud rate. * The /1, /2 and /4 seem like reasonable choices. */ {812500, 1}, {406250, 2}, {203125, 4}, /* that's all we really need to support */ {0, 0} }; /* * The following helper function actually switches the UART * baud rate divisor. Call serial_flush() first. It returns the * old divisor value. * * Note the u8 type for both the new and old divisor values. * All supported divisors are well below 255, so we don't bother * with the upper byte. */ static u8 actually_switch_baud(newdiv) u8 newdiv; { volatile struct ns16550_regs *regs; u8 save_lcr, save_old_baud; regs = uart_base; save_lcr = regs->lcr; regs->lcr = save_lcr | NS16550_LCR_DLAB; save_old_baud = regs->datareg; regs->datareg = newdiv; regs->lcr = save_lcr; return(save_old_baud); } void cmd_baud_switch(argbulk) char *argbulk; { char *argv[2]; int baudarg; const struct tab *tp; u8 save_old_baud; int c; if (parse_args(argbulk, 1, 1, argv, 0) < 0) return; baudarg = atoi(argv[0]); for (tp = rate_table; tp->baud; tp++) if (tp->baud == baudarg) break; if (!tp->baud) { printf("ERROR: invalid/unimplemented baud rate argument\n"); return; } /* do it */ serial_flush(); save_old_baud = actually_switch_baud(tp->divisor); /* * After getting the echo of this command at the old baud rate * (see the serial flush call just before switching the divisor), * the line will go silent from the user's perspective. * The user should wait just a little bit, then send us a 0x55 ('U') * at the new baud rate - we should be in the below loop waiting * for this character by then. Receiving that character * correctly (0x55 was chosen for the bit pattern - unlikely to * be received if the sender is sending at a wrong baud rate) * will cause us to conclude this command and return a new '=' * prompt at the new baud rate. * * If we get something else, we assume that someone messed up, * switch back to the old baud rate, scribble an error message * and return. */ do c = serial_in_poll(); while (c < 0); if (c != 0x55) { actually_switch_baud(save_old_baud); printf("ERROR: no \'U\' received, switched back to old baud rate\n"); } }