path: root/firmware/keyspan_pda/keyspan_pda.S

/*  $Id: loop.s,v 1.23 2000/03/20 09:49:06 warner Exp $
 * 
 *  Firmware for the Keyspan PDA Serial Adapter, a USB serial port based on
 *  the EzUSB microcontroller.
 * 
 *  (C) Copyright 2000 Brian Warner <warner@lothar.com>
 * 
 * 	This program is free software; you can redistribute it and/or modify
 * 	it under the terms of the GNU General Public License as published by
 * 	the Free Software Foundation; either version 2 of the License, or
 * 	(at your option) any later version.
 * 
 *  "Keyspan PDA Serial Adapter" is probably a copyright of Keyspan, the
 *  company.
 * 
 *  This serial adapter is basically an EzUSB chip and an RS-232 line driver
 *  in a little widget that has a DB-9 on one end and a USB plug on the other.
 *  It uses the EzUSB's internal UART0 (using the pins from Port C) and timer2
 *  as a baud-rate generator. The wiring is:
 *   PC0/RxD0 <- rxd (DB9 pin 2)         PC4 <- dsr pin 6
 *   PC1/TxD0 -> txd pin 3               PC5 <- ri  pin 9
 *   PC2      -> rts pin 7               PC6 <- dcd pin 1
 *   PC3      <- cts pin 8               PC7 -> dtr pin 4
 *   PB1 -> line driver standby
 *
 *  The EzUSB register constants below come from their excellent documentation
 *  and sample code (which used to be available at www.anchorchips.com, but
 *  that has now been absorbed into Cypress' site and the CD-ROM contents
 *  don't appear to be available online anymore). If we get multiple
 *  EzUSB-based drivers into the kernel, it might be useful to pull them out
 *  into a separate .h file.
 * 
 * THEORY OF OPERATION:
 *
 *   There are two 256-byte ring buffers, one for tx, one for rx.
 *
 *   EP2out is pure tx data. When it appears, the data is copied into the tx
 *   ring and serial transmission is started if it wasn't already running. The
 *   "tx buffer empty" interrupt may kick off another character if the ring
 *   still has data. If the host is tx-blocked because the ring filled up,
 *   it will request a "tx unthrottle" interrupt. If sending a serial character
 *   empties the ring below the desired threshold, we set a bit that will send
 *   up the tx unthrottle message as soon as the rx buffer becomes free.
 *
 *   EP2in (interrupt) is used to send both rx chars and rx status messages
 *   (only "tx unthrottle" at this time) back up to the host. The first byte
 *   of the rx message indicates data (0) or status msg (1). Status messages
 *   are sent before any data.
 *
 *   Incoming serial characters are put into the rx ring by the serial
 *   interrupt, and the EP2in buffer sent if it wasn't already in transit.
 *   When the EP2in buffer returns, the interrupt prompts us to send more
 *   rx chars (or status messages) if they are pending.
 *
 *   Device control happens through "vendor specific" control messages on EP0.
 *   All messages are destined for the "Interface" (with the index always 0,
 *   so that if their two-port device might someday use similar firmware, we
 *   can use index=1 to refer to the second port). The messages defined are:
 *
 *    bRequest = 0 : set baud/bits/parity
 *               1 : unused
 *               2 : reserved for setting HW flow control (CTSRTS)
 *               3 : get/set "modem info" (pin states: DTR, RTS, DCD, RI, etc)
 *               4 : set break (on/off)
 *               5 : reserved for requesting interrupts on pin state change
 *               6 : query buffer room or chars in tx buffer
 *               7 : r