1 /*
2 * Copyright (C) 2014 Michael Brown <mbrown@fensystems.co.uk>.
3 *
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License as
6 * published by the Free Software Foundation; either version 2 of the
7 * License, or any later version.
8 *
9 * This program is distributed in the hope that it will be useful, but
10 * WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 * General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
17 * 02110-1301, USA.
18 *
19 * You can also choose to distribute this program under the terms of
20 * the Unmodified Binary Distribution Licence (as given in the file
21 * COPYING.UBDL), provided that you have satisfied its requirements.
22 */
23
24 FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
25
26 /** @file
27 *
28 * 16550-compatible UART
29 *
30 */
31
32 #include <unistd.h>
33 #include <errno.h>
34 #include <ipxe/uart.h>
35
36 /** Timeout for transmit holding register to become empty */
37 #define UART_THRE_TIMEOUT_MS 100
38
39 /** Timeout for transmitter to become empty */
40 #define UART_TEMT_TIMEOUT_MS 1000
41
42 /**
43 * Transmit data
44 *
45 * @v uart UART
46 * @v data Data
47 */
uart_transmit(struct uart * uart,uint8_t data)48 void uart_transmit ( struct uart *uart, uint8_t data ) {
49 unsigned int i;
50 uint8_t lsr;
51
52 /* Wait for transmitter holding register to become empty */
53 for ( i = 0 ; i < UART_THRE_TIMEOUT_MS ; i++ ) {
54 lsr = uart_read ( uart, UART_LSR );
55 if ( lsr & UART_LSR_THRE )
56 break;
57 mdelay ( 1 );
58 }
59
60 /* Transmit data (even if we timed out) */
61 uart_write ( uart, UART_THR, data );
62 }
63
64 /**
65 * Flush data
66 *
67 * @v uart UART
68 */
uart_flush(struct uart * uart)69 void uart_flush ( struct uart *uart ) {
70 unsigned int i;
71 uint8_t lsr;
72
73 /* Wait for transmitter and receiver to become empty */
74 for ( i = 0 ; i < UART_TEMT_TIMEOUT_MS ; i++ ) {
75 uart_read ( uart, UART_RBR );
76 lsr = uart_read ( uart, UART_LSR );
77 if ( ( lsr & UART_LSR_TEMT ) && ! ( lsr & UART_LSR_DR ) )
78 break;
79 }
80 }
81
82 /**
83 * Check for existence of UART
84 *
85 * @v uart UART
86 * @ret rc Return status code
87 */
uart_exists(struct uart * uart)88 int uart_exists ( struct uart *uart ) {
89
90 /* Fail if no UART port is defined */
91 if ( ! uart->base )
92 return -ENODEV;
93
94 /* Fail if UART scratch register seems not to be present */
95 uart_write ( uart, UART_SCR, 0x18 );
96 if ( uart_read ( uart, UART_SCR ) != 0x18 )
97 return -ENODEV;
98 uart_write ( uart, UART_SCR, 0xae );
99 if ( uart_read ( uart, UART_SCR ) != 0xae )
100 return -ENODEV;
101
102 return 0;
103 }
104
105 /**
106 * Initialise UART
107 *
108 * @v uart UART
109 * @v baud Baud rate, or zero to leave unchanged
110 * @v lcr Line control register value, or zero to leave unchanged
111 * @ret rc Return status code
112 */
uart_init(struct uart * uart,unsigned int baud,uint8_t lcr)113 int uart_init ( struct uart *uart, unsigned int baud, uint8_t lcr ) {
114 uint8_t dlm;
115 uint8_t dll;
116 int rc;
117
118 /* Check for existence of UART */
119 if ( ( rc = uart_exists ( uart ) ) != 0 )
120 return rc;
121
122 /* Configure divisor and line control register, if applicable */
123 if ( ! lcr )
124 lcr = uart_read ( uart, UART_LCR );
125 uart->lcr = lcr;
126 uart_write ( uart, UART_LCR, ( lcr | UART_LCR_DLAB ) );
127 if ( baud ) {
128 uart->divisor = ( UART_MAX_BAUD / baud );
129 dlm = ( ( uart->divisor >> 8 ) & 0xff );
130 dll = ( ( uart->divisor >> 0 ) & 0xff );
131 uart_write ( uart, UART_DLM, dlm );
132 uart_write ( uart, UART_DLL, dll );
133 } else {
134 dlm = uart_read ( uart, UART_DLM );
135 dll = uart_read ( uart, UART_DLL );
136 uart->divisor = ( ( dlm << 8 ) | dll );
137 }
138 uart_write ( uart, UART_LCR, ( lcr & ~UART_LCR_DLAB ) );
139
140 /* Disable interrupts */
141 uart_write ( uart, UART_IER, 0 );
142
143 /* Enable FIFOs */
144 uart_write ( uart, UART_FCR, UART_FCR_FE );
145
146 /* Assert DTR and RTS */
147 uart_write ( uart, UART_MCR, ( UART_MCR_DTR | UART_MCR_RTS ) );
148
149 /* Flush any stale data */
150 uart_flush ( uart );
151
152 return 0;
153 }
154