1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
|
/*
* Copyright (C) 2025 Michael Brown <mbrown@fensystems.co.uk>.
*
* 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 any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
* 02110-1301, USA.
*
* You can also choose to distribute this program under the terms of
* the Unmodified Binary Distribution Licence (as given in the file
* COPYING.UBDL), provided that you have satisfied its requirements.
*/
FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
/** @file
*
* 16550-compatible UART
*
*/
#include <unistd.h>
#include <errno.h>
#include <ipxe/uart.h>
#include <ipxe/ns16550.h>
/** Timeout for transmit holding register to become empty */
#define NS16550_THRE_TIMEOUT_MS 100
/** Timeout for transmitter to become empty */
#define NS16550_TEMT_TIMEOUT_MS 1000
/**
* Transmit data
*
* @v uart UART
* @v data Data
*/
static void ns16550_transmit ( struct uart *uart, uint8_t data ) {
struct ns16550_uart *ns16550 = uart->priv;
unsigned int i;
uint8_t lsr;
/* Wait for transmitter holding register to become empty */
for ( i = 0 ; i < NS16550_THRE_TIMEOUT_MS ; i++ ) {
lsr = ns16550_read ( ns16550, NS16550_LSR );
if ( lsr & NS16550_LSR_THRE )
break;
mdelay ( 1 );
}
/* Transmit data (even if we timed out) */
ns16550_write ( ns16550, NS16550_THR, data );
}
/**
* Check if data is ready
*
* @v uart UART
* @ret ready Data is ready
*/
static int ns16550_data_ready ( struct uart *uart ) {
struct ns16550_uart *ns16550 = uart->priv;
uint8_t lsr;
/* Check for receive data ready */
lsr = ns16550_read ( ns16550, NS16550_LSR );
return ( lsr & NS16550_LSR_DR );
}
/**
* Receive data
*
* @v uart UART
* @ret data Data
*/
static uint8_t ns16550_receive ( struct uart *uart ) {
struct ns16550_uart *ns16550 = uart->priv;
uint8_t rbr;
/* Receive byte */
rbr = ns16550_read ( ns16550, NS16550_RBR );
return rbr;
}
/**
* Flush transmitted data
*
* @v uart UART
*/
static void ns16550_flush ( struct uart *uart ) {
struct ns16550_uart *ns16550 = uart->priv;
unsigned int i;
uint8_t lsr;
/* Wait for transmitter to become empty */
for ( i = 0 ; i < NS16550_TEMT_TIMEOUT_MS ; i++ ) {
lsr = ns16550_read ( ns16550, NS16550_LSR );
if ( lsr & NS16550_LSR_TEMT )
break;
}
}
/**
* Initialise UART
*
* @v uart UART
* @ret rc Return status code
*/
static int ns16550_init ( struct uart *uart ) {
struct ns16550_uart *ns16550 = uart->priv;
uint8_t dlm;
uint8_t dll;
/* Fail if UART scratch register seems not to be present */
ns16550_write ( ns16550, NS16550_SCR, 0x18 );
if ( ns16550_read ( ns16550, NS16550_SCR ) != 0x18 )
return -ENODEV;
ns16550_write ( ns16550, NS16550_SCR, 0xae );
if ( ns16550_read ( ns16550, NS16550_SCR ) != 0xae )
return -ENODEV;
/* Wait for UART to become idle before modifying LCR */
ns16550_flush ( uart );
/* Configure divisor and line control register, if applicable */
ns16550_write ( ns16550, NS16550_LCR,
( NS16550_LCR_8N1 | NS16550_LCR_DLAB ) );
if ( uart->baud ) {
ns16550->divisor = ( ( ns16550->clock / uart->baud ) /
NS16550_CLK_BIT );
dlm = ( ( ns16550->divisor >> 8 ) & 0xff );
dll = ( ( ns16550->divisor >> 0 ) & 0xff );
ns16550_write ( ns16550, NS16550_DLM, dlm );
ns16550_write ( ns16550, NS16550_DLL, dll );
} else {
dlm = ns16550_read ( ns16550, NS16550_DLM );
dll = ns16550_read ( ns16550, NS16550_DLL );
ns16550->divisor = ( ( dlm << 8 ) | dll );
}
ns16550_write ( ns16550, NS16550_LCR, NS16550_LCR_8N1 );
/* Disable interrupts */
ns16550_write ( ns16550, NS16550_IER, 0 );
/* Enable FIFOs */
ns16550_write ( ns16550, NS16550_FCR, NS16550_FCR_FE );
/* Assert DTR and RTS */
ns16550_write ( ns16550, NS16550_MCR,
( NS16550_MCR_DTR | NS16550_MCR_RTS ) );
/* Flush any stale received data */
while ( ns16550_data_ready ( uart ) )
ns16550_receive ( uart );
return 0;
}
/** 16550 UART operations */
struct uart_operations ns16550_operations = {
.transmit = ns16550_transmit,
.data_ready = ns16550_data_ready,
.receive = ns16550_receive,
.init = ns16550_init,
.flush = ns16550_flush,
};
|
