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usart_004.c
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1 /*
2 * @brief UART/USART registers and control functions
3 *
4 * @note
5 * Copyright(C) NXP Semiconductors, 2012
6 * All rights reserved.
7 *
8 * @par
9 * Software that is described herein is for illustrative purposes only
10 * which provides customers with programming information regarding the
11 * LPC products. This software is supplied "AS IS" without any warranties of
12 * any kind, and NXP Semiconductors and its licensor disclaim any and
13 * all warranties, express or implied, including all implied warranties of
14 * merchantability, fitness for a particular purpose and non-infringement of
15 * intellectual property rights. NXP Semiconductors assumes no responsibility
16 * or liability for the use of the software, conveys no license or rights under any
17 * patent, copyright, mask work right, or any other intellectual property rights in
18 * or to any products. NXP Semiconductors reserves the right to make changes
19 * in the software without notification. NXP Semiconductors also makes no
20 * representation or warranty that such application will be suitable for the
21 * specified use without further testing or modification.
22 *
23 * @par
24 * Permission to use, copy, modify, and distribute this software and its
25 * documentation is hereby granted, under NXP Semiconductors' and its
26 * licensor's relevant copyrights in the software, without fee, provided that it
27 * is used in conjunction with NXP Semiconductors microcontrollers. This
28 * copyright, permission, and disclaimer notice must appear in all copies of
29 * this code.
30 */
31
32 #include "usart_004.h"
33
34 /*****************************************************************************
35 * Private types/enumerations/variables
36 ****************************************************************************/
37
38 /* Baud-rate pre-scaler multiplier value */
39 #define UART_FDR_MULVAL(n) (((n) << 4) & 0xF0)
40
41 /* Acceptable UART baudrate error */
42 #define UART_ACCEPTED_BAUDRATE_ERROR (3)
43
44 /*****************************************************************************
45 * Public types/enumerations/variables
46 ****************************************************************************/
47
48 /*****************************************************************************
49 * Private functions
50 ****************************************************************************/
51
52 /*****************************************************************************
53 * Public functions
54 ****************************************************************************/
55
56 /* Basic UART initialization */
57 void IP_UART_Init(IP_USART_001_T *pUART)
58 {
59 /* Enable FIFOs by default, reset them */
60 IP_UART_SetupFIFOS(pUART, (UART_FCR_FIFO_EN | UART_FCR_RX_RS | UART_FCR_TX_RS));
61
62 /* Default 8N1, with DLAB disabled */
63 IP_UART_SetMode(pUART, (UART_LCR_WLEN8 | UART_LCR_SBS_1BIT | UART_LCR_PARITY_DIS));
64
65 /* Disable fractional divider */
66 pUART->FDR = 0x10;
67 }
68
69 // FIXME - this function doesn't work correctly and is too big
70 /* Determines and sets best dividers to get a target baud rate */
71 uint32_t IP_UART_SetBaud(IP_USART_001_T *pUART, uint32_t baudrate, uint32_t uClk)
72 {
73 uint32_t actualRate = 0, d, m, bestd, bestm, tmp;
74 uint64_t best_divisor, divisor;
75 uint32_t current_error, best_error;
76 uint32_t recalcbaud;
77
78 /* In the Uart IP block, baud rate is calculated using FDR and DLL-DLM registers
79 * The formula is :
80 * BaudRate= uClk * (mulFracDiv/(mulFracDiv+dividerAddFracDiv) / (16 * (DLL)
81 * It involves floating point calculations. That's the reason the formulae are adjusted with
82 * Multiply and divide method.*/
83 /* The value of mulFracDiv and dividerAddFracDiv should comply to the following expressions:
84 * 0 < mulFracDiv <= 15, 0 <= dividerAddFracDiv <= 15 */
85 best_error = 0xFFFFFFFF;/* Worst case */
86 bestd = 0;
87 bestm = 0;
88 best_divisor = 0;
89 for (m = 1; m <= 15; m++) {
90 for (d = 0; d < m; d++) {
91 divisor = ((uint64_t) uClk << 28) * m / (baudrate * (m + d));
92 current_error = divisor & 0xFFFFFFFF;
93
94 tmp = divisor >> 32;
95
96 /* Adjust error */
97 if (current_error > ((uint32_t) 1 << 31)) {
98 current_error = -current_error;
99 tmp++;
100 }
101
102 if (( tmp < 1) || ( tmp > 65536)) {
103 /* Out of range */
104 continue;
105 }
106
107 if ( current_error < best_error) {
108 best_error = current_error;
109 best_divisor = tmp;
110 bestd = d;
111 bestm = m;
112 if (best_error == 0) {
113 break;
114 }
115 }
116 } /* for (d) */
117
118 if (best_error == 0) {
119 break;
120 }
121 } /* for (m) */
122
123 if (best_divisor == 0) {
124 /* can not find best match */
125 return 0;
126 }
127
128 recalcbaud = (uClk >> 4) * bestm / (best_divisor * (bestm + bestd));
129
130 /* reuse best_error to evaluate baud error */
131 if (baudrate > recalcbaud) {
132 best_error = baudrate - recalcbaud;
133 }
134 else {
135 best_error = recalcbaud - baudrate;
136 }
137
138 best_error = (best_error * 100) / baudrate;
139
140 if (best_error < UART_ACCEPTED_BAUDRATE_ERROR) {
141 IP_UART_EnableDivisorAccess(pUART);
142 // FIXME - this is not how DLL and DLM work - they do not add
143 IP_UART_SetDivisorLatches(pUART, best_divisor, best_divisor);
144 IP_UART_DisableDivisorAccess(pUART);
145
146 /* Set best fractional divider */
147 pUART->FDR = (UART_FDR_MULVAL(bestm) | bestd);
148
149 /* Return actual baud rate */
150 actualRate = recalcbaud;
151 }
152
153 return actualRate;
154 }