USART enhanced: add additional data bits and parity support
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/* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*
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*/
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/** library for enhanced USART communication (code)
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* @file usart_enhanced.c
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* @author King Kévin <kingkevin@cuvoodoo.info>
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* @date 2018
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* @details the USART peripherals only support 8 or 9-bit word and even or odd parity (included in the data bits). The library adds support for 5 to 8-bit words, none/even/odd/mark/space parity (on top of the data bits)
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* @note since parity is handled in software, the parity error (PE) flag is unused and should be replaced by the value return by usart_enhanced_parity_error
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* @remark 9-bit raw communication is not supported since this is not common and can be done without this library
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*/
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/* standard libraries */
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#include <stdint.h> // standard integer types
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/* STM32 (including CM3) libraries */
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#include <libopencm3/stm32/usart.h> // USART utilities
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/* own libraries */
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#include "usart_enhanced.h" // utilities for USART enhancements
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/** number of available USART peripherals */
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#define USART_PERIPHERALS_NB 3
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/** configured enhanced USART word size */
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static uint8_t usart_enhanced_databits[USART_PERIPHERALS_NB];
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/** configured enhanced USART parity */
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static enum usart_enhanced_parity_t usart_enhanced_parity[USART_PERIPHERALS_NB];
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/** last enhanced USART parity error status */
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static bool usart_enhanced_parity_errors[USART_PERIPHERALS_NB];
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/** know if there is an even number of 1's in a integer
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* @remark a look-up is a lot faster than making the calculation and doesn't does a lot of (flash) space
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*/
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static const bool even_parity_lut[256] = { true, false, false, true, false, true, true, false, false, true, true, false, true, false, false, true, false, true, true, false, true, false, false, true, true, false, false, true, false, true, true, false, false, true, true, false, true, false, false, true, true, false, false, true, false, true, true, false, true, false, false, true, false, true, true, false, false, true, true, false, true, false, false, true, false, true, true, false, true, false, false, true, true, false, false, true, false, true, true, false, true, false, false, true, false, true, true, false, false, true, true, false, true, false, false, true, true, false, false, true, false, true, true, false, false, true, true, false, true, false, false, true, false, true, true, false, true, false, false, true, true, false, false, true, false, true, true, false, false, true, true, false, true, false, false, true, true, false, false, true, false, true, true, false, true, false, false, true, false, true, true, false, false, true, true, false, true, false, false, true, true, false, false, true, false, true, true, false, false, true, true, false, true, false, false, true, false, true, true, false, true, false, false, true, true, false, false, true, false, true, true, false, true, false, false, true, false, true, true, false, false, true, true, false, true, false, false, true, false, true, true, false, true, false, false, true, true, false, false, true, false, true, true, false, false, true, true, false, true, false, false, true, true, false, false, true, false, true, true, false, true, false, false, true, false, true, true, false, false, true, true, false, true, false, false, true, };
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/** get index of corresponding enhanced USART configurations
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* @param[in] usart USART peripheral base address
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* @return index used for the individual USART configurations
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* @note the returned value is valid only is less than USART_PERIPHERALS_NB
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*/
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static uint8_t usart_enhanced_id(uint32_t usart)
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{
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uint8_t to_return = USART_PERIPHERALS_NB;
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switch (usart) {
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case USART1:
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to_return = 0;
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break;
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case USART2:
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to_return = 1;
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break;
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case USART3:
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to_return = 2;
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break;
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default:
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to_return = USART_PERIPHERALS_NB;
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break;
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}
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return to_return;
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}
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bool usart_enhanced_config(uint32_t usart, uint8_t databits, enum usart_enhanced_parity_t parity)
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{
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/* sanity check */
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uint8_t id = usart_enhanced_id(usart);
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if (id>=USART_PERIPHERALS_NB) {
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return false;
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}
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if (databits<5 || databits>8) {
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return false;
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}
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if (parity>USART_ENHANCED_PARITY_SPACE) {
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return false;
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}
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// save configuration for later use
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usart_enhanced_databits[id] = databits;
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usart_enhanced_parity[id] = parity;
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// configure USART peripheral
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if (8==databits && USART_ENHANCED_PARITY_NONE!=parity) { // the parity bit is additional to the data bits
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usart_set_databits(usart, 9);
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} else {
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usart_set_databits(usart, 8);
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}
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usart_set_parity(usart, USART_PARITY_NONE); // set no parity since we will take care of it ourselves
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// we could also lower the number of stop bits when less than 8 bits are used, for higher throughput, but this is not a good idea since most UART transceiver parse 8 bits even is less is used
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return true;
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}
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void usart_enhanced_send(uint32_t usart, uint8_t data)
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{
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/* sanity check */
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uint8_t id = usart_enhanced_id(usart);
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if (id>=USART_PERIPHERALS_NB) {
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return;
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}
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data &= ~(0xff<<usart_enhanced_databits[id]); // only keep the data bits
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uint16_t output = data; // put value in output buffer
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switch (usart_enhanced_parity[id]) {
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case USART_ENHANCED_PARITY_NONE: // a mark is also decoded as idle/stop
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case USART_ENHANCED_PARITY_MARK:
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output |= (1<<usart_enhanced_databits[id]); // add idle state
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break;
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case USART_ENHANCED_PARITY_EVEN:
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if (!even_parity_lut[data]) {
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output |= (1<<usart_enhanced_databits[id]);
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}
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// no need to clear a bit if the parity is even
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break;
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case USART_ENHANCED_PARITY_ODD:
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if (even_parity_lut[data]) {
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output |= (1<<usart_enhanced_databits[id]);
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}
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// no need to clear a bit if the parity is odd
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break;
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case USART_ENHANCED_PARITY_SPACE:
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// no need to clear the bit
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break;
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}
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output |= (0xffff<<(usart_enhanced_databits[id]+1)); // set additional bits to idle (high)
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usart_send(usart, output); // transmit character
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}
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uint8_t usart_enhanced_recv(uint32_t usart)
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{
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/* sanity check */
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uint8_t id = usart_enhanced_id(usart);
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if (id>=USART_PERIPHERALS_NB) {
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return 0xff;
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}
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uint16_t input = usart_recv(usart); // read received character (also clears the error flags)
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input &= ~(0xffff<<(usart_enhanced_databits[id]+1)); // only keep the data bits + parity bit
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// check the parity
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uint16_t parity = input&(1<<usart_enhanced_databits[id]); // only keep the parity bit
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usart_enhanced_parity_errors[id] = false;
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switch (usart_enhanced_parity[id]) {
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case USART_ENHANCED_PARITY_NONE:
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usart_enhanced_parity_errors[id] = false;
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break;
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case USART_ENHANCED_PARITY_EVEN:
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if (parity) {
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usart_enhanced_parity_errors[id] = !even_parity_lut[input&0xff];
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} else {
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usart_enhanced_parity_errors[id] = even_parity_lut[input&0xff];
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}
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break;
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case USART_ENHANCED_PARITY_ODD:
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if (parity) {
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usart_enhanced_parity_errors[id] = even_parity_lut[input&0xff];
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} else {
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usart_enhanced_parity_errors[id] = !even_parity_lut[input&0xff];
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}
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break;
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case USART_ENHANCED_PARITY_MARK:
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usart_enhanced_parity_errors[id] = !parity;
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break;
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case USART_ENHANCED_PARITY_SPACE:
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usart_enhanced_parity_errors[id] = parity;
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break;
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}
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input &= ~(0xffff<<(usart_enhanced_databits[id])); // only keep the data bits
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return input;
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}
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bool usart_enhanced_parity_error(uint32_t usart)
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{
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/* sanity check */
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uint8_t id = usart_enhanced_id(usart);
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if (id>=USART_PERIPHERALS_NB) {
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return false;
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}
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return usart_enhanced_parity_errors[id];
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}
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@ -0,0 +1,71 @@
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/* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*
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*/
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/** library for enhanced USART communication (API)
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* @file usart_enhanced.h
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* @author King Kévin <kingkevin@cuvoodoo.info>
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* @date 2018
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* @details the USART peripherals only support 8 or 9-bit word and even or odd parity (included in the data bits). The library adds support for 5 to 8-bit words, none/even/odd/mark/space parity (on top of the data bits)
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* @note since parity is handled in software, the parity error (PE) flag is unused and should be replaced by the value return by usart_enhanced_parity_error
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* @remark 9-bit raw communication is not supported since this is not common and can be done without this library
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*/
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#pragma once
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/** enhanced USART setting for the additional parity bit*/
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enum usart_enhanced_parity_t {
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/** no parity */
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USART_ENHANCED_PARITY_NONE,
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/** even parity
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* @note the number of 1's is even
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*/
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USART_ENHANCED_PARITY_EVEN,
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/** odd parity
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* @note the number of 1's is odd
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*/
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USART_ENHANCED_PARITY_ODD,
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/** mark parity
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* @note the parity bit is 1
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*/
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USART_ENHANCED_PARITY_MARK,
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/** space parity
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* @note the parity bit is 0
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*/
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USART_ENHANCED_PARITY_SPACE,
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};
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/** configure enhanced USART
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* @param[in] usart USART peripheral base address
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* @param[in] databits word size in bits (5 to 8)
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* @param[in] parity additional parity bit
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* @return if the input settings are valid and the configuration is successful
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*/
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bool usart_enhanced_config(uint32_t usart, uint8_t databits, enum usart_enhanced_parity_t parity);
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/** send data over the enhanced USART using the configuration
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* @param[in] usart USART peripheral base address
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* @param[in] data data to be sent
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* @note uses usart_send
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*/
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void usart_enhanced_send(uint32_t usart, uint8_t data);
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/** receive data over the enhanced USART using the configuration
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* @param[in] usart USART peripheral base address
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* @return data received
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* @note uses usart_recv
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*/
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uint8_t usart_enhanced_recv(uint32_t usart);
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/** get the parity status of the received data
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* @param[in] usart USART peripheral base address
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* @return if there is a parity error
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* @note the check only applies to the last data retrieved using usart_enhanced_recv
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*/
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bool usart_enhanced_parity_error(uint32_t usart);
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