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-rw-r--r--driver_fw/serial.c233
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diff --git a/driver_fw/serial.c b/driver_fw/serial.c
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+/* Megumin LED display firmware
+ * Copyright (C) 2018 Sebastian Götte <code@jaseg.net>
+ *
+ * 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 3 of the License, or
+ * (at your option) 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, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "serial.h"
+#include "mac.h"
+
+unsigned int uart_overruns = 0;
+unsigned int invalid_frames = 0;
+
+static union tx_buf_union tx_buf;
+volatile union rx_buf_union rx_buf;
+
+void serial_init() {
+ USART1->CR1 = /* 8-bit -> M1, M0 clear */
+ /* RTOIE clear */
+ (8 << USART_CR1_DEAT_Pos) /* 8 sample cycles/1 bit DE assertion time */
+ | (8 << USART_CR1_DEDT_Pos) /* 8 sample cycles/1 bit DE assertion time */
+ /* OVER8 clear. Use default 16x oversampling */
+ /* CMIF clear */
+ | USART_CR1_MME
+ /* WAKE clear */
+ /* PCE, PS clear */
+ | USART_CR1_RXNEIE /* Enable receive interrupt */
+ /* other interrupts clear */
+ | USART_CR1_TE
+ | USART_CR1_RE;
+ /* Invert TX and DE to accomodate the level shifters */
+ USART1->CR2 = USART_CR2_TXINV;
+ USART1->CR3 = USART_CR3_DEM | USART_CR3_DEP; /* enable RS485 DE (output on RTS) */
+ /* Set divider for 9600 baud rate @48MHz system clock. */
+ int usartdiv = 5000;
+ USART1->BRR = usartdiv;
+
+ /* And... go! */
+ USART1->CR1 |= USART_CR1_UE;
+
+ /* Enable receive interrupt */
+ NVIC_EnableIRQ(USART1_IRQn);
+ NVIC_SetPriority(USART1_IRQn, 1);
+}
+
+void tx_char(uint8_t c) {
+ while (!(USART1->ISR & USART_ISR_TC));
+ USART1->TDR = c;
+}
+
+void send_frame_formatted(uint8_t *buf, int len) {
+ uint8_t *p=buf, *q=buf, *end=buf+len;
+ do {
+ while (*q && q!=end)
+ q++;
+ tx_char(q-p+1);
+ while (*p && p!=end)
+ tx_char(*p++);
+ p++, q++;
+ } while (p < end);
+ tx_char('\0');
+}
+
+void send_status_reply(void) {
+ tx_buf.desc_reply.firmware_version = FIRMWARE_VERSION;
+ tx_buf.desc_reply.hardware_version = HARDWARE_VERSION;
+ tx_buf.desc_reply.pad[0] = tx_buf.desc_reply.pad[1] = 0;
+ tx_buf.desc_reply.uptime_s = sys_time_s;
+ //tx_buf.desc_reply.vcc_mv = adc_vcc_mv;
+ //tx_buf.desc_reply.temp_celsius = adc_temp_celsius;
+ tx_buf.desc_reply.global_brightness = global_brightness;
+ tx_buf.desc_reply.framerate_millifps = frame_duration_us > 0 ? 1000000000 / frame_duration_us : 0;
+ tx_buf.desc_reply.uart_overruns = uart_overruns;
+ tx_buf.desc_reply.invalid_frames = invalid_frames;
+ send_frame_formatted(tx_buf.byte_data, sizeof(tx_buf.desc_reply));
+}
+
+/* This is the higher-level protocol handler for the serial protocol. It gets passed the number of data bytes in this
+ * frame (which may be zero) and returns a pointer to the buffer where the next frame should be stored.
+ */
+volatile uint8_t *packet_received(int len) {
+ static enum {
+ PROT_ADDRESSED = 0,
+ PROT_IGNORE = 2,
+ } protocol_state = PROT_IGNORE;
+ /* Use mac frames as delimiters to synchronize this protocol layer */
+ trigger_comm_led();
+ if (len == 0) { /* Discovery packet */
+ if (sys_time_tick < 100) { /* Only respond during the first 100ms after boot */
+ send_frame_formatted((uint8_t*)&device_mac, sizeof(device_mac));
+ }
+
+ } else if (len == 1) { /* Command packet */
+ if (protocol_state == PROT_ADDRESSED) {
+ switch (rx_buf.byte_data[0]) {
+ case 0x01:
+ send_status_reply();
+ break;
+ }
+ } else {
+ invalid_frames++;
+ trigger_error_led();
+ }
+ protocol_state = PROT_IGNORE;
+
+ } else if (len == 4) { /* Address packet */
+ if (rx_buf.mac_data == device_mac) { /* we are addressed */
+ protocol_state = PROT_ADDRESSED; /* start listening for frame buffer data */
+ } else { /* we are not addressed */
+ protocol_state = PROT_IGNORE; /* ignore packet */
+ }
+
+ } else if (len == sizeof(rx_buf.set_fb_rq)/2) {
+ if (protocol_state == PROT_ADDRESSED) { /* First of two half-framebuffer data frames */
+
+ /* FIXME */
+
+ /* Go to "hang mode" until next zero-length packet. */
+ protocol_state = PROT_IGNORE;
+ }
+
+ } else {
+ /* FIXME An invalid packet has been received. What should we do? */
+ invalid_frames++;
+ trigger_error_led();
+ protocol_state = PROT_IGNORE; /* go into "hang mode" until next zero-length packet */
+ }
+
+ /* By default, return rx_buf.byte_data . This means if an invalid protocol state is reached ("hang mode"), the next
+ * frame is still written to rx_buf. This is not a problem since whatever garbage is written at that point will be
+ * overwritten before the next buffer transfer. */
+ return rx_buf.byte_data;
+}
+
+void USART1_IRQHandler(void) {
+ /* Since a large amount of data will be shoved down this UART interface we need a more reliable and more efficient
+ * way of framing than just waiting between transmissions.
+ *
+ * This code uses "Consistent Overhead Byte Stuffing" (COBS). For details, see its Wikipedia page[0] or the proper
+ * scientific paper[1] published on it. Roughly, it works like this:
+ *
+ * * A frame is at most 254 bytes in length.
+ * * The null byte 0x00 acts as a frame delimiter. There is no null bytes inside frames.
+ * * Every frame starts with an "overhead" byte indicating the number of non-null payload bytes until the next null
+ * byte in the payload, **plus one**. This means this byte can never be zero.
+ * * Every null byte in the payload is replaced by *its* distance to *its* next null byte as above.
+ *
+ * This means, at any point the receiver can efficiently be synchronized on the next frame boundary by simply
+ * waiting for a null byte. After that, only a simple state machine is necessary to strip the overhead byte and a
+ * counter to then count skip intervals.
+ *
+ * Here is Wikipedia's table of example values:
+ *
+ * Unencoded data Encoded with COBS
+ * 00 01 01 00
+ * 00 00 01 01 01 00
+ * 11 22 00 33 03 11 22 02 33 00
+ * 11 22 33 44 05 11 22 33 44 00
+ * 11 00 00 00 02 11 01 01 01 00
+ * 01 02 ...FE FF 01 02 ...FE 00
+ *
+ * [0] https://en.wikipedia.org/wiki/Consistent_Overhead_Byte_Stuffing
+ * [1] Cheshire, Stuart; Baker, Mary (1999). "Consistent Overhead Byte Stuffing"
+ * IEEE/ACM Transactions on Networking. doi:10.1109/90.769765
+ * http://www.stuartcheshire.org/papers/COBSforToN.pdf
+ */
+
+ /* This pointer stores where we write data. The higher-level protocol logic decides on a frame-by-frame-basis where
+ * the next frame's data will be stored. */
+ static volatile uint8_t *writep = rx_buf.byte_data;
+ /* Index inside the current frame payload */
+ static int rxpos = 0;
+ /* COBS state machine. This implementation might be a little too complicated, but it works well enough and I find it
+ * reasonably easy to understand. */
+ static enum {
+ COBS_WAIT_SYNC = 0, /* Synchronize with frame */
+ COBS_WAIT_START = 1, /* Await overhead byte */
+ COBS_RUNNING = 2 /* Process payload */
+ } cobs_state = 0;
+ /* COBS skip counter. During payload processing this contains the remaining non-null payload bytes */
+ static int cobs_count = 0;
+
+ if (USART1->ISR & USART_ISR_ORE) { /* Overrun handling */
+ uart_overruns++;
+ trigger_error_led();
+ /* Reset and re-synchronize. Retry next frame. */
+ rxpos = 0;
+ cobs_state = COBS_WAIT_SYNC;
+ /* Clear interrupt flag */
+ USART1->ICR = USART_ICR_ORECF;
+
+ } else { /* Data received */
+ uint8_t data = USART1->RDR; /* This automatically acknowledges the IRQ */
+
+ if (data == 0x00) { /* End-of-packet */
+ /* Process higher protocol layers on this packet. */
+ writep = packet_received(rxpos);
+
+ /* Reset for next packet. */
+ cobs_state = COBS_WAIT_START;
+ rxpos = 0;
+
+ } else { /* non-null byte */
+ if (cobs_state == COBS_WAIT_SYNC) { /* Wait for null byte */
+ /* ignore data */
+
+ } else if (cobs_state == COBS_WAIT_START) { /* Overhead byte */
+ cobs_count = data;
+ cobs_state = COBS_RUNNING;
+
+ } else { /* Payload byte */
+ if (--cobs_count == 0) { /* Skip byte */
+ cobs_count = data;
+ data = 0;
+ }
+
+ /* Write processed payload byte to current receive buffer */
+ writep[rxpos++] = data;
+ }
+ }
+ }
+}
+