From d46862a5bd2319c595b11427f781201ca063d194 Mon Sep 17 00:00:00 2001
From: Thomas Albers Raviola <thomas@thomaslabs.org>
Date: Tue, 3 Dec 2024 21:45:47 +0100
Subject: Add bootloader
---
boot/bootloader.c | 376 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 376 insertions(+)
create mode 100644 boot/bootloader.c
(limited to 'boot/bootloader.c')
diff --git a/boot/bootloader.c b/boot/bootloader.c
new file mode 100644
index 0000000..042414b
--- /dev/null
+++ b/boot/bootloader.c
@@ -0,0 +1,376 @@
+#include <hardware.h>
+#include <zeta.h>
+#include <fifo.h>
+
+#include <assert.h>
+#include <stddef.h>
+#include <string.h>
+
+#ifdef __GNUC__
+#define PACKED __attribute__((packed))
+#else
+#define PACKED
+#endif
+
+u16
+crc16(const void *buf, size_t len);
+
+enum header_type {
+ CMD_PING,
+ CMD_INFO,
+ CMD_BOOT,
+ CMD_READ,
+ CMD_WRITE,
+ CMD_IO_READ,
+ CMD_IO_WRITE,
+ CMD_ECHO
+};
+
+struct header {
+ u8 type;
+ u8 bank;
+ u16 address;
+ u16 length;
+ u16 checksum;
+} PACKED;
+
+// static_assert(sizeof(struct header) == 8, "struct header is not PACKED");
+
+enum error {
+ ERR_TIMEOUT = -1
+};
+
+#define MAX_PACKET_SIZE 256
+#define TIMEOUT_MS 500
+#define MAX_ATTEMPTS 3
+#define MAX_TRANS_ATTEMPTS 5
+
+u16
+crc16(const void *buf, size_t len);
+
+volatile struct fifo rx_fifo = {0, 0, {0}};
+
+enum ack {
+ ACK = 0x00,
+ NACK = 0xFF
+};
+
+void
+rx_isr(void) __critical __interrupt(0)
+{
+ fifo_push(&rx_fifo, sio_a_data);
+}
+
+static volatile uint32_t millis = 0;
+
+void
+ctc1_isr(void) __critical __interrupt(1)
+{
+ millis += 5;
+}
+
+uint32_t
+clock(void)
+{
+ volatile uint32_t ret;
+ DI;
+ ret = millis;
+ EI;
+ return ret;
+}
+
+void
+putbyte(unsigned char b)
+{
+ unsigned char ctrl = 0;
+
+ sio_a_data = b;
+
+ while (!(ctrl & 0x04)) {
+ sio_a_ctrl = 0;
+ ctrl = sio_a_ctrl;
+ }
+}
+
+static volatile int32_t errno = 0;
+
+u8
+getbyte(void)
+{
+ u8 b;
+ uint32_t ms = clock();
+ errno = 0;
+ while (fifo_empty(&rx_fifo)) {
+ if (clock() - ms > TIMEOUT_MS) {
+ errno = ERR_TIMEOUT;
+ return 0;
+ }
+ }
+ DI;
+ b = fifo_pop(&rx_fifo);
+ EI;
+ return b;
+}
+
+void
+flush(void)
+{
+ DI;
+ fifo_clear(&rx_fifo);
+ EI;
+}
+
+
+// Hamming(7,4) encoding
+u8
+encode(u8 x)
+{
+ u8 y = 0;
+ const u8 c[4] = {0x61, 0x52, 0x34, 0x78};
+
+ for (u8 i = 0; i < 4; ++i)
+ y ^= ((x >> i) & 1) ? c[i] : 0;
+
+ return y;
+}
+
+// Hamming(7,4) decoding
+u8
+decode(u8 x)
+{
+ u8 p = 0;
+ const u8 r[7] = {6, 5, 3, 7, 1, 2, 4};
+
+ for (int i = 0; i < 7; ++i)
+ p ^= ((x >> i) & 1) ? r[i] : 0;
+
+ // Assume simple error, attempt correction
+ if (p) {
+ size_t i = 0;
+
+ for (i = 0; i < LENGTH(r); ++i) {
+ if (r[i] == x)
+ break;
+ }
+
+ x ^= (1 << i);
+ }
+
+ return x & 0x0F;
+}
+
+
+int
+read(void *buf, size_t count)
+{
+ u8 b;
+ u8 *p = buf;
+
+ for (int n = 0; n < count; ++n) {
+ b = decode(getbyte());
+ if (errno)
+ return errno;
+
+ b |= (decode(getbyte()) << 4);
+ if (errno)
+ return errno;
+
+ p[n] = b;
+ }
+
+ return 0;
+}
+
+int
+write(const void *buf, size_t count)
+{
+ const u8 *p = buf;
+
+ for (size_t i = 0; i < count; ++i) {
+ putbyte(encode(p[i] & 0x0F));
+ putbyte(encode((p[i] >> 4) & 0x0F));
+ }
+
+ return 0;
+}
+
+int
+read_header(struct header *header)
+{
+ int err;
+ u8 ack;
+ u16 checksum;
+
+ while (1) {
+ if ((err = read(header, sizeof(*header))))
+ return err;
+
+ checksum = header->checksum;
+ header->checksum = 0;
+
+ if (checksum == crc16(header, sizeof(*header))) {
+ header->checksum = checksum;
+ ack = ACK;
+ write(&ack, sizeof(ack));
+ return 0;
+ } else {
+ ack = NACK;
+ write(&ack, sizeof(ack));
+ }
+ }
+}
+
+int
+read_buf(size_t len, void *buf)
+{
+ int err;
+ u8 ack;
+ u16 checksum;
+
+ for (int i = 0; i < MAX_TRANS_ATTEMPTS; ++i) {
+ // TODO: reduce code?
+ if ((err = read(&checksum, sizeof(checksum)))
+ || (err = read(buf, len)))
+ break;
+
+ if (checksum == crc16(buf, len)) {
+ ack = ACK;
+ write(&ack, sizeof(ack));
+ return 0;
+ } else {
+ ack = NACK;
+ write(&ack, sizeof(ack));
+ }
+ }
+
+ return -1;
+}
+
+int
+write_buf(size_t len, const void *buf)
+{
+ int err;
+ u8 ack = NACK;
+ u16 checksum = crc16(buf, len);
+
+ for (int i = 0; i < MAX_TRANS_ATTEMPTS; ++i){
+ write(&checksum, sizeof(checksum));
+ write(buf, len);
+
+ // If TIMEOUT sending just give up
+ if ((err = read(&ack, sizeof(ack))))
+ return err;
+
+ if (ack == ACK)
+ return 0;
+ }
+
+ return -1;
+}
+
+// TODO: Restart after timeouts
+void
+loop(void)
+{
+ struct header header;
+ u8 buf[MAX_PACKET_SIZE];
+
+ while (1) {
+ if (read_header(&header)) {
+ flush();
+ continue;
+ }
+
+ switch (header.type) {
+ case CMD_BOOT:
+ ((void (*)(void))header.address)();
+ break;
+
+ case CMD_READ:
+ write_buf(header.length, (const void *)header.address);
+ break;
+
+ case CMD_WRITE:
+ if (!read_buf(header.length, buf))
+ memcpy((void *)header.address, buf, header.length);
+ break;
+
+ case CMD_ECHO:
+ if (!read_buf(header.length, buf))
+ write_buf(header.length, buf);
+ break;
+
+ default:
+ break;
+ }
+
+ flush();
+ }
+}
+
+static inline void
+init_ctc(void)
+{
+ ctc_channel_0 = CTC_CTRL(0);
+
+ /* 200Hz clock */
+ ctc_channel_1 = CTC_CTRL(CTC_INT_BIT | CTC_PRESCALER_BIT
+ | CTC_TIME_CONST_BIT | CTC_RST_BIT);
+ ctc_channel_1 = 0;
+
+ ctc_channel_2 = CTC_CTRL(0);
+ ctc_channel_3 = CTC_CTRL(0);
+
+ // Interrupt table for CTC
+ // Final address is (Ireg << 8) | ctc_isr_ptr | {00/01/10/11} | 0
+ ctc_channel_0 = CTC_INT_VEC(0x10);
+}
+
+static inline void
+init_pio(void)
+{
+ // Disable PIO interrupts
+ port_a_ctrl = PIO_INT_CTRL(0);
+ port_b_ctrl = PIO_INT_CTRL(0);
+}
+
+static inline void
+init_sio(void)
+{
+ static const u8 sio_a_cfg[] = {
+ 0b00011000, // Reset channel
+ 4 , // wr4
+ 0b01000100, // X16 clock (115200), one stop bit, no parity
+ 1 , // wr1
+ SIO_RX_INT_MD0 | SIO_RX_INT_MD1, // interrupt on every Rx, no wait function
+ 3 , // wr3
+ 0b11000001, // enable Rx - 8 bit char
+ 5 , // wr5
+ 0b01101000 // enable Tx - 8 bit char
+ };
+
+ static const u8 sio_b_cfg[] = {
+ 0b00011000, // Reset channel
+ 2 , // load interrupt vector
+ 0x1C // int_table_rx
+ };
+
+ for (u8 i = 0; i < LENGTH(sio_a_cfg); ++i)
+ sio_a_ctrl = sio_a_cfg[i];
+
+ for (u8 i = 0; i < LENGTH(sio_b_cfg); ++i)
+ sio_b_ctrl = sio_b_cfg[i];
+}
+
+void
+main(void)
+{
+ init_ctc();
+ init_pio();
+ init_sio();
+
+ IM(2);
+ EI;
+
+ loop();
+}
--
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