From 83aef192e447c800cba6f4dbde8a450a4f8581a5 Mon Sep 17 00:00:00 2001
From: Jacques Comeaux <jacquesrcomeaux@protonmail.com>
Date: Mon, 1 Jul 2024 12:16:02 -0500
Subject: Use in-house CRC32 computation for boot sector

---
 octedit/.gitignore      |  1 +
 octedit/Makefile        | 13 ++++++++-----
 octedit/crc.s           |  6 ------
 octedit/crc32.c         | 22 ++++++++++++++++++++++
 octedit/pico_persist.ld |  5 ++---
 5 files changed, 33 insertions(+), 14 deletions(-)
 create mode 100644 octedit/.gitignore
 delete mode 100644 octedit/crc.s
 create mode 100644 octedit/crc32.c

(limited to 'octedit')

diff --git a/octedit/.gitignore b/octedit/.gitignore
new file mode 100644
index 0000000..2d5bda1
--- /dev/null
+++ b/octedit/.gitignore
@@ -0,0 +1 @@
+crc32
diff --git a/octedit/Makefile b/octedit/Makefile
index 74ce9d4..cc3773d 100644
--- a/octedit/Makefile
+++ b/octedit/Makefile
@@ -15,20 +15,23 @@ octedit.uf2: octedit.bin
 	printf %220s | tr " " "\0" >> octedit.uf2  # 0 padding
 	echo -ne "\x30\x6F\xB1\x0A" >> octedit.uf2 # Magic end
 
-octedit.bin: octedit.elf
+octedit.bin: octedit.elf crc32
 	arm-none-eabi-objcopy -O binary octedit.elf octedit.bin
+	./crc32 < octedit.bin >> octedit.bin
 
-objects = setup.o octedit.o uart.o crc.o
+crc32: crc32.c
+	gcc crc32.c -o crc32
 
-octedit.elf: $(objects)
+objects = setup.o octedit.o uart.o
+
+octedit.elf: $(objects) pico_persist.ld
 	arm-none-eabi-ld -T pico_persist.ld -o octedit.elf $(objects)
-	./checksum_pico_elf.py octedit.elf
 
 $(objects): %.o: %.s
 	arm-none-eabi-as -o $@ $<
 
 clean:
-	rm octedit.elf octedit.bin octedit.uf2 *.o
+	rm octedit.elf octedit.bin octedit.uf2 *.o crc32
 
 flash: octedit.uf2
 	[ -h /dev/disk/by-label/RPI-RP2 ] || sleep 3s
diff --git a/octedit/crc.s b/octedit/crc.s
deleted file mode 100644
index 8019c6d..0000000
--- a/octedit/crc.s
+++ /dev/null
@@ -1,6 +0,0 @@
-.syntax unified
-.cpu cortex-m0plus
-.thumb
-
-.section .stage_2_crc
-.word 0x00000000
diff --git a/octedit/crc32.c b/octedit/crc32.c
new file mode 100644
index 0000000..175ab50
--- /dev/null
+++ b/octedit/crc32.c
@@ -0,0 +1,22 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <stdint.h>
+
+#define DATA_LEN 252
+#define DIVISOR 0x04C11DB7
+
+int main() {
+  uint8_t data[DATA_LEN];
+  read(STDIN_FILENO, data, DATA_LEN);
+  uint32_t crc = 0xFFFFFFFF;
+  for (size_t i = 0; i < DATA_LEN; i++) {
+    crc ^= data[i] << 24;
+    for (uint8_t j = 0; j < 8; j++) {
+      uint8_t nskip = crc >> 31;
+      crc <<= 1;
+      if (nskip) crc ^= DIVISOR;
+    }
+  }
+  write(STDOUT_FILENO, (uint8_t *) &crc, 4);
+  return 0;
+}
diff --git a/octedit/pico_persist.ld b/octedit/pico_persist.ld
index fd9cf67..14caad7 100644
--- a/octedit/pico_persist.ld
+++ b/octedit/pico_persist.ld
@@ -1,6 +1,6 @@
 MEMORY {
   FLASH(rx) : ORIGIN = 0x10000000, LENGTH = 2M
-  SRAM(rx) : ORIGIN = 0x20041f00, LENGTH = 256
+  SRAM(rx) : ORIGIN = 0x20041f00, LENGTH = 252
 }
 
 SECTIONS {
@@ -8,7 +8,6 @@ SECTIONS {
     setup.o(.text);
     octedit.o(.text);
     uart.o(.text);
-    . = 252;
-    *(.stage_2_crc);
+    . = LENGTH(SRAM);
   } >SRAM AT>FLASH
 }
-- 
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