fix booting ram, commit to new size

bootloader.c

@@ -119,7 +119,7 @@ const uint8_t BOOT_SECTOR[0x3e] __attribute__((aligned(2))) = {
 const uint8_t INFO_UF2[70] __attribute__((aligned(2))) = "UF2 Bootloader v0.0.0\nModel: CH32V Generic\nBoard-ID: CH32Vxxx-Generic\n";
 const uint8_t INDEX_HTM[119] __attribute__((aligned(2))) = "<!doctype html>\n<html><body><script>location.replace(\"https://github.com/ArcaneNibble/wch-uf2\")</script></body></html>\n";
 #define THIS_CHIP_FLASH_MAX_SZ_BYTES    (224 * 1024)
-#define BOOTLOADER_RESERVED_SZ_BYTES    (8 * 1024)
+#define BOOTLOADER_RESERVED_SZ_BYTES    (4 * 1024)
 #define THIS_CHIP_RAM_MAX_SZ_BYTES      (20 * 1024)
 #define FAMILY_ID                       0xdeadbeef
 
@@ -864,7 +864,7 @@ __attribute__((naked)) int main(void) {
                             // ram boot
                             R32_RCC_CFGR0 = (R32_RCC_CFGR0 & ~0b11) | 0b00;
                             while ((R32_RCC_CFGR0 & 0b1100) != 0b0000) {}
-                            ((void (*)())0x20000000)();
+                            asm volatile("la t0, 0x20000000\njr t0\n1:\nj 1b\n");
                         } else {
                             // wtf why does this work and the other stuff doesn't?
                             R16_BKP_DATAR10 = 0x4170;

linker.lds

@@ -3,7 +3,7 @@ ENTRY( _start )
 MEMORY
 {
     /* Try to squeeze down to this target size */
-    FLASH (rx) : ORIGIN = 0x00000000, LENGTH = 8K
+    FLASH (rx) : ORIGIN = 0x00000000, LENGTH = 4K
     LOL_NO_RAM (rw) : ORIGIN = 0x400060c0, LENGTH = 0
 }
 

minimal-payload-ram/Makefile

@@ -30,4 +30,4 @@ main.elf: startup.o main.o
 	$(CC) $(CFLAGS) -c -o $@ $<
 
 clean:
-	rm -f *.o *.elf *.map *.dump
+	rm -f *.o *.elf *.map *.dump *.uf2

minimal-payload-ram/main.c

@@ -18,10 +18,10 @@ int main(void) {
     R32_GPIOA_CFGLR = (R32_GPIOA_CFGLR & ~0xf) | (0b0010 << 0);
     while (1) {
         R32_GPIOA_BSHR = 1 << 0;
-        for (int i = 0; i < 500000; i++)
+        for (int i = 0; i < 250000; i++)
             asm volatile("");
         R32_GPIOA_BSHR = 1 << 16;
-        for (int i = 0; i < 500000; i++)
+        for (int i = 0; i < 250000; i++)
             asm volatile("");
     }
 }

minimal-payload/Makefile

@@ -13,7 +13,7 @@ all: main.uf2
 main.elf: startup.o main.o
 
 %.uf2: %.bin
-	~/code/uf2/utils/uf2conv.py -c -f 0xdeadbeef -b 0x08002000 -o $@ $<
+	~/code/uf2/utils/uf2conv.py -c -f 0xdeadbeef -b 0x08001000 -o $@ $<
 
 %.bin: %.elf
 	$(OBJCOPY) -O binary $< $@
@@ -29,4 +29,4 @@ main.elf: startup.o main.o
 	$(CC) $(CFLAGS) -c -o $@ $<
 
 clean:
-	rm -f *.o *.elf *.map *.dump
+	rm -f *.o *.elf *.map *.dump *.uf2

minimal-payload/linker.lds

@@ -7,7 +7,7 @@ MEMORY
 {
     /* CH32V20x_D6 -> 10 KB SRAM */
     /* allow full flash (incl. non-zero-wait) */
-    FLASH (rx) : ORIGIN = 0x00002000, LENGTH = (224K - 8K)
+    FLASH (rx) : ORIGIN = 0x00001000, LENGTH = (224K - 4K)
     RAM (xrw) : ORIGIN = 0x20000000, LENGTH = 10K
 }
 

startup.S

@@ -100,6 +100,5 @@ _enter_bootloader:
     csrw 0xbc0, t0
 
     // Invoke main
-    la t0, main
-    csrw mepc, t0
-    mret
+    // XXX the mepc thing does something really weird
+    j main