Add stage 1 editor and update README

5 files changed, 184 insertions, 8 deletions

diff --git a/README.md b/README.md
index 960bc58..bb78be6 100644
--- a/README.md
+++ b/README.md
@@ -2,24 +2,30 @@
 
 I'm starting over.
 
-## Hexedit
+## Octedit
 
-This is a bare-minimum hex editor
-which fits entirely within the 252-byte boot sector
+This is a bare-minimum memory editor
+which fits entirely within the 256-byte boot sector
 of the Raspberry Pi Pico's on-board flash.
-
 Most of the space is dedicated
 to setting up the clocks, GPIO, and UART.
 
-Enter a series of octal halfwords
+To use, enter a series of octal halfwords over UART
 then press G to jump to the beginning of SRAM
 and begin executing them as instructions.
-
 This is the first step in bootstrapping the whole system.
 
-## Better editor
+## Hexedit
+
+A more robust and user-friendly memory editor,
+which uses hexadecimal instead of octal,
+validates input characters,
+and displays the address and contents
+of the halfword currently being edited.
 
-A more robust and user-friendly hex editor.
+The machine code for this editor
+can be keyed in using octedit
+as a series of 16-bit octal halfwords.
 
 ## Assembler
 
diff --git a/hexedit/Makefile b/hexedit/Makefile
new file mode 100644
index 0000000..4712bd1
--- /dev/null
+++ b/hexedit/Makefile
@@ -0,0 +1,21 @@
+all: build
+
+build: hexedit.uf2
+
+hexedit.uf2: hexedit.elf
+	../elf/elf2uf2 hexedit.elf hexedit.uf2
+
+objects = hexedit.o main.o
+
+hexedit.elf: $(objects)
+	arm-none-eabi-ld -T pico_ram_only.ld -o hexedit.elf $(objects) ../setup/setup.so
+
+$(objects): %.o: %.s
+	arm-none-eabi-as -o $@ $<
+
+clean:
+	rm hexedit.elf hexedit.uf2 *.o
+
+flash: hexedit.uf2
+	[ -h /dev/disk/by-label/RPI-RP2 ] || sleep 2s
+	cat hexedit.uf2 > /dev/disk/by-label/RPI-RP2
diff --git a/hexedit/hexedit.s b/hexedit/hexedit.s
new file mode 100644
index 0000000..fb42d91
--- /dev/null
+++ b/hexedit/hexedit.s
@@ -0,0 +1,122 @@
+.syntax unified
+.cpu cortex-m0plus
+.thumb
+
+.type SETUP, %function
+.global SETUP
+
+.type UARTTX, %function
+.type UARTRX, %function
+.type SENDHEX, %function
+
+.align 4
+
+SETUP:      LDR     R0, [PC, #16] // 000000 044004  UARTRX
+            LDR     R1, [PC, #20] // 000002 044405  UARTTX
+            LDR     R2, [PC, #20] // 000004 045005  SENDHEX
+            MOV     R9, R0        // 000006 043201
+            MOV     R10, R1       // 000010 043212
+            MOV     R11, R2       // 000012 043223
+            LDR     R7, [PC, #4]  // 000014 047401  START ADDRESS
+            ADDS    R6, R7, 1     // 000016 016176
+            B       MAINLOOP      // 000020 160010
+            .HWORD  0x0000        // 000022 000000
+            .WORD   UARTRX        // 000024 010243  0x200010A3
+                                  // 000026 040000
+            .WORD   UARTTX        // 000030 010225  0x20001095
+                                  // 000032 040000
+            .WORD   SENDHEX       // 000034 010264  0x200010B5
+                                  // 000036 040000
+            .WORD   0x20001000    // 000040 010000  START ADDRESS
+                                  // 000042 020000
+MAINLOOP:   MOVS    R0, R7        // 000044 000070  PROMPT
+            BLX     R11           // 000046 043730  SENDHEX
+            MOVS    R0, 0x20      // 000050 020040  SPACE
+            BLX     R10           // 000052 043720  UARTTX
+            LDRH    R0, [R7]      // 000054 104070
+            BLX     R11           // 000056 043730  SENDHEX
+            MOVS    R0, 0x0D      // 000060 020015  CARRIAGE RETURN
+            BLX     R10           // 000062 043720  UARTTX
+            MOVS    R0, R7        // 000064 000070
+            BLX     R11           // 000066 043730  SENDHEX
+            MOVS    R0, 0x20      // 000070 020040  SPACE
+            BLX     R10           // 000072 043720  UARTTX
+10:         BLX     R9            // 000074 043710  COMMAND LOOP, UARTRX
+            CMP     R0, 0x47      // 000076 024107  ASCII G
+            BNE     20f           // 000100 150400
+            BX      R6            // 000102 043460
+20:         CMP     R0, 0x0D      // 000104 024015  CARRIAGE RETURN
+            BNE     30f           // 000106 150401
+            ADDS    R7, 0x2       // 000110 033402
+            B       MAINLOOP      // 000112 163753
+30:         CMP     R0, 0x30      // 000114 024060  ASCII 0
+            BNE     MAINLOOP      // 000116 150751
+            BLX     R10           // 000120 043720  UARTTX
+40:         BLX     R9            // 000122 043710  UARTRX
+            CMP     R0, 0x78      // 000124 024170  ASCII x
+            BNE     40b           // 000126 150774
+            BLX     R10           // 000130 043720  UARTTX
+            MOVS    R4, 0         // 000132 022000
+            MOVS    R5, 4         // 000134 022404
+50:         BLX     R9            // 000136 043710  HEX LOOP, UARTRX
+            CMP     R0, 0x30      // 000140 024060  ASCII 0
+            BLO     50b           // 000142 151774
+            CMP     R0, 0x39      // 000144 024071  ASCII 9
+            BLS     60f           // 000146 154406
+            CMP     R0, 0x41      // 000150 024101  ASCII A
+            BLO     50b           // 000152 151770
+            CMP     R0, 0x46      // 000154 024106  ASCII F
+            BHI     50b           // 000156 154366
+            BLX     R10           // 000160 043720  UARTTX
+            SUBS    R0, 0x37      // 000162 034067  ASCII A MINUS 10
+            B       70f           // 000164 160001
+60:         BLX     R10           // 000166 043720  UARTTX
+            SUBS    R0, 0x30      // 000170 034060  ASCII 0
+70:         LSLS    R4, 4         // 000172 000444
+            ADDS    R4, R0        // 000174 014044
+            SUBS    R5, 1         // 000176 036401
+            BNE     50b           // 000200 150755
+80:         BLX     R9            // 000202 043710  UARTRX
+            CMP     R0, 0x0D      // 000204 024015  CARRIAGE RETURN
+            BNE     80b           // 000206 150774
+            BLX     R10           // 000210 043720  UARTTX
+            STRH    R4, [R7]      // 000212 100074
+            ADDS    R7, 0x2       // 000214 033402
+            MOVS    R0, 0x0A      // 000216 020012  NEW LINE
+            BLX     R10           // 000220 043720  UARTTX
+            B       MAINLOOP      // 000222 163707
+UARTTX:     LDR     R1, [PC, #24] // 000224 044406  UART0_BASE
+            MOVS    R3, 0x20      // 000226 021440  TX FIFO FULL
+1:          LDR     R2, [R1, 0x18]// 000230 067012  UARTFR_OFST
+            TST     R2, R3        // 000232 041032
+            BNE     1b            // 000234 150774
+            STRB    R0, [R1]      // 000236 070010  UARTDR_OFST
+            BX      LR            // 000240 043560
+UARTRX:     LDR     R1, [PC, #12] // 000242 044403
+            MOVS    R3, 0x10      // 000244 021420  RX FIFO EMPTY
+1:          LDR     R2, [R1, 0x18]// 000246 067012  UARTFR_OFST
+            TST     R2, R3        // 000250 041032
+            BNE     1b            // 000252 150774
+            LDRB    R0, [R1]      // 000254 074010  UARTDR_OFST
+            BX      LR            // 000256 043560
+            .WORD   0x40034000    // 000260 040000
+                                  // 000262 040003
+SENDHEX:    PUSH    {LR}          // 000264 132400
+            LSLS    R4, R0, 0x10  // 000266 002004  16 BITS
+            MOVS    R0, 0x30      // 000270 020060  ASCII 0
+            BLX     R10           // 000272 043720  UARTTX
+            MOVS    R0, 0x78      // 000274 020170  ASCII x
+            BLX     R10           // 000276 043720
+            MOVS    R5, 0x4       // 000300 022404
+0:          MOVS    R0, 0x1C      // 000302 020034
+            RORS    R4, R0        // 000304 040704
+            UXTB    R0, R4        // 000306 131340
+            CMP     R0, 0x9       // 000310 024011
+            BHI     1f            // 000312 154001
+            ADDS    R0, 0x30      // 000314 030060  ASCII 0
+            B       2f            // 000316 160000
+1:          ADDS    R0, 0x37      // 000320 030067  ASCII A MINUS 10
+2:          BLX     R10           // 000322 043720  UARTTX
+            SUBS    R5, 1         // 000324 036401
+            BNE     0b            // 000326 150764
+            POP     {PC}          // 000330 136400
diff --git a/hexedit/main.s b/hexedit/main.s
new file mode 100644
index 0000000..0b49339
--- /dev/null
+++ b/hexedit/main.s
@@ -0,0 +1,13 @@
+.syntax unified
+.cpu cortex-m0plus
+.thumb
+
+.type main, %function
+.global main
+
+main:
+  bl start_xosc
+  bl setup_clocks
+  bl setup_gpio
+  bl setup_uart
+  b SETUP
diff --git a/hexedit/pico_ram_only.ld b/hexedit/pico_ram_only.ld
new file mode 100644
index 0000000..1185af5
--- /dev/null
+++ b/hexedit/pico_ram_only.ld
@@ -0,0 +1,14 @@
+ENTRY(main)
+
+MEMORY {
+  FLASH(rx) : ORIGIN = 0x10000000, LENGTH = 2M
+  SRAM(rwx) : ORIGIN = 0x20000000, LENGTH = 264K
+}
+
+SECTIONS {
+  .text : {
+    main.o(.text);
+    *(.text);
+    . = ALIGN(4);
+  } > SRAM
+}