Finish hexedit and update README

7 files changed, 67 insertions, 70 deletions

diff --git a/README.md b/README.md
index 032ff5b..8ebd951 100644
--- a/README.md
+++ b/README.md
@@ -11,14 +11,37 @@ of the Raspberry Pi Pico's on-board flash.
 Most of the space is dedicated
 to setting up the clocks, GPIO, and UART.
 
-Current status: almost complete.
-Right now it simply echos characters received over UART.
+Enter a series of octal halfwords
+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
+
+%% A more robust and user-friendly hex-editor.
+%% It can duplicate itself.
 
 ## Assembler
 
-An assembler that can assemble itself (WIP)
+This is a single-pass assembler
+supporting most of the ARMv6-M instruction set
+using a simplified instruction syntax
+in which there are
+no labels,
+only octal literals,
+and unambiguous instruction mnemonics.
+
+It does not allow the user to type invalid instructions.
+
+## Better Assembler
 
 Goals:
 - A subset of GNU `as` syntax
 - Reasonably extensible
 - Small code size
+
+%% ## LISP Interpreter
+
+%% A LISP interpreter for the Raspberry Pi Pico,
+%% developed ON a raspberry pi pico
diff --git a/assembler/assemble.s b/assembler/assemble.s
index 7dec597..6ef1436 100644
--- a/assembler/assemble.s
+++ b/assembler/assemble.s
@@ -8,7 +8,6 @@
 // TODO:
 // - test each instruction
 // - decide on additional push or pops
-// - add data literal "instructions"
 // - redo_line is problematic
 // - PP and PL are broken (end char)
 
diff --git a/hexedit/Makefile b/hexedit/Makefile
index 2ff0812..d862c25 100644
--- a/hexedit/Makefile
+++ b/hexedit/Makefile
@@ -1,21 +1,21 @@
 all: build
 
-build: echo.uf2
+build: hexedit.uf2
 
-echo.uf2: echo.elf
-	../elf/elf2uf2 echo.elf echo.uf2
+hexedit.uf2: hexedit.elf
+	../elf/elf2uf2 hexedit.elf hexedit.uf2
 
-objects = main.o uart.o
+objects = main.o uart.o hexedit.o
 
-echo.elf: $(objects)
-	arm-none-eabi-ld -T pico_ram_only.ld -o echo.elf $(objects) ../setup/setup.so
+hexedit.elf: $(objects)
+	arm-none-eabi-ld -T pico_persist.ld -o hexedit.elf $(objects) ../setup/setup.so
 
 $(objects): %.o: %.s
 	arm-none-eabi-as -o $@ $<
 
 clean:
-	rm echo.elf echo.uf2 *.o
+	rm hexedit.elf hexedit.uf2 *.o
 
-flash: echo.uf2
+flash: hexedit.uf2
 	[ -h /dev/disk/by-label/RPI-RP2 ] || sleep 3s
-	cat echo.uf2 > /dev/disk/by-label/RPI-RP2
+	cat hexedit.uf2 > /dev/disk/by-label/RPI-RP2
diff --git a/hexedit/hexedit.s b/hexedit/hexedit.s
index 0bc03a9..26bc84b 100644
--- a/hexedit/hexedit.s
+++ b/hexedit/hexedit.s
@@ -2,24 +2,34 @@
 .cpu cortex-m0plus
 .thumb
 
+.equ SRAM_BASE, 0x20000000
+
 .type hexedit, %function
 .global hexedit
 
 hexedit:
-  ldr r2, =0x20000100
-  movs r1, 0
-getchar:
+  ldr r6, =SRAM_BASE
+  adds r5, r6, 1
+10:
+  movs r4, 0
+20:
   bl uart_recv
-  cmp r0, 'g
-  beq stop
-  subs r0, '0 // The ASCII char '0'
-  bmi next
-  lsls r1, 4
-  adds r1, r0
-  b getchar
-next:
-  ldr r0, [r2, 0]
-  adds r2, 4
-  b hexedit
-stop:
-  b 0x20000100
+  cmp r0, '\r
+  beq 30f
+  cmp r0, 'G
+  beq 40f
+  bl uart_send
+  subs r0, '0
+  lsls r4, 3
+  adds r4, r0
+  b 20b
+30:
+  movs r0, '\r
+  bl uart_send
+  movs r0, '\n
+  bl uart_send
+  strh r4, [r6]
+  adds r6, 2
+  b 10b
+40:
+  bx r5
diff --git a/hexedit/main.s b/hexedit/main.s
index 5e294d4..f2f6126 100644
--- a/hexedit/main.s
+++ b/hexedit/main.s
@@ -2,6 +2,8 @@
 .cpu cortex-m0plus
 .thumb
 
+.section .entry, "ax"
+
 .type main, %function
 .global main
 
@@ -10,7 +12,4 @@ main:
   bl setup_clocks
   bl setup_gpio
   bl setup_uart
-1:
-  bl uart_recv
-  bl uart_send
-  b 1b
+  b hexedit
diff --git a/hexedit/pico_ram_only.ld b/hexedit/pico_persist.ld
index eb2450e..32cc42f 100644
--- a/hexedit/pico_ram_only.ld
+++ b/hexedit/pico_persist.ld
@@ -1,13 +1,11 @@
-ENTRY(main)
-
 MEMORY {
   FLASH(rx) : ORIGIN = 0x10000000, LENGTH = 2M
-  SRAM(rwx) : ORIGIN = 0x20000000, LENGTH = 264K
+  SRAM(rx) : ORIGIN = 0x20041f00, LENGTH = 252
 }
 
 SECTIONS {
   .text : {
+    *(.entry)
     *(.text)
-    . = ALIGN(4);
-  } > SRAM
+  } >SRAM AT>FLASH
 }
diff --git a/hexedit/uart.s b/hexedit/uart.s
index b845c8b..e79cbdc 100644
--- a/hexedit/uart.s
+++ b/hexedit/uart.s
@@ -31,35 +31,3 @@ uart_recv:
   bne 1b
   ldrb r0, [r1, UARTDR_OFST]
   bx lr
-
-.type send_hex, %function
-.global send_hex
-
-send_hex:
-  push {lr}
-  movs r4, r0
-  movs r0, '0
-  bl uart_send
-  movs r0, 'x
-  bl uart_send
-  movs r5, 8 // eight nibbles in a word
-0:
-  movs r0, 28 // rotate left 4
-  rors r4, r0
-  movs r0, 0xF // lowest nibble mask
-  ands r0, r4
-  cmp r0, 0x9 // number or letter?
-  bhi 1f
-  adds r0, '0
-  b 2f
-1:
-  adds r0, ('A - 0xA)
-2:
-  bl uart_send
-  subs r5, 1
-  bne 0b
-  movs r0, '\r
-  bl uart_send
-  movs r0, '\n
-  bl uart_send
-  pop {pc}