FPGA asm programs

Author: redfast00

asm/fpga_bootloader.asm

@@ -0,0 +1,95 @@
+.text
+  .global main:
+
+; (blocking) reads one char from uart to the D register
+; pollutes A, B, C, D
+; needs 1 stack space
+uart_read_char:
+  ; push address of misc.in (which contains if uart is writeable/readable), and read option
+  LDV B, (0b110)
+  PSH B
+  SYS
+  ; pop read value in B
+  POP B
+  ; get second-to-last bit: AND with 2
+  LDV A, 2
+  AND A, B
+  ; if A now contains 2, that means we can read from uart
+  LDV C, uart_read_char:
+  LDV B, 2
+  ; if A == 0, then A < B and we will retry
+  JLT B, C
+
+  ; read from uart to D register
+
+  LDV A, (0b1010)
+  PSH A
+  SYS
+  POP D
+  RET
+
+; (blocking) write the D register to uart
+; pollutes A, B, C
+; needs 2 stack space
+uart_send_char:
+    LDV B, (0b110)
+    PSH B
+    SYS
+    ; pop read value in B
+    POP B
+    ; get last bit: AND with 1
+    LDV A, 1
+    AND A, B
+    ; if A now contains 1, that means we can write to uart
+    LDV C, uart_send_char:
+    LDV B, 1
+    ; if A == 0, then A < B and we will retry
+    JLT B, C
+
+    ; else write to uart
+    PSH D
+    LDV A, (0b1001)
+    PSH A
+    SYS
+    RET
+
+; blocking, reads two chars from uart into a 16-bit value into the D register
+; the first character is the most significant byte, the second character the least
+; pollutes A, B, C, D
+read_16_bits_from_uart:
+    LDV A, uart_read_char:
+    CAL A
+    ; D contains the first 8 bits of the address, shift it and push it onto the stack
+    LSH D, 7
+    LSH D, 1
+    PSH D
+    LDV A, uart_read_char:
+    CAL A
+    ; D now contains the last 8 bits of the address
+
+    POP C
+    ; C now contains the first 8 bits of the address
+
+    OR D, C
+    ; now D contains the full address
+    RET
+
+main:
+    ; send a single '>'
+    LDV A, uart_send_char:
+    LDV D, 62
+    CAL A
+
+    LDV A, read_16_bits_from_uart:
+    CAL A
+    ; push the address onto the stack
+    PSH D
+    LDV A, read_16_bits_from_uart:
+    CAL A
+    ; the value to load is now in the D register
+    POP C
+    LDP C, D
+    ; The first ever instruction will be a jump to main
+    ; this makes it easy to transfer control flow to the now-loaded program:
+    ; you just need to overwrite the jump in address 0 with a jump to your loaded program
+    JMP 0

asm/fpga_sys_debug.asm

@@ -0,0 +1,13 @@
+.text
+  .global main:
+
+test:
+    LDV A, 20
+    PSH A
+    POP D
+    RET
+
+main:
+    LDV A, test:
+    CAL A
+    HLT

asm/fpga_uart_recv_send.asm

@@ -0,0 +1,69 @@
+.text
+  .global main:
+
+; (blocking) reads one char from uart to the D register
+; pollutes A, B, C, D
+uart_read_char:
+  ; push address of misc.in (which contains if uart is writeable/readable), and read option
+  LDV B, (0b110)
+  PSH B
+  SYS
+  ; pop read value in B
+  POP B
+  ; get second-to-last bit: AND with 2
+  LDV A, 2
+  AND A, B
+  ; if A now contains 2, that means we can read from uart
+  LDV C, uart_read_char:
+  LDV B, 2
+  ; if A == 0, then A < B and we will retry
+  JLT B, C
+
+  ; read from uart to D register
+
+  LDV A, (0b1010)
+  PSH A
+  SYS
+  POP D
+  RET
+
+; (blocking) write the D register to uart
+; pollutes A, B, C
+uart_send_char:
+    LDV B, (0b110)
+    PSH B
+    SYS
+    ; pop read value in B
+    POP B
+    ; get last bit: AND with 1
+    LDV A, 1
+    AND A, B
+    ; if A now contains 1, that means we can write to uart
+    LDV C, uart_send_char:
+    LDV B, 1
+    ; if A == 0, then A < B and we will retry
+    JLT B, C
+
+    ; else write to uart
+    PSH D
+    LDV A, (0b1001)
+    PSH A
+    SYS
+    RET
+
+main:
+    LDV A, uart_send_char:
+     ; '|'
+    LDV D, 124
+    CAL A
+    LDV A, uart_send_char:
+    ; '>'
+    LDV D, 62
+    CAL A
+    LDV A, uart_read_char:
+    CAL A
+    ; D contains the read character
+    INC D
+    LDV A, uart_send_char:
+    CAL A
+    JMP main: