picorv32/picosoc/start.s

.section .text

start:

# zero-initialize register file
addi x1, zero, 0
# x2 (sp) is initialized by reset
addi x3, zero, 0
addi x4, zero, 0
addi x5, zero, 0
addi x6, zero, 0
addi x7, zero, 0
addi x8, zero, 0
addi x9, zero, 0
addi x10, zero, 0
addi x11, zero, 0
addi x12, zero, 0
addi x13, zero, 0
addi x14, zero, 0
addi x15, zero, 0
addi x16, zero, 0
addi x17, zero, 0
addi x18, zero, 0
addi x19, zero, 0
addi x20, zero, 0
addi x21, zero, 0
addi x22, zero, 0
addi x23, zero, 0
addi x24, zero, 0
addi x25, zero, 0
addi x26, zero, 0
addi x27, zero, 0
addi x28, zero, 0
addi x29, zero, 0
addi x30, zero, 0
addi x31, zero, 0

# Update LEDs
li a0, 0x03000000
li a1, 1
sw a1, 0(a0)

# zero initialize entire scratchpad memory
li a0, 0x00000000
setmemloop:
sw a0, 0(a0)
addi a0, a0, 4
blt a0, sp, setmemloop

# Update LEDs
li a0, 0x03000000
li a1, 3
sw a1, 0(a0)

# copy data section
la a0, _sidata
la a1, _sdata
la a2, _edata
bge a1, a2, end_init_data
loop_init_data:
lw a3, 0(a0)
sw a3, 0(a1)
addi a0, a0, 4
addi a1, a1, 4
blt a1, a2, loop_init_data
end_init_data:

# Update LEDs
li a0, 0x03000000
li a1, 7
sw a1, 0(a0)

# zero-init bss section
la a0, _sbss
la a1, _ebss
bge a0, a1, end_init_bss
loop_init_bss:
sw zero, 0(a0)
addi a0, a0, 4
blt a0, a1, loop_init_bss
end_init_bss:

# Update LEDs
li a0, 0x03000000
li a1, 15
sw a1, 0(a0)

# call main
call main
loop:
j loop

.global flashio_worker_begin
.global flashio_worker_end

.balign 4

flashio_worker_begin:
# a0 ... data pointer
# a1 ... data length
# a2 ... optional WREN cmd (0 = disable)

# address of SPI ctrl reg
li   t0, 0x02000000

# Set CS high, IO0 is output
li   t1, 0x120
sh   t1, 0(t0)

# Enable Manual SPI Ctrl
sb   zero, 3(t0)

# Send optional WREN cmd
beqz a2, flashio_worker_L1
li   t5, 8
andi t2, a2, 0xff
flashio_worker_L4:
srli t4, t2, 7
sb   t4, 0(t0)
ori  t4, t4, 0x10
sb   t4, 0(t0)
slli t2, t2, 1
andi t2, t2, 0xff
addi t5, t5, -1
bnez t5, flashio_worker_L4
sb   t1, 0(t0)

# SPI transfer
flashio_worker_L1:
beqz a1, flashio_worker_L3
li   t5, 8
lbu  t2, 0(a0)
flashio_worker_L2:
srli t4, t2, 7
sb   t4, 0(t0)
ori  t4, t4, 0x10
sb   t4, 0(t0)
lbu  t4, 0(t0)
andi t4, t4, 2
srli t4, t4, 1
slli t2, t2, 1
or   t2, t2, t4
andi t2, t2, 0xff
addi t5, t5, -1
bnez t5, flashio_worker_L2
sb   t2, 0(a0)
addi a0, a0, 1
addi a1, a1, -1
j    flashio_worker_L1
flashio_worker_L3:

# Back to MEMIO mode
li   t1, 0x80
sb   t1, 3(t0)

ret

.balign 4
flashio_worker_end: