@Bill's Notes 21st October 2026 app.a
.syntax unified; .cpu cortex-m33; .thumb
.include "C:/5e5/STM32H5E5.inc"
.section .text; .word RAM1_POST; .word init + 1
.global init; init:

@prime tx fifo before clocking
ldr r0,=SPI1_BASE; ldr r1,=0x5a5a5a5a
str r1,[r0,#SPI1_TXDR]; str r1,[r0,#SPI1_TXDR]; str r1,[r0,#SPI1_TXDR]; str r1,[r0,#SPI1_TXDR] 
 
@wait for SPI rx fifo full (RXP)
next_trans: ldr r0,=SPI1_BASE; wait1: ldr r2,[r0,#SPI1_SR]; tst r2,#(1<<0); beq wait1
ldr r4,[r0,#SPI1_RXDR]; ldr r5,[r0,#SPI1_RXDR]; ldr r6,[r0,#SPI1_RXDR]; ldr r7,[r0,#SPI1_RXDR] @read spi1 rx
str r7,[r0,#SPI1_TXDR]; str r5,[r0,#SPI1_TXDR]; str r6,[r0,#SPI1_TXDR]; str r4,[r0,#SPI1_TXDR] @reverse spi1 tx

@dispatch transaction using token method
ldr r0,=token_base; ldr r1,=token_end
token_loop: ldmia r0!,{r2,r3}; cmp r2,r4; beq match; cmp r0,r1; blo token_loop; b next_trans; match: bx r3

@wait for SPI tx empty (TXP) and rx fifo full (RXP)
ram_load: ldr r0,=SPI1_BASE; wait2: ldr r2,[r0,#SPI1_SR]; tst r2,#(1<<1); beq wait2 @test TXP
str r4,[r0,#SPI1_TXDR]; str r5,[r0,#SPI1_TXDR]; str r6,[r0,#SPI1_TXDR]; str r7,[r0,#SPI1_TXDR] @prime tx fifo
wait3: ldr r2,[r0,#SPI1_SR]; tst r2,#(1<<0); beq wait3 @test RXP
@store four words in ram (r5 holds ram base address r6 holds the ram end address)
ldr r2,[r0,#SPI1_RXDR]; str r2,[r5]; add r5,r5,#0x04; ldr r2,[r0,#SPI1_RXDR]; str r2,[r5]; add r5,r5,#0x04
ldr r2,[r0,#SPI1_RXDR]; str r2,[r5]; add r5,r5,#0x04; ldr r2,[r0,#SPI1_RXDR]; str r2,[r5]; add r5,r5,#0x04
ldr r7,[r0,#SPI1_SR]; cmp r5,r6; blo ram_load; b next_trans @put SPI1_SR into r7 for spi1 tx (status info)

@branch to the app loaded to ram
ram_run: ldr sp,[r5]; ldr r1,[r5, #0x04]; bx r1

spi1_test:  b next_trans

.align 4;

token_base:
.word 0x91578dd4,spi1_test+1
.word 0x3d28e804,ram_load+1
.word 0x607f096d,ram_run+1
.word 0xa54c9b21,next_trans+1
.word 0xd1e45abd,next_trans+1
.word 0x3df3dce0,next_trans+1
.word 0x9caf78bd,next_trans+1
.word 0x47e3a33b,next_trans+1
.word 0x7a5318c2,next_trans+1
.word 0x7f820d3b,next_trans+1
token_end:

.ltorg; .org 0x10000