(machine.SPI).txrx

dissassemble machine.SPI.txrx

(gdb) disassemble 
Dump of assembler code for function (machine.SPI).txrx:
   0x00005b82 <+0>:     stmdb   sp!, {r4, r5, r6, r7, r8, r9, r10, r11, lr}
   0x00005b86 <+4>:     sub     sp, #12
=> 0x00005b88 <+6>:     cmp     r0, #0
   0x00005b8a <+8>:     str     r3, [sp, #8]
   0x00005b8c <+10>:    beq.n   0x5c24 <(machine.SPI).txrx+162>
   0x00005b8e <+12>:    mov     r11, r2
   0x00005b90 <+14>:    cmp     r2, #0
   0x00005b92 <+16>:    beq.n   0x5c20 <(machine.SPI).txrx+158>
   0x00005b94 <+18>:    mov     r9, r1
   0x00005b96 <+20>:    add.w   r5, r0, #40     ; 0x28
   0x00005b9a <+24>:    ldrb    r1, [r1, #0]
   0x00005b9c <+26>:    str     r0, [sp, #4]
   0x00005b9e <+28>:    mov     r0, r5
   0x00005ba0 <+30>:    ldr     r7, [sp, #48]   ; 0x30
   0x00005ba2 <+32>:    bl      0xecfe <(*runtime/volatile.Register32).Set>
   0x00005ba6 <+36>:    cmp     r7, #2
   0x00005ba8 <+38>:    blt.n   0x5bf8 <(machine.SPI).txrx+118>
   0x00005baa <+40>:    ldr     r0, [sp, #4]
   0x00005bac <+42>:    adds    r6, r7, #1
   0x00005bae <+44>:    mov.w   r8, #1
   0x00005bb2 <+48>:    add.w   r4, r0, #24
   0x00005bb6 <+52>:    mov     r0, r4
   0x00005bb8 <+54>:    movs    r1, #1
   0x00005bba <+56>:    bl      0xede8 <(*runtime/volatile.Register8).HasBits>
   0x00005bbe <+60>:    lsls    r0, r0, #31
   0x00005bc0 <+62>:    beq.n   0x5bb6 <(machine.SPI).txrx+52>
   0x00005bc2 <+64>:    cmp     r8, r11
   0x00005bc4 <+66>:    beq.n   0x5c20 <(machine.SPI).txrx+158>
   0x00005bc6 <+68>:    ldrb.w  r1, [r9, r8]
   0x00005bca <+72>:    mov     r0, r5
   0x00005bcc <+74>:    bl      0xecfe <(*runtime/volatile.Register32).Set>
   0x00005bd0 <+78>:    mov     r0, r4
   0x00005bd2 <+80>:    movs    r1, #4
   0x00005bd4 <+82>:    bl      0xede8 <(*runtime/volatile.Register8).HasBits>
   0x00005bd8 <+86>:    lsls    r0, r0, #31
   0x00005bda <+88>:    beq.n   0x5bd0 <(machine.SPI).txrx+78>
   0x00005bdc <+90>:    cmp     r8, r6
   0x00005bde <+92>:    beq.n   0x5c20 <(machine.SPI).txrx+158>
   0x00005be0 <+94>:    ldr     r0, [sp, #8]
   0x00005be2 <+96>:    add.w   r10, r8, r0
   0x00005be6 <+100>:   mov     r0, r5
   0x00005be8 <+102>:   bl      0xecb4 <(*runtime/volatile.Register32).Get>
   0x00005bec <+106>:   add.w   r8, r8, #1
   0x00005bf0 <+110>:   strb.w  r0, [r10, #-1]
   0x00005bf4 <+114>:   cmp     r8, r7
   0x00005bf6 <+116>:   bne.n   0x5bb6 <(machine.SPI).txrx+52>
   0x00005bf8 <+118>:   ldr     r0, [sp, #4]
   0x00005bfa <+120>:   add.w   r4, r0, #24
   0x00005bfe <+124>:   mov     r0, r4
   0x00005c00 <+126>:   movs    r1, #4
   0x00005c02 <+128>:   bl      0xede8 <(*runtime/volatile.Register8).HasBits>
   0x00005c06 <+132>:   lsls    r0, r0, #31
   0x00005c08 <+134>:   beq.n   0x5bfe <(machine.SPI).txrx+124>
   0x00005c0a <+136>:   cbz     r7, 0x5c20 <(machine.SPI).txrx+158>
   0x00005c0c <+138>:   ldr     r0, [sp, #8]
   0x00005c0e <+140>:   adds    r4, r7, r0
   0x00005c10 <+142>:   mov     r0, r5
   0x00005c12 <+144>:   bl      0xecb4 <(*runtime/volatile.Register32).Get>
   0x00005c16 <+148>:   strb.w  r0, [r4, #-1]
   0x00005c1a <+152>:   add     sp, #12
   0x00005c1c <+154>:   ldmia.w sp!, {r4, r5, r6, r7, r8, r9, r10, r11, pc}
   0x00005c20 <+158>:   bl      0x7696 <runtime.lookupPanic>
   0x00005c24 <+162>:   bl      0x7768 <runtime.nilPanic>
End of assembler dump.

txrx

func (spi SPI) txrx(tx, rx []byte) {
	spi.Bus.DATA.Set(uint32(tx[0]))

	for i := 1; i < len(rx); i++ {
		for !spi.Bus.INTFLAG.HasBits(sam.SERCOM_SPIM_INTFLAG_DRE) {
		}
		spi.Bus.DATA.Set(uint32(tx[i]))
		for !spi.Bus.INTFLAG.HasBits(sam.SERCOM_SPIM_INTFLAG_RXC) {
		}
		rx[i-1] = byte(spi.Bus.DATA.Get())
	}
	for !spi.Bus.INTFLAG.HasBits(sam.SERCOM_SPIM_INTFLAG_RXC) {
	}
	rx[len(rx)-1] = byte(spi.Bus.DATA.Get())
}

volatile.Register8.Get

(gdb) disassemble
Dump of assembler code for function (*runtime/volatile.Register8).Get:
   0x0000ed1e <+0>:     push    {r7, lr}
=> 0x0000ed20 <+2>:     cmp     r0, #0
   0x0000ed22 <+4>:     itt     ne
   0x0000ed24 <+6>:     ldrbne  r0, [r0, #0]
   0x0000ed26 <+8>:     popne   {r7, pc}
   0x0000ed28 <+10>:    bl      0x7768 <runtime.nilPanic>
End of assembler dump.


// Get returns the value in the register. It is the volatile equivalent of:
//
//     *r.Reg
//
//go:inline
func (r *Register8) Get() uint8 {
	return LoadUint8(&r.Reg)
}

volatile.Register8.HasBits

(gdb) disassemble
Dump of assembler code for function (*runtime/volatile.Register8).HasBits:
   0x0000ede8 <+0>:     push    {r4, lr}
   0x0000edea <+2>:     mov     r4, r1
=> 0x0000edec <+4>:     bl      0xed1e <(*runtime/volatile.Register8).Get>
   0x0000edf0 <+8>:     ands    r0, r4
   0x0000edf2 <+10>:    uxtb    r0, r0
   0x0000edf4 <+12>:    cmp     r0, #0
   0x0000edf6 <+14>:    it      ne
   0x0000edf8 <+16>:    movne   r0, #1
   0x0000edfa <+18>:    pop     {r4, pc}
End of assembler dump.

// HasBits reads the register and then checks to see if the passed bits are set. It
// is the volatile equivalent of:
//
//     (*r.Reg & value) > 0
//
//go:inline
func (r *Register8) HasBits(value uint8) bool {
	return (r.Get() & value) > 0
}