/
mailbox.s
executable file
·68 lines (60 loc) · 1.5 KB
/
mailbox.s
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/******************************************************************************
* mailbox.s
* by Alex Chadwick
*
* A sample assembly code implementation of the input02 operating system.
* See main.s for details.
*
* mailbox.s contains code that interacts with the mailbox for communication
* with various devices.
******************************************************************************/
/*
* GetMailboxBase returns the base address of the mailbox region as a physical
* address in register r0.
* C++ Signature: void* GetMailboxBase()
*/
.globl GetMailboxBase
GetMailboxBase:
ldr r0,=0x2000B880
mov pc,lr
/*
* MailboxRead returns the current value in the mailbox addressed to a channel
* given in the low 4 bits of r0, as the top 28 bits of r0.
* C++ Signature: u32 MailboxRead(u8 channel)
*/
.globl MailboxRead
MailboxRead:
and r3,r0,#0xf
mov r2,lr
bl GetMailboxBase
mov lr,r2
rightmail$:
wait1$:
ldr r2,[r0,#24]
tst r2,#0x40000000
bne wait1$
ldr r1,[r0,#0]
and r2,r1,#0xf
teq r2,r3
bne rightmail$
and r0,r1,#0xfffffff0
mov pc,lr
/*
* MailboxWrite writes the value given in the top 28 bits of r0 to the channel
* given in the low 4 bits of r1.
* C++ Signature: void MailboxWrite(u32 value, u8 channel)
*/
.globl MailboxWrite
MailboxWrite:
and r2,r1,#0xf
and r1,r0,#0xfffffff0
orr r1,r2
mov r2,lr
bl GetMailboxBase
mov lr,r2
wait2$:
ldr r2,[r0,#24]
tst r2,#0x80000000
bne wait2$
str r1,[r0,#32]
mov pc,lr