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Use a register to hold base address of SGPIO interrupt registers.

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This allows us to use ldr/str with an immediate offset to access the
SGPIO interrupt registers, rather than first having to load a register
with the specific address we want to access.

This change saves a total of 6 cycles, by eliminating two loads (2
cycles each), one of which could be executed twice.
This commit is contained in:
Martin Ling
2021-12-20 12:36:22 +00:00
parent 9206a8b752
commit 8f43dc1be5
1 changed files with 12 additions and 10 deletions
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22
firmware/hackrf_usb/sgpio_m0.s
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@ -66,8 +66,8 @@ shadow registers.
There are two key code paths, with the following worst-case timings:
RX: 157 cycles
TX: 142 cycles
RX: 151 cycles
TX: 136 cycles
Design
======
@ -92,10 +92,12 @@ registers and fixed memory addresses.
// Constants that point to registers we'll need to modify in the SGPIO block.
.equ SGPIO_REGISTER_BLOCK_BASE, 0x40101000
.equ SGPIO_SHADOW_REGISTERS_BASE, 0x40101100
.equ SGPIO_EXCHANGE_INTERRUPT_CLEAR_REG, 0x40101F30
.equ SGPIO_EXCHANGE_INTERRUPT_STATUS_REG, 0x40101F2C
.equ SGPIO_EXCHANGE_INTERRUPT_BASE, 0x40101F00
.equ SGPIO_GPIO_INPUT, 0x40101210
// Offsets into the interrupt control registers.
.equ INT_CLEAR, 0x30
.equ INT_STATUS, 0x2C
// Buffer that we're funneling data to/from.
.equ TARGET_DATA_BUFFER, 0x20008000
@ -119,7 +121,8 @@ registers and fixed memory addresses.
/* Allocations of single-use registers */
sgpio_data .req r7
buf_ptr .req r6
sgpio_int .req r6
buf_ptr .req r5
// Entry point. At this point, the libopencm3 startup code has set things up as
// normal; .data and .bss are initialised, the stack is set up, etc. However,
@ -128,7 +131,8 @@ buf_ptr .req r6
.global main
.thumb_func
main: // Cycle counts:
// Grab the base address of the SGPIO shadow registers...
// Initialise registers used for constant values.
ldr sgpio_int, =SGPIO_EXCHANGE_INTERRUPT_BASE // 2
ldr sgpio_data, =SGPIO_SHADOW_REGISTERS_BASE // 2
loop:
// The worst case timing is assumed to occur when reading the interrupt
@ -147,8 +151,7 @@ loop:
// Spin until we're ready to handle an SGPIO packet:
// Grab the exchange interrupt staus...
ldr r0, =SGPIO_EXCHANGE_INTERRUPT_STATUS_REG // 2, twice
ldr r0, [r0] // 10, twice
ldr r0, [sgpio_int, #INT_STATUS] // 10, twice
// ... check to see if it has any interrupt bits set...
lsr r0, #1 // 1, twice
@ -157,9 +160,8 @@ loop:
bcc loop // 3, then 1
// Clear the interrupt pending bits for the SGPIO slices we're working with.
ldr r0, =SGPIO_EXCHANGE_INTERRUPT_CLEAR_REG // 2
ldr r1, =0xffff // 2
str r1, [r0] // 8
str r1, [sgpio_int, #INT_CLEAR] // 8
// ... and grab the address of the buffer segment we want to write to / read from.
ldr r0, =TARGET_DATA_BUFFER // r0 = &buffer // 2